Zhenan Bao

All Publications

• Additively manufactured micro-lattice dielectrics for multiaxial capacitive sensors. Science advances Berman, A., Hsiao, K., Root, S. E., Choi, H., Ilyn, D., Xu, C., Stein, E., Cutkosky, M., DeSimone, J. M., Bao, Z. 2024; 10 (40): eadq8866

  Abstract

  Soft sensors that can perceive multiaxial forces, such as normal and shear, are of interest for dexterous robotic manipulation and monitoring of human performance. Typical planar fabrication techniques have substantial design constraints that often prohibit the creation of functionally compelling and complex architectures. Moreover, they often require multiple-step operations for production. Here, we use an additive manufacturing process based on continuous liquid interface production to create high-resolution (30-micrometer) three-dimensional elastomeric polyurethane lattices for use as dielectric layers in capacitive sensors. We show that the capacitive responses and sensitivities are highly tunable through designs of lattice type, thickness, and material-void volume percentage. Microcomputed tomography and finite element simulation are used to elucidate the influence of lattice design on the deformation mechanism and concomitant sensing behavior. The advantage of three-dimensional printing is exhibited with examples of fully printed representative athletic equipment with integrated sensors.

  View details for DOI 10.1126/sciadv.adq8866

  View details for PubMedID 39365852

• A Transparent, Patternable, and Stretchable Conducting Polymer Solid Electrode for Dielectric Elastomer Actuators ADVANCED FUNCTIONAL MATERIALS Kim, E., Lai, J., Michalek, L., Wang, W., Xu, C., Lyu, H., Yu, W., Park, H., Tomo, Y., Root, S. E., Lee, B., Park, J., Park, B., Wei, S., Zhao, C., Bao, Z. 2024

  View details for DOI 10.1002/adfm.202411880

  View details for Web of Science ID 001300258000001

• Mesomeric control of the optoelectronic properties of polymerized small molecule acceptors JOURNAL OF MATERIALS CHEMISTRY A Sorbelli, D., Wu, Y., Bao, Z., Galli, G. 2024

  View details for DOI 10.1039/d4ta04192e

  View details for Web of Science ID 001297936600001

• Failure Process During Fast Charging of Lithium Metal Batteries with Weakly Solvating Fluoroether Electrolytes JOURNAL OF PHYSICAL CHEMISTRY C Chen, Y., Yu, Z., Gong, H., Zhang, W., Rudnicki, P. E., Huang, Z., Yu, W., Kim, S., Boyle, D. T., Sayavong, P., Celik, H., Xu, R., Lin, Y., Wang, S., Qin, J., Cui, Y., Bao, Z. 2024

  View details for DOI 10.1021/acs.jpcc.4c01740

  View details for Web of Science ID 001265561200001

• Applications of synthetic polymers directed toward living cells NATURE SYNTHESIS Zhang, A., Zhao, S., Tyson, J., Deisseroth, K., Bao, Z. 2024

  View details for DOI 10.1038/s44160-024-00560-2

  View details for Web of Science ID 001251905000003

• Network Evolution Controlling Strain-Induced Damage and Self-Healing of Elastomers with Dynamic Bonds MACROMOLECULES Yin, Y., Mohanty, S., Cooper, C. B., Bao, Z., Cai, W. 2024

  View details for DOI 10.1021/acs.macromol.4c00409

  View details for Web of Science ID 001250624800001

• Shape-memory-assisted self-healing of macroscopic punctures via high-energy-density periodic dynamic polymers with tunable actuation temperature MATTER Shi, Y., Cooper, C. B., Nogusa, T., Lai, J., Lyu, H., Khatib, M., Xu, C., Michalek, L., Bao, Z. 2024; 7 (6)

  View details for DOI 10.1016/j.matt.2024.03.013

  View details for Web of Science ID 001259507400001

• Tuning Two-Dimensional Phthalocyanine Dual Site Metal-Organic Framework Catalysts for the Oxygen Reduction Reaction. Journal of the American Chemical Society Wei, L., Hossain, M. D., Chen, G., Kamat, G. A., Kreider, M. E., Chen, J., Yan, K., Bao, Z., Bajdich, M., Stevens, M. B., Jaramillo, T. F. 2024

  Abstract

  Metal-organic frameworks (MOFs) offer an interesting opportunity for catalysis, particularly for metal-nitrogen-carbon (M-N-C) motifs by providing an organized porous structural pattern and well-defined active sites for the oxygen reduction reaction (ORR), a key need for hydrogen fuel cells and related sustainable energy technologies. In this work, we leverage electrochemical testing with computational models to study the electronic and structural properties in the MOF systems and their relationship to ORR activity and stability based on dual transitional metal centers. The MOFs consist of two M1 metals with amine nodes coordinated to a single M2 metal with a phthalocyanine linker, where M1/M2 = Co, Ni, or Cu. Co-based metal centers, in particular Ni-Co, demonstrate the highest overall activity of all nine tested MOFs. Computationally, we identify the dominance of Co sites, relative higher importance of the M2 site, and the role of layer M1 interactions on the ORR activity. Selectivity measurements indicate that M1 sites of MOFs, particularly Co, exhibit the lowest (<4%), and Ni demonstrates the highest (>46%) two-electron selectivity, in good agreement with computational studies. Direct in situ stability characterization, measuring dissolved metal ions, and calculations, using an alkaline stability metric, confirm that Co is the most stable metal in the MOF, while Cu exhibits notable instability at the M1. Overall, this study reveals how atomistic coupling of electronic and structural properties affects the ORR performance of dual site MOF catalysts and opens new avenues for the tunable design and future development of these systems for practical electrochemical applications.

  View details for DOI 10.1021/jacs.4c02229

  View details for PubMedID 38709577

• Autonomous self-healing supramolecular polymer transistors for skin electronics. Nature communications Vo, N. T., Nam, T. U., Jeong, M. W., Kim, J. S., Jung, K. H., Lee, Y., Ma, G., Gu, X., Tok, J. B., Lee, T. I., Bao, Z., Oh, J. Y. 2024; 15 (1): 3433

  Abstract

  Skin-like field-effect transistors are key elements of bio-integrated devices for future user-interactive electronic-skin applications. Despite recent rapid developments in skin-like stretchable transistors, imparting self-healing ability while maintaining necessary electrical performance to these transistors remains a challenge. Herein, we describe a stretchable polymer transistor capable of autonomous self-healing. The active material consists of a blend of an electrically insulating supramolecular polymer with either semiconducting polymers or vapor-deposited metal nanoclusters. A key feature is to employ the same supramolecular self-healing polymer matrix for all active layers, i.e., conductor/semiconductor/dielectric layers, in the skin-like transistor. This provides adhesion and intimate contact between layers, which facilitates effective charge injection and transport under strain after self-healing. Finally, we fabricate skin-like self-healing circuits, including NAND and NOR gates and inverters, both of which are critical components of arithmetic logic units. This work greatly advances practical self-healing skin electronics.

  View details for DOI 10.1038/s41467-024-47718-2

  View details for PubMedID 38653966

  View details for PubMedCentralID PMC11039670

• Evolution and Interplay of Lithium Metal Interphase Components Revealed by Experimental and Theoretical Studies. Journal of the American Chemical Society Tan, S., Kuai, D., Yu, Z., Perez-Beltran, S., Rahman, M. M., Xia, K., Wang, N., Chen, Y., Yang, X., Xiao, J., Liu, J., Cui, Y., Bao, Z., Balbuena, P. B., Hu, E. 2024

  Abstract

  Lithium metal batteries (LMB) have high energy densities and are crucial for clean energy solutions. The characterization of the lithium metal interphase is fundamentally and practically important but technically challenging. Taking advantage of synchrotron X-ray, which has the unique capability of analyzing crystalline/amorphous phases quantitatively with statistical significance, we study the composition and dynamics of the LMB interphase for a newly developed important LMB electrolyte that is based on fluorinated ether. Pair distribution function analysis revealed the sequential roles of the anion and solvent in interphase formation during cycling. The relative ratio between Li2O and LiF first increases and then decreases during cycling, suggesting suppressed Li2O formation in both initial and long extended cycles. Theoretical studies revealed that in initial cycles, this is due to the energy barriers in many-electron transfer. In long extended cycles, the anion decomposition product Li2O encourages solvent decomposition by facilitating solvent adsorption on Li2O which is followed by concurrent depletion of both. This work highlights the important role of Li2O in transitioning from an anion-derived interphase to a solvent-derived one.

  View details for DOI 10.1021/jacs.3c14232

  View details for PubMedID 38632847

• Strain-Induced Performance Variation in Stretchable Carbon-Nanotube Thin-Film Transistors and the Solution Through a Circular Channel Design IEEE TRANSACTIONS ON ELECTRON DEVICES Wu, C., Zhong, D., Wang, W., Jiang, Y., Nishio, Y., Yuan, Y., Liu, Q., Tok, J., Bao, Z. 2024

  View details for DOI 10.1109/TED.2024.3377188

  View details for Web of Science ID 001197909900001

• Tuning polymer-backbone coplanarity and conformational order to achieve high-performance printed all-polymer solar cells. Nature communications Wu, Y., Yuan, Y., Sorbelli, D., Cheng, C., Michalek, L., Cheng, H. W., Jindal, V., Zhang, S., LeCroy, G., Gomez, E. D., Milner, S. T., Salleo, A., Galli, G., Asbury, J. B., Toney, M. F., Bao, Z. 2024; 15 (1): 2170

  Abstract

  All-polymer solar cells (all-PSCs) offer improved morphological and mechanical stability compared with those containing small-molecule-acceptors (SMAs). They can be processed with a broader range of conditions, making them desirable for printing techniques. In this study, we report a high-performance polymer acceptor design based on bithiazole linker (PY-BTz) that are on par with SMAs. We demonstrate that bithiazole induces a more coplanar and ordered conformation compared to bithiophene due to the synergistic effect of non-covalent backbone planarization and reduced steric encumbrances. As a result, PY-BTz shows a significantly higher efficiency of 16.4% in comparison to the polymer acceptors based on commonly used thiophene-based linkers (i.e., PY-2T, 9.8%). Detailed analyses reveal that this improvement is associated with enhanced conjugation along the backbone and closer interchain π-stacking, resulting in higher charge mobilities, suppressed charge recombination, and reduced energetic disorder. Remarkably, an efficiency of 14.7% is realized for all-PSCs that are solution-sheared in ambient conditions, which is among the highest for devices prepared under conditions relevant to scalable printing techniques. This work uncovers a strategy for promoting backbone conjugation and planarization in emerging polymer acceptors that can lead to superior all-PSCs.

  View details for DOI 10.1038/s41467-024-46493-4

  View details for PubMedID 38461153

  View details for PubMedCentralID 8440764

• High-speed and large-scale intrinsically stretchable integrated circuits. Nature Zhong, D., Wu, C., Jiang, Y., Yuan, Y., Kim, M., Nishio, Y., Shih, C., Wang, W., Lai, J., Ji, X., Gao, T. Z., Wang, Y., Xu, C., Zheng, Y., Yu, Z., Gong, H., Matsuhisa, N., Zhao, C., Lei, Y., Liu, D., Zhang, S., Ochiai, Y., Liu, S., Wei, S., Tok, J. B., Bao, Z. 2024; 627 (8003): 313-320

  Abstract

  Intrinsically stretchable electronics with skin-like mechanical properties have been identified as a promising platform for emerging applications ranging from continuous physiological monitoring to real-time analysis of health conditions, to closed-loop delivery of autonomous medical treatment1-7. However, current technologies could only reach electrical performance at amorphous-silicon level (that is, charge-carrier mobility of about 1cm2V-1s-1), low integration scale (for example, 54 transistors per circuit) and limited functionalities8-11. Here we report high-density, intrinsically stretchable transistors and integrated circuits with high driving ability, high operation speed and large-scale integration. They were enabled by a combination of innovations in materials, fabrication process design, device engineering and circuit design. Our intrinsically stretchable transistors exhibit an average field-effect mobility of more than 20cm2V-1s-1 under 100% strain, a device density of 100,000 transistors per cm2, including interconnects and a high drive current of around 2muAmum-1 at a supply voltage of 5V. Notably, these achieved parameters are on par with state-of-the-art flexible transistors based on metal-oxide, carbon nanotube and polycrystalline silicon materials on plastic substrates12-14. Furthermore, we realize a large-scale integrated circuit with more than 1,000 transistors and a stage-switching frequency greater than 1MHz, for the first time, to our knowledge, in intrinsically stretchable electronics. Moreover, we demonstrate a high-throughput braille recognition system that surpasses human skin sensing ability, enabled by an active-matrix tactile sensor array with a record-high density of 2,500 units per cm2, and a light-emitting diode display with a high refreshing speed of 60Hz and excellent mechanical robustness. The above advancements in device performance have substantially enhanced the abilities of skin-like electronics.

  View details for DOI 10.1038/s41586-024-07096-7

  View details for PubMedID 38480964

• Solvation-property relationship of lithium-sulphur battery electrolytes. Nature communications Kim, S. C., Gao, X., Liao, S., Su, H., Chen, Y., Zhang, W., Greenburg, L. C., Pan, J., Zheng, X., Ye, Y., Kim, M. S., Sayavong, P., Brest, A., Qin, J., Bao, Z., Cui, Y. 2024; 15 (1): 1268

  Abstract

  The Li-S battery is a promising next-generation battery chemistry that offers high energy density and low cost. The Li-S battery has a unique chemistry with intermediate sulphur species readily solvated in electrolytes, and understanding their implications is important from both practical and fundamental perspectives. In this study, we utilise the solvation free energy of electrolytes as a metric to formulate solvation-property relationships in various electrolytes and investigate their impact on the solvated lithium polysulphides. We find that solvation free energy influences Li-S battery voltage profile, lithium polysulphide solubility, Li-S battery cyclability and the Li metal anode; weaker solvation leads to lower 1st plateau voltage, higher 2nd plateau voltage, lower lithium polysulphide solubility, and superior cyclability of Li-S full cells and Li metal anodes. We believe that relationships delineated in this study can guide the design of high-performance electrolytes for Li-S batteries.

  View details for DOI 10.1038/s41467-023-44527-x

  View details for PubMedID 38341443

• On Stress: Combining Human Factors and Biosignals to Inform the Placement and Design of a Skin-like Stress Sensor Khan, Y., Mauriello, M., Nowruzi, P., Motani, A., Hon, G., Vitale, N., Li, J., Kim, J., Foudeh, A., Duvio, D., Shols, E., Chesnut, M., Landay, J., Liphardt, J., Williams, L., Sudheimer, K. D., Murmann, B., Bao, Z., Paredes, P. E., ACM ASSOC COMPUTING MACHINERY. 2024

  View details for DOI 10.1145/3613904.3643473

  View details for Web of Science ID 001266059704048

• Tuning the Mobility of Indacenodithiophene-Based Conjugated Polymers via Coplanar Backbone Engineering CHEMISTRY OF MATERIALS Ji, X., Cheng, H., Schuster, N. J., LeCroy, G. S., Zhang, S., Wu, Y., Michalek, L., Nguyen, B. T., Chiong, J. A., Schrock, M., Tomo, Y., Rech, J., Salleo, A., Gam, S., Lee, G., Tok, J., Bao, Z. 2023; 36 (1): 256-265

  View details for DOI 10.1021/acs.chemmater.3c02006

  View details for Web of Science ID 001139519300001

• Highly stretchable polymer semiconductor thin films with multi-modal energy dissipation and high relative stretchability. Nature communications Wu, H. C., Nikzad, S., Zhu, C., Yan, H., Li, Y., Niu, W., Matthews, J. R., Xu, J., Matsuhisa, N., Arunachala, P. K., Rastak, R., Linder, C., Zheng, Y. Q., Toney, M. F., He, M., Bao, Z. 2023; 14 (1): 8382

  Abstract

  Stretchable polymer semiconductors (PSCs) have seen great advancements alongside the development of soft electronics. But it remains a challenge to simultaneously achieve high charge carrier mobility and stretchability. Herein, we report the finding that stretchable PSC thin films (<100-nm-thick) with high stretchability tend to exhibit multi-modal energy dissipation mechanisms and have a large relative stretchability (rS) defined by the ratio of the entropic energy dissipation to the enthalpic energy dissipation under strain. They effectively recovered the original molecular ordering, as well as electrical performance, after strain was released. The highest rS value with a model polymer (P4) exhibited an average charge carrier mobility of 0.2 cm2V-1s-1 under 100% biaxial strain, while PSCs with low rS values showed irreversible morphology changes and rapid degradation of electrical performance under strain. These results suggest rS can be used as a parameter to compare the reliability and reversibility of stretchable PSC thin films.

  View details for DOI 10.1038/s41467-023-44099-w

  View details for PubMedID 38104194

  View details for PubMedCentralID 8367968

• Sequence-dependent self-assembly of supramolecular nanofibers in periodic dynamic block copolymers JOURNAL OF MATERIALS CHEMISTRY A Phong, J. K., Cooper, C. B., Michalek, L., Lin, Y., Nishio, Y., Shi, Y., Gong, H., Vigil, J. A., Ilavsky, J., Kuzmenko, I., Bao, Z. 2023

  View details for DOI 10.1039/d3ta06695a

  View details for Web of Science ID 001125326700001

• Thank You, Elsa! A Virtual Special Issue in Honor of Professor Elsa Reichmanis CHEMISTRY OF MATERIALS Bao, Z., Diao, Y., Wang, G., Risko, C. 2023; 35 (23): 9819-9820

  View details for DOI 10.1021/acs.chemmater.3c02527

  View details for Web of Science ID 001141585700001

• Impact of the fluorination degree of ether-based electrolyte solvents on Li-metal battery performance JOURNAL OF MATERIALS CHEMISTRY A Lin, Y., Yu, Z., Yu, W., Liao, S., Zhang, E., Guo, X., Huang, Z., Chen, Y., Qin, J., Cui, Y., Bao, Z. 2023

  View details for DOI 10.1039/d3ta05535c

  View details for Web of Science ID 001136975200001

• Stretchable, recyclable thermosets via photopolymerization and 3D printing of hemiacetal ester-based resins. Chemical science Wu, Y. M., Chyr, G., Park, H., Makar-Limanov, A., Shi, Y., DeSimone, J. M., Bao, Z. 2023; 14 (44): 12535-12540

  Abstract

  Achieving a circular plastics economy is one of our greatest environmental challenges, yet conventional mechanical recycling remains inadequate for thermoplastics and incompatible with thermosets. The next generation of plastic materials will be designed with the capacity for degradation and recycling at end-of-use. To address this opportunity in the burgeoning technologies of 3D printing and photolithography, we report a modular system for the production of degradable and recyclable thermosets via photopolymerization. The polyurethane backbone imparts robust, elastic, and tunable mechanical properties, while the use of hemiacetal ester linkages allows for facile degradation under mild acid. The synthetic design based on hemiacetal esters enables simple purification to regenerate a functional polyurethane diol.

  View details for DOI 10.1039/d3sc03623e

  View details for PubMedID 38020396

  View details for PubMedCentralID PMC10646930

• Degradable semiconducting polymers without long-range order for on-demand degradation of transient electronics JOURNAL OF MATERIALS CHEMISTRY C Chiong, J. A., Michalek, L., Pena-Alcantara, A. E., Ji, X., Schuster, N. J., Bao, Z. 2023

  View details for DOI 10.1039/d3tc03079b

  View details for Web of Science ID 001090295600001

• Gradual Electrical-Double-Layer Modulation in Ion-Polymer Networks for Flexible Pressure Sensors with Wide Dynamic Range ADVANCED FUNCTIONAL MATERIALS Lee, H., Sharma, R., Park, S., Bao, Z., Moon, H., Yoo, S. 2023

  View details for DOI 10.1002/adfm.202302633

  View details for Web of Science ID 001082585200001

• Spiral NeuroString: High-Density Soft Bioelectronic Fibers for Multimodal Sensing and Stimulation. bioRxiv : the preprint server for biology Khatib, M., Zhao, E. T., Wei, S., Abramson, A., Bishop, E. S., Chen, C., Thomas, A., Xu, C., Park, J., Lee, Y., Hamnett, R., Yu, W., Root, S. E., Yuan, L., Chakhtoura, D., Kim, K. K., Zhong, D., Nishio, Y., Zhao, C., Wu, C., Jiang, Y., Zhang, A., Li, J., Wang, W., Salimi-Jazi, F., Rafeeqi, T. A., Hemed, N. M., Tok, J. B., Chen, X., Kaltschmidt, J. A., Dunn, J. C., Bao, Z. 2023

  Abstract

  Bioelectronic fibers hold promise for both research and clinical applications due to their compactness, ease of implantation, and ability to incorporate various functionalities such as sensing and stimulation. However, existing devices suffer from bulkiness, rigidity, limited functionality, and low density of active components. These limitations stem from the difficulty to incorporate many components on one-dimensional (1D) fiber devices due to the incompatibility of conventional microfabrication methods (e.g., photolithography) with curved, thin and long fiber structures. Herein, we introduce a fabrication approach, ‶spiral transformation, to convert two-dimensional (2D) films containing microfabricated devices into 1D soft fibers. This approach allows for the creation of high density multimodal soft bioelectronic fibers, termed Spiral NeuroString (S-NeuroString), while enabling precise control over the longitudinal, angular, and radial positioning and distribution of the functional components. We show the utility of S-NeuroString for motility mapping, serotonin sensing, and tissue stimulation within the dynamic and soft gastrointestinal (GI) system, as well as for single-unit recordings in the brain. The described bioelectronic fibers hold great promises for next-generation multifunctional implantable electronics.

  View details for DOI 10.1101/2023.10.02.560482

  View details for PubMedID 37873341

• Tunable 1D and 2D Polyacrylonitrile Nanosheet Superstructures. ACS nano Gong, H., Patino, D. U., Ilavsky, J., Kuzmenko, I., Peña-Alcántara, A. E., Zhu, C., Coffey, A. H., Michalek, L., Elabd, A., Gao, X., Chen, S., Xu, C., Yan, H., Jiang, Y., Wang, W., Peng, Y., Zeng, Y., Lyu, H., Moon, H., Bao, Z. 2023

  Abstract

  Carbon superstructures are widely applied in energy and environment-related areas. Among them, the flower-like polyacrylonitrile (PAN)-derived carbon materials have shown great promise due to their high surface area, large pore volume, and improved mass transport. In this work, we report a versatile and straightforward method for synthesizing one-dimensional (1D) nanostructured fibers and two-dimensional (2D) nanostructured thin films based on flower-like PAN chemistry by taking advantage of the nucleation and growth behavior of PAN. The resulting nanofibers and thin films exhibited distinct morphologies with intersecting PAN nanosheets, which formed through rapid nucleation on existing PAN. We further constructed a variety of hierarchical PAN superstructures based on different templates, solvents, and concentrations. These PAN nanosheet superstructures can be readily converted to carbon superstructures. As a demonstration, the nanostructured thin film exhibited a contact angle of ∼180° after surface modification with fluoroalkyl monolayers, which is attributed to high surface roughness enabled by the nanosheet assemblies. This study offers a strategy for the synthesis of nanostructured carbon materials for various applications.

  View details for DOI 10.1021/acsnano.3c05792

  View details for PubMedID 37668312

• Colorful low-emissivity paints for space heating and cooling energy savings. Proceedings of the National Academy of Sciences of the United States of America Peng, Y., Lai, J. C., Xiao, X., Jin, W., Zhou, J., Yang, Y., Gao, X., Tang, J., Fan, L., Fan, S., Bao, Z., Cui, Y. 2023; 120 (34): e2300856120

  Abstract

  Space heating and cooling consume ~13% of global energy every year. The development of advanced materials that promote energy savings in heating and cooling is gaining increasing attention. To thermally isolate the space of concern and minimize the heat exchange with the outside environment has been recognized as one effective solution. To this end, here, we develop a universal category of colorful low-emissivity paints to form bilayer coatings consisting of an infrared (IR)-reflective bottom layer and an IR-transparent top layer in colors. The colorful visual appearance ensures the aesthetical effect comparable to conventional paints. High mid-infrared reflectance (up to ~80%) is achieved, which is more than 10 times as conventional paints in the same colors, efficiently reducing both heat gain and loss from/to the outside environment. The high near-IR reflectance also benefits reducing solar heat gain in hot days. The advantageous features of these paints strike a balance between energy savings and penalties for heating and cooling throughout the year, providing a comprehensive year-round energy-saving solution adaptable to a wide variety of climatic zones. Taking a typical midrise apartment building as an example, the application of our colorful low-emissivity paints can realize positive heating, ventilation, and air conditioning energy saving, up to 27.24 MJ/m2/y (corresponding to the 7.4% saving ratio). Moreover, the versatility of the paint, along with its applicability to diverse surfaces of various shapes and materials, makes the paints extensively useful in a range of scenarios, including building envelopes, transportation, and storage.

  View details for DOI 10.1073/pnas.2300856120

  View details for PubMedID 37579165

• Toughening self-healing elastomer crosslinked by metal-ligand coordination through mixed counter anion dynamics. Nature communications Park, H., Kang, T., Kim, H., Kim, J. C., Bao, Z., Kang, J. 2023; 14 (1): 5026

  Abstract

  Mechanically tough and self-healable polymeric materials have found widespread applications in a sustainable future. However, coherent strategies for mechanically tough self-healing polymers are still lacking due to a trade-off relationship between mechanical robustness and viscoelasticity. Here, we disclose a toughening strategy for self-healing elastomers crosslinked by metal-ligand coordination. Emphasis was placed on the effects of counter anions on the dynamic mechanical behaviors of polymer networks. As the coordinating ability of the counter anion increases, the binding of the anion leads to slower dynamics, thus limiting the stretchability and increasing the stiffness. Additionally, multimodal anions that can have diverse coordination modes provide unexpected dynamicity. By simply mixing multimodal and non-coordinating anions, we found a significant synergistic effect on mechanical toughness ( > 3 fold) and self-healing efficiency, which provides new insights into the design of coordination-based tough self-healing polymers.

  View details for DOI 10.1038/s41467-023-40791-z

  View details for PubMedID 37596250

  View details for PubMedCentralID PMC10439188

• Genetically targeted chemical assembly of polymers specifically localized extracellularly to surface membranes of living neurons. Science advances Zhang, A., Loh, K. Y., Kadur, C. S., Michalek, L., Dou, J., Ramakrishnan, C., Bao, Z., Deisseroth, K. 2023; 9 (32): eadi1870

  Abstract

  Multicellular biological systems, particularly living neural networks, exhibit highly complex organization properties that pose difficulties for building cell-specific biocompatible interfaces. We previously developed an approach to genetically program cells to assemble structures that modify electrical properties of neurons in situ, opening up the possibility of building minimally invasive cell-specific structures and interfaces. However, the efficiency and biocompatibility of this approach were challenged by limited membrane targeting of the constructed materials. Here, we design a method for highly localized expression of enzymes targeted to the plasma membrane of primary neurons, with minimal intracellular retention. Next, we show that polymers synthesized in situ by this approach form dense extracellular clusters selectively on the targeted cell membrane and that neurons remain viable after polymerization. Last, we show generalizability of this method across a range of design strategies. This platform can be readily extended to incorporate a broad diversity of materials onto specific cell membranes within tissues and may further enable next-generation biological interfaces.

  View details for DOI 10.1126/sciadv.adi1870

  View details for PubMedID 37556541

• Soft and stretchable organic bioelectronics for continuous intraoperative neurophysiological monitoring during microsurgery. Nature biomedical engineering Zhou, W., Jiang, Y., Xu, Q., Chen, L., Qiao, H., Wang, Y. X., Lai, J. C., Zhong, D., Zhang, Y., Li, W., Du, Y., Wang, X., Lei, J., Dong, G., Guan, X., Ma, S., Kang, P., Yuan, L., Zhang, M., Tok, J. B., Li, D., Bao, Z., Jia, W. 2023

  Abstract

  In microneurosurgery, it is crucial to maintain the structural and functional integrity of the nerve through continuous intraoperative identification of neural anatomy. To this end, here we report the development of a translatable system leveraging soft and stretchable organic-electronic materials for continuous intraoperative neurophysiological monitoring. The system uses conducting polymer electrodes with low impedance and low modulus to record near-field action potentials continuously during microsurgeries, offers higher signal-to-noise ratios and reduced invasiveness when compared with handheld clinical probes for intraoperative neurophysiological monitoring and can be multiplexed, allowing for the precise localization of the target nerve in the absence of anatomical landmarks. Compared with commercial metal electrodes, the neurophysiological monitoring system allowed for enhanced post-operative prognoses after tumour-resection surgeries in rats. Continuous recording of near-field action potentials during microsurgeries may allow for the precise identification of neural anatomy through the entire procedure.

  View details for DOI 10.1038/s41551-023-01069-3

  View details for PubMedID 37537304

  View details for PubMedCentralID 4058457

• Electrolytes with moderate lithium polysulfide solubility for high-performance long-calendar-life lithium-sulfur batteries. Proceedings of the National Academy of Sciences of the United States of America Gao, X., Yu, Z., Wang, J., Zheng, X., Ye, Y., Gong, H., Xiao, X., Yang, Y., Chen, Y., Bone, S. E., Greenburg, L. C., Zhang, P., Su, H., Affeld, J., Bao, Z., Cui, Y. 2023; 120 (31): e2301260120

  Abstract

  Lithium-sulfur (Li-S) batteries with high energy density and low cost are promising for next-generation energy storage. However, their cycling stability is plagued by the high solubility of lithium polysulfide (LiPS) intermediates, causing fast capacity decay and severe self-discharge. Exploring electrolytes with low LiPS solubility has shown promising results toward addressing these challenges. However, here, we report that electrolytes with moderate LiPS solubility are more effective for simultaneously limiting the shuttling effect and achieving good Li-S reaction kinetics. We explored a range of solubility from 37 to 1,100 mM (based on S atom, [S]) and found that a moderate solubility from 50 to 200 mM [S] performed the best. Using a series of electrolyte solvents with various degrees of fluorination, we formulated the Single-Solvent, Single-Salt, Standard Salt concentration with Moderate LiPSs solubility Electrolytes (termed S6MILE) for Li-S batteries. Among the designed electrolytes, Li-S cells using fluorinated-1,2-diethoxyethane S6MILE (F4DEE-S6MILE) showed the highest capacity of 1,160 mAh g-1 at 0.05 C at room temperature. At 60 °C, fluorinated-1,4-dimethoxybutane S6MILE (F4DMB-S6MILE) gave the highest capacity of 1,526 mAh g-1 at 0.05 C and an average CE of 99.89% for 150 cycles at 0.2 C under lean electrolyte conditions. This is a fivefold increase in cycle life compared with other conventional ether-based electrolytes. Moreover, we observed a long calendar aging life, with a capacity increase/recovery of 4.3% after resting for 30 d using F4DMB-S6MILE. Furthermore, the correlation between LiPS solubility, degree of fluorination of the electrolyte solvent, and battery performance was systematically investigated.

  View details for DOI 10.1073/pnas.2301260120

  View details for PubMedID 37487097

• Ion Conducting Polymer Interfaces for Lithium Metal Anodes: Impact on the Electrodeposition Kinetics ADVANCED ENERGY MATERIALS Choudhury, S., Huang, Z., Amanchukwu, C. V., Rudnicki, P. E., Chen, Y., Boyle, D., Qin, J., Cui, Y., Bao, Z. 2023

  View details for DOI 10.1002/aenm.202301899

  View details for Web of Science ID 001038734000001

• Carbon flowers as electrocatalysts for the reduction of oxygen to hydrogen peroxide NANO RESEARCH Gong, H., Wei, L., Chen, S., Chen, Z., Jaramillo, T. F., Bao, Z. 2023

  View details for DOI 10.1007/s12274-023-5903-8

  View details for Web of Science ID 001030509300001

• High-entropy electrolytes for practical lithium metal batteries NATURE ENERGY Kim, S., Wang, J., Xu, R., Zhang, P., Chen, Y., Huang, Z., Yang, Y., Yu, Z., Oyakhire, S. T., Zhang, W., Greenburg, L. C., Kim, M., Boyle, D. T., Sayavong, P., Ye, Y., Qin, J., Bao, Z., Cui, Y. 2023

  View details for DOI 10.1038/s41560-023-01280-1

  View details for Web of Science ID 001023405800005

• An emerging class of carbon materials: Synthesis and applications of carbon flowers MATTER Gong, H., Chen, S., Tok, J., Bao, Z. 2023; 6 (7): 2206-2234

  View details for DOI 10.1016/j.matt.2023.04.027

  View details for Web of Science ID 001040116900001

• Tunable, reusable, and recyclable perfluoropolyether periodic dynamic polymers with high underwater adhesion strength MATTER Nogusa, T., Cooper, C. B., Yu, Z., Zheng, Y., Shi, Y., Bao, Z. 2023; 6 (7): 2439-2453

  View details for DOI 10.1016/j.matt.2023.04.007

  View details for Web of Science ID 001058205700001

• Large-area photo-patterning of initially conductive EGaIn particle-assembled film g for soft electronics MATERIALS TODAY Lee, G., Kim, H., Lee, J., Bae, J., Yang, C., Kim, H., Kang, H., Choi, S. Q., Park, S., Kang, S., Kang, J., Bao, Z., Jeong, J., Park, S. 2023; 67: 84-94

  View details for DOI 10.1016/j.mattod.2023.05.025

  View details for Web of Science ID 001116848200001

• Environmentally stable and stretchable polymer electronics enabled by surface-tethered nanostructured molecular-level protection. Nature nanotechnology Zheng, Y., Michalek, L., Liu, Q., Wu, Y., Kim, H., Sayavong, P., Yu, W., Zhong, D., Zhao, C., Yu, Z., Chiong, J. A., Gong, H., Ji, X., Liu, D., Zhang, S., Prine, N., Zhang, Z., Wang, W., Tok, J. B., Gu, X., Cui, Y., Kang, J., Bao, Z. 2023

  Abstract

  Stretchable polymer semiconductors (PSCs) are essential for soft stretchable electronics. However, their environmental stability remains a longstanding concern. Here we report a surface-tethered stretchable molecular protecting layer to realize stretchable polymer electronics that are stable in direct contact with physiological fluids, containing water, ions and biofluids. This is achieved through the covalent functionalization of fluoroalkyl chains onto a stretchable PSC film surface to form densely packed nanostructures. The nanostructured fluorinated molecular protection layer (FMPL) improves the PSC operational stability over an extended period of 82 days and maintains its protection under mechanical deformation. We attribute the ability of FMPL to block water absorption and diffusion to its hydrophobicity and high fluorination surface density. The protection effect of the FMPL (~6 nm thickness) outperforms various micrometre-thick stretchable polymer encapsulants, leading to a stable PSC charge carrier mobility of ~1 cm2 V-1 s-1 in harsh environments such as in 85-90%-humidity air for 56 days or in water or artificial sweat for 42 days (as a benchmark, the unprotected PSC mobility degraded to 10-6 cm2 V-1 s-1 in the same period). The FMPL also improved the PSC stability against photo-oxidative degradation in air. Overall, we believe that our surface tethering of the nanostructured FMPL is a promising approach to achieve highly environmentally stable and stretchable polymer electronics.

  View details for DOI 10.1038/s41565-023-01418-y

  View details for PubMedID 37322142

• Shear-aligned large-area organic semiconductor crystals through extended pi-pi interaction JOURNAL OF MATERIALS CHEMISTRY C Zhang, S., Talnack, F., Jousselin-Oba, T., Bhat, V., Wu, Y., Lei, Y., Tomo, Y., Gong, H., Michalek, L., Zhong, D., Wu, C., Yassar, A., Mannsfeld, S., Risko, C., Frigoli, M., Bao, Z. 2023

  View details for DOI 10.1039/d3tc01311a

  View details for Web of Science ID 001006838400001

• Autonomous alignment and healing in multilayer soft electronics using immiscible dynamic polymers. Science (New York, N.Y.) Cooper, C. B., Root, S. E., Michalek, L., Wu, S., Lai, J. C., Khatib, M., Oyakhire, S. T., Zhao, R., Qin, J., Bao, Z. 2023; 380 (6648): 935-941

  Abstract

  Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. We fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

  View details for DOI 10.1126/science.adh0619

  View details for PubMedID 37262169

• Dissolution of the Solid Electrolyte Interphase and Its Effects on Lithium Metal Anode Cyclability. Journal of the American Chemical Society Sayavong, P., Zhang, W., Oyakhire, S. T., Boyle, D. T., Chen, Y., Kim, S. C., Vilá, R. A., Holmes, S. E., Kim, M. S., Bent, S. F., Bao, Z., Cui, Y. 2023

  Abstract

  At >95% Coulombic efficiencies, most of the capacity loss for Li metal anodes (LMAs) is through the formation and growth of the solid electrolyte interphase (SEI). However, the mechanism through which this happens remains unclear. One property of the SEI that directly affects its formation and growth is the SEI's solubility in the electrolyte. Here, we systematically quantify and compare the solubility of SEIs derived from ether-based electrolytes optimized for LMAs using in-operando electrochemical quartz crystal microbalance (EQCM). A correlation among solubility, passivity, and cyclability established in this work reveals that SEI dissolution is a major contributor to the differences in passivity and electrochemical performance among battery electrolytes. Together with our EQCM, X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) spectroscopy results, we show that solubility depends on not only the SEI's composition but also the properties of the electrolyte. This provides a crucial piece of information that could help minimize capacity loss due to SEI formation and growth during battery cycling and aging.

  View details for DOI 10.1021/jacs.3c03195

  View details for PubMedID 37220230

• Neuromorphic sensorimotor loop embodied by monolithically integrated, low-voltage, soft e-skin. Science (New York, N.Y.) Wang, W., Jiang, Y., Zhong, D., Zhang, Z., Choudhury, S., Lai, J. C., Gong, H., Niu, S., Yan, X., Zheng, Y., Shih, C. C., Ning, R., Lin, Q., Li, D., Kim, Y. H., Kim, J., Wang, Y. X., Zhao, C., Xu, C., Ji, X., Nishio, Y., Lyu, H., Tok, J. B., Bao, Z. 2023; 380 (6646): 735-742

  Abstract

  Artificial skin that simultaneously mimics sensory feedback and mechanical properties of natural skin holds substantial promise for next-generation robotic and medical devices. However, achieving such a biomimetic system that can seamlessly integrate with the human body remains a challenge. Through rational design and engineering of material properties, device structures, and system architectures, we realized a monolithic soft prosthetic electronic skin (e-skin). It is capable of multimodal perception, neuromorphic pulse-train signal generation, and closed-loop actuation. With a trilayer, high-permittivity elastomeric dielectric, we achieved a low subthreshold swing comparable to that of polycrystalline silicon transistors, a low operation voltage, low power consumption, and medium-scale circuit integration complexity for stretchable organic devices. Our e-skin mimics the biological sensorimotor loop, whereby a solid-state synaptic transistor elicits stronger actuation when a stimulus of increasing pressure is applied.

  View details for DOI 10.1126/science.ade0086

  View details for PubMedID 37200416

• Effects of Transition Metals on Metal-Octaaminophthalocyanine-Based 2D Metal-Organic Frameworks. ACS nano Chen, G., Li, Z., Huang, Z., Lu, H., Long, G., Lezama Pacheco, J. S., Tok, J. B., Gao, T. Z., Lei, Y., Zhou, J., Bao, Z. 2023

  Abstract

  Metal-octaaminophthalocyanine (MOAPc)-based 2D conductive metal-organic frameworks (cMOFs) have shown great potential in several applications, including sensing, energy storage, and electrocatalysis, due to their bimetallic characteristics. Here, we report a detailed metal substitution study on a family of isostructural cMOFs with Co2+, Ni2+, and Cu2+ as both the metal nodes and the metal centers in the MOAPc ligands. We observed that different metal nodes had variations in the reaction kinetics, particle sizes, and crystallinities. Importantly, the electronic structure and conductivity were found to be dependent on both types of metal sites in the 2D cMOFs. Ni-NiOAPc was found to be the most conductive one among the nine possible combinations with a conductivity of 54 ± 4.8 mS/cm. DFT calculations revealed that monolayer Ni-NiOAPc has neither the smallest bandgap nor the highest charge carrier mobility. Hence its highest conductivity stems from its high crystallinity. Collectively, these results provide structure property relationships for MOAPc-based cMOFs with amino coordination units.

  View details for DOI 10.1021/acsnano.3c03143

  View details for PubMedID 37166018

• Understanding Lithium-Ion Dynamics in Single-Ion and Salt-in- Polymer Perfluoropolyethers and Polyethyleneglycol Electrolytes Using Solid-State NMR MACROMOLECULES Amanchukwu, C. V., Gunnarsdottir, A. B., Choudhury, S., Newlove, T. L., Magusin, P. M., Bao, Z., Grey, C. P. 2023

  View details for DOI 10.1021/acs.macromol.2c02160

  View details for Web of Science ID 000984442800001

• A salt-philic, solvent-phobic interfacial coating design for lithium metal electrodes NATURE ENERGY Huang, Z., Lai, J., Liao, S., Yu, Z., Chen, Y., Yu, W., Gong, H., Gao, X., Yang, Y., Qin, J., Cui, Y., Bao, Z. 2023

  View details for DOI 10.1038/s41560-023-01252-5

  View details for Web of Science ID 000975216800001

• Low-voltage polymer transistors on hydrophobic dielectrics and surfaces JOURNAL OF PHYSICS-MATERIALS Kraft, U., Nikolka, M., Wang, G., Kim, Y., Pfattner, R., Alsufyani, M., McCulloch, I., Murmann, B., Bao, Z. 2023; 6 (2)

  View details for DOI 10.1088/2515-7639/acb7a1

  View details for Web of Science ID 000942472000001

• Voltage and Temperature Limits of Advanced Electrolytes for Lithium-Metal Batteries ACS ENERGY LETTERS Buyuker, I., Pei, B., Zhou, H., Cao, X., Yu, Z., Liu, S., Zhang, W., Xu, W., Zhang, J., Bao, Z., Cui, Y., Wang, C., Whittingham, M. 2023: 1735-1743

  View details for DOI 10.1021/acsenergylett.3c00235

  View details for Web of Science ID 000953440200001

• Technology Roadmap for Flexible Sensors. ACS nano Luo, Y., Abidian, M. R., Ahn, J. H., Akinwande, D., Andrews, A. M., Antonietti, M., Bao, Z., Berggren, M., Berkey, C. A., Bettinger, C. J., Chen, J., Chen, P., Cheng, W., Cheng, X., Choi, S. J., Chortos, A., Dagdeviren, C., Dauskardt, R. H., Di, C. A., Dickey, M. D., Duan, X., Facchetti, A., Fan, Z., Fang, Y., Feng, J., Feng, X., Gao, H., Gao, W., Gong, X., Guo, C. F., Guo, X., Hartel, M. C., He, Z., Ho, J. S., Hu, Y., Huang, Q., Huang, Y., Huo, F., Hussain, M. M., Javey, A., Jeong, U., Jiang, C., Jiang, X., Kang, J., Karnaushenko, D., Khademhosseini, A., Kim, D. H., Kim, I. D., Kireev, D., Kong, L., Lee, C., Lee, N. E., Lee, P. S., Lee, T. W., Li, F., Li, J., Liang, C., Lim, C. T., Lin, Y., Lipomi, D. J., Liu, J., Liu, K., Liu, N., Liu, R., Liu, Y., Liu, Y., Liu, Z., Liu, Z., Loh, X. J., Lu, N., Lv, Z., Magdassi, S., Malliaras, G. G., Matsuhisa, N., Nathan, A., Niu, S., Pan, J., Pang, C., Pei, Q., Peng, H., Qi, D., Ren, H., Rogers, J. A., Rowe, A., Schmidt, O. G., Sekitani, T., Seo, D. G., Shen, G., Sheng, X., Shi, Q., Someya, T., Song, Y., Stavrinidou, E., Su, M., Sun, X., Takei, K., Tao, X. M., Tee, B. C., Thean, A. V., Trung, T. Q., Wan, C., Wang, H., Wang, J., Wang, M., Wang, S., Wang, T., Wang, Z. L., Weiss, P. S., Wen, H., Xu, S., Xu, T., Yan, H., Yan, X., Yang, H., Yang, L., Yang, S., Yin, L., Yu, C., Yu, G., Yu, J., Yu, S. H., Yu, X., Zamburg, E., Zhang, H., Zhang, X., Zhang, X., Zhang, X., Zhang, Y., Zhang, Y., Zhao, S., Zhao, X., Zheng, Y., Zheng, Y. Q., Zheng, Z., Zhou, T., Zhu, B., Zhu, M., Zhu, R., Zhu, Y., Zhu, Y., Zou, G., Chen, X. 2023

  Abstract

  Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

  View details for DOI 10.1021/acsnano.2c12606

  View details for PubMedID 36892156

• Data-driven electrolyte design for lithium metal anodes. Proceedings of the National Academy of Sciences of the United States of America Kim, S. C., Oyakhire, S. T., Athanitis, C., Wang, J., Zhang, Z., Zhang, W., Boyle, D. T., Kim, M. S., Yu, Z., Gao, X., Sogade, T., Wu, E., Qin, J., Bao, Z., Bent, S. F., Cui, Y. 2023; 120 (10): e2214357120

  Abstract

  Improving Coulombic efficiency (CE) is key to the adoption of high energy density lithium metal batteries. Liquid electrolyte engineering has emerged as a promising strategy for improving the CE of lithium metal batteries, but its complexity renders the performance prediction and design of electrolytes challenging. Here, we develop machine learning (ML) models that assist and accelerate the design of high-performance electrolytes. Using the elemental composition of electrolytes as the features of our models, we apply linear regression, random forest, and bagging models to identify the critical features for predicting CE. Our models reveal that a reduction in the solvent oxygen content is critical for superior CE. We use the ML models to design electrolyte formulations with fluorine-free solvents that achieve a high CE of 99.70%. This work highlights the promise of data-driven approaches that can accelerate the design of high-performance electrolytes for lithium metal batteries.

  View details for DOI 10.1073/pnas.2214357120

  View details for PubMedID 36848560

• Sensor-enabled Multilayer Artificial Intelligence Analysis for Predictive Wound Healing and Real-Time Patient Monitoring Trotsyuk, A. A., Jing, S., Chen, K., Henn, D., Jiang, Y., Niu, S., Sivaraj, D., Nag, R., Snyder, M., bao, Z., Gurtner, G. C. WILEY. 2023: 268-269

  View details for Web of Science ID 001005693800060

• Interrogation of Wound Healing with Single Cell Analysis using a Wireless Smart Bandage Trotsyuk, A. A., Jiang, Y., Niu, S., Chen, K., Henn, D., Sivaraj, D., Bao, Z., Gurtner, G. C. WILEY. 2023: 270-271

  View details for Web of Science ID 001005693800064

• Controlling the Stem Cell Environment Via Conducting Polymer Hydrogels to Enhance Therapeutic Potential ADVANCED MATERIALS TECHNOLOGIES Santhanam, S., Feig, V. R., McConnell, K. W., Song, S., Gardner, E. E., Patel, J. J., Shan, D., Bao, Z., George, P. M. 2023

  View details for DOI 10.1002/admt.202201724

  View details for Web of Science ID 000940740700001

• A solvent-anchored non-flammable electrolyte MATTER Huang, Z., Lai, J., Kong, X., Rajkovic, I., Xiao, X., Celik, H., Yan, H., Gong, H., Rudnicki, P. E., Lin, Y., Ye, Y., Li, Y., Chen, Y., Gao, X., Jiang, Y., Choudhury, S., Qin, J., Tok, J., Cui, Y., Bao, Z. 2023; 6 (2): 445-459

  View details for DOI 10.1016/j.matt.2022.11.003

  View details for Web of Science ID 001021679000001

• A universal interface for plug-and-play assembly of stretchable devices. Nature Jiang, Y., Ji, S., Sun, J., Huang, J., Li, Y., Zou, G., Salim, T., Wang, C., Li, W., Jin, H., Xu, J., Wang, S., Lei, T., Yan, X., Peh, W. Y., Yen, S. C., Liu, Z., Yu, M., Zhao, H., Lu, Z., Li, G., Gao, H., Liu, Z., Bao, Z., Chen, X. 2023; 614 (7948): 456-462

  Abstract

  Stretchable hybrid devices have enabled high-fidelity implantable1-3 and on-skin4-6 monitoring of physiological signals. These devices typically contain soft modules that match the mechanical requirements in humans7,8 and soft robots9,10, rigid modules containing Si-based microelectronics11,12 and protective encapsulation modules13,14. To make such a system mechanically compliant, the interconnects between the modules need to tolerate stress concentration that may limit their stretching and ultimately cause debonding failure15-17. Here, we report a universal interface that can reliably connect soft, rigid and encapsulation modules together to form robust and highly stretchable devices in a plug-and-play manner. The interface, consisting of interpenetrating polymer and metal nanostructures, connects modules by simply pressing without using pastes. Its formation is depicted by a biphasic network growth model. Soft-soft modules joined by this interface achieved 600% and 180% mechanical and electrical stretchability, respectively. Soft and rigid modules can also be electrically connected using the above interface. Encapsulation on soft modules with this interface is strongly adhesive with an interfacial toughness of 0.24 N mm-1. As a proof of concept, we use this interface to assemble stretchable devices for in vivo neuromodulation and on-skin electromyography, with high signal quality and mechanical resistance. We expect such a plug-and-play interface to simplify and accelerate the development of on-skin and implantable stretchable devices.

  View details for DOI 10.1038/s41586-022-05579-z

  View details for PubMedID 36792740

  View details for PubMedCentralID 4880021

• Revealing the Multifunctions of Li3N in the Suspension Electrolyte for Lithium Metal Batteries. ACS nano Kim, M. S., Zhang, Z., Wang, J., Oyakhire, S. T., Kim, S. C., Yu, Z., Chen, Y., Boyle, D. T., Ye, Y., Huang, Z., Zhang, W., Xu, R., Sayavong, P., Bent, S. F., Qin, J., Bao, Z., Cui, Y. 2023

  Abstract

  Inorganic-rich solid-electrolyte interphases (SEIs) on Li metal anodes improve the electrochemical performance of Li metal batteries (LMBs). Therefore, a fundamental understanding of the roles played by essential inorganic compounds in SEIs is critical to realizing and developing high-performance LMBs. Among the prevalent SEI inorganic compounds observed for Li metal anodes, Li3N is often found in the SEIs of high-performance LMBs. Herein, we elucidate new features of Li3N by utilizing a suspension electrolyte design that contributes to the improved electrochemical performance of the Li metal anode. Through empirical and computational studies, we show that Li3N guides Li electrodeposition along its surface, creates a weakly solvating environment by decreasing Li+-solvent coordination, induces organic-poor SEI on the Li metal anode, and facilitates Li+ transport in the electrolyte. Importantly, recognizing specific roles of SEI inorganics for Li metal anodes can serve as one of the rational guidelines to design and optimize SEIs through electrolyte engineering for LMBs.

  View details for DOI 10.1021/acsnano.2c12470

  View details for PubMedID 36700841

• Effect of Molecular Weight on the Morphology of a Polymer Semiconductor-Thermoplastic Elastomer Blend ADVANCED ELECTRONIC MATERIALS Pena-Alcantara, A., Nikzad, S., Michalek, L., Prine, N., Wang, Y., Gong, H., Ponte, E., Schneider, S., Wu, Y., Root, S. E., He, M., Tok, J., Gu, X., Bao, Z. 2023

  View details for DOI 10.1002/aelm.202201055

  View details for Web of Science ID 000915963500001

• A skin sensor that can rapidly recognize hand-based tasks with limited training NATURE ELECTRONICS Kim, K., Bao, Z. 2023

  View details for DOI 10.1038/s41928-022-00889-6

  View details for Web of Science ID 000909140100001

• High luminescent polymers for stretchable displays. National science review Zhang, Z., Bao, Z. 2023; 10 (1): nwac093

  Abstract

  This perspective summarizes the main approaches to realize stretchable displays with high performance as well as future directions.

  View details for DOI 10.1093/nsr/nwac093

  View details for PubMedID 36684509

  View details for PubMedCentralID PMC9843124

• A substrate-less nanomesh receptor with meta-learning for rapid hand task recognition NATURE ELECTRONICS Kim, K., Kim, M., Pyun, K., Kim, J., Min, J., Koh, S., Root, S. E., Kim, J., Nguyen, B. T., Nishio, Y., Han, S., Choi, J., Kim, C., Tok, J., Jo, S., Ko, S., Bao, Z. 2022

  View details for DOI 10.1038/s41928-022-00888-7

  View details for Web of Science ID 000905510900002

• Healing chronic wounds with a wireless smart bandage with integrated sensors and stimulators NATURE BIOTECHNOLOGY Jiang, Y., Trotsyuk, A. A., Bao, Z. 2022

  View details for DOI 10.1038/s41587-022-01564-z

  View details for Web of Science ID 000887888900004

  View details for PubMedID 36424491

  View details for PubMedCentralID 5350204

• Wireless, closed-loop, smart bandage with integrated sensors and stimulators for advanced wound care and accelerated healing. Nature biotechnology Jiang, Y., Trotsyuk, A. A., Niu, S., Henn, D., Chen, K., Shih, C. C., Larson, M. R., Mermin-Bunnell, A. M., Mittal, S., Lai, J. C., Saberi, A., Beard, E., Jing, S., Zhong, D., Steele, S. R., Sun, K., Jain, T., Zhao, E., Neimeth, C. R., Viana, W. G., Tang, J., Sivaraj, D., Padmanabhan, J., Rodrigues, M., Perrault, D. P., Chattopadhyay, A., Maan, Z. N., Leeolou, M. C., Bonham, C. A., Kwon, S. H., Kussie, H. C., Fischer, K. S., Gurusankar, G., Liang, K., Zhang, K., Nag, R., Snyder, M. P., Januszyk, M., Gurtner, G. C., Bao, Z. 2022

  Abstract

  'Smart' bandages based on multimodal wearable devices could enable real-time physiological monitoring and active intervention to promote healing of chronic wounds. However, there has been limited development in incorporation of both sensors and stimulators for the current smart bandage technologies. Additionally, while adhesive electrodes are essential for robust signal transduction, detachment of existing adhesive dressings can lead to secondary damage to delicate wound tissues without switchable adhesion. Here we overcome these issues by developing a flexible bioelectronic system consisting of wirelessly powered, closed-loop sensing and stimulation circuits with skin-interfacing hydrogel electrodes capable of on-demand adhesion and detachment. In mice, we demonstrate that our wound care system can continuously monitor skin impedance and temperature and deliver electrical stimulation in response to the wound environment. Across preclinical wound models, the treatment group healed ~25% more rapidly and with ~50% enhancement in dermal remodeling compared with control. Further, we observed activation of proregenerative genes in monocyte and macrophage cell populations, which may enhance tissue regeneration, neovascularization and dermal recovery.

  View details for DOI 10.1038/s41587-022-01528-3

  View details for PubMedID 36424488

  View details for PubMedCentralID 5350204

• UV-laser-machined stretchable multi-modal sensor network for soft robot interaction NPJ FLEXIBLE ELECTRONICS Ham, J., Han, A., Cutkosky, M. R., Bao, Z. 2022; 6 (1)

  View details for DOI 10.1038/s41528-022-00225-0

  View details for Web of Science ID 000885316500001

• Investigation of the Structure of Atomically Dispersed NiNx Sites in Ni and N-Doped Carbon Electrocatalysts by 61Ni Mossbauer Spectroscopy and Simulations. Journal of the American Chemical Society Koshy, D. M., Hossain, M. D., Masuda, R., Yoda, Y., Gee, L. B., Abiose, K., Gong, H., Davis, R., Seto, M., Gallo, A., Hahn, C., Bajdich, M., Bao, Z., Jaramillo, T. F. 2022

  Abstract

  Ni and nitrogen-doped carbons are selective catalysts for CO2 reduction to CO (CO2R), but the hypothesized NiNx active sites are challenging to probe with traditional characterization methods. Here, we synthesize 61Ni-enriched model catalysts, termed 61NiPACN, in order to apply 61Ni Mossbauer spectroscopy using synchrotron radiation (61Ni-SR-MS) to characterize the structure of these atomically dispersed NiNx sites. First, we demonstrate that the CO2R results and standard characterization techniques (SEM, PXRD, XPS, XANES, EXAFS) point to the existence of dispersed Ni active sites. Then, 61Ni-SR-MS reveal significant internal magnetic fields of 5.4 T, which is characteristic of paramagnetic, high-spin Ni2+, in the 61NiPACN samples. Finally, theoretical calculations for a variety of Ni-Nx moieties confirm that high-spin Ni2+ is stable in non-planar, tetrahedrally distorted geometries, which results in calculated isotropic hyperfine coupling that is consistent with 61Ni-SR-MS measurements.

  View details for DOI 10.1021/jacs.2c09825

  View details for PubMedID 36394993

• Fast-Charging of Hybrid Lithium-Ion/Lithium-Metal Anodes by Nanostructured Hard Carbon Host ACS ENERGY LETTERS Gong, H., Chen, Y., Chen, S., Xu, C., Yang, Y., Ye, Y., Huang, Z., Ning, R., Cui, Y., Bao, Z. 2022; 7 (12): 4417-4426

  View details for DOI 10.1021/acsenergylett.2c02130

  View details for Web of Science ID 000898367800001

• Tough-interface-enabled stretchable electronics using non-stretchable polymer semiconductors and conductors. Nature nanotechnology Kang, J., Mun, J., Zheng, Y., Koizumi, M., Matsuhisa, N., Wu, H., Chen, S., Tok, J. B., Lee, G. H., Jin, L., Bao, Z. 2022

  Abstract

  Semiconducting polymer thin films are essential elements of soft electronics for both wearable and biomedical applications1-11. However, high-mobility semiconducting polymers are usually brittle and can be easily fractured under small strains (<10%)12-14. Recently, the improved intrinsic mechanical properties of semiconducting polymer films have been reported through molecular design15-18 and nanoconfinement19. Here we show that engineering the interfacial properties between a semiconducting thin film and a substrate can notably delay microcrack formation in the film. We present a universal design strategy that involves covalently bonding a dissipative interfacial polymer layer, consisting of dynamic non-covalent crosslinks, between a semiconducting thin film and a substrate. This enables high interfacial toughness between the layers, suppression of delamination and delocalization of strain. As a result, crack initiation and propagation are notably delayed to much higher strains. Specifically, the crack-onset strain of a high-mobility semiconducting polymer thin film improved from 30% to 110% strain without any noticeable microcracks. Despite the presence of a large mismatch in strain between the plastic semiconducting thin film and elastic substrate after unloading, the tough interface layer helped maintain bonding and exceptional cyclic durability and robustness. Furthermore, we found that our interfacial layer reduces the mismatch of thermal expansion coefficients between the different layers. This approach can improve the crack-onset strain of various semiconducting polymers, conducting polymers and even metal thin films.

  View details for DOI 10.1038/s41565-022-01246-6

  View details for PubMedID 36357793

• Realizing Intrinsically Stretchable Semiconducting Polymer Films by Nontoxic Additives ACS MATERIALS LETTERS Cheng, H., Zhang, S., Michalek, L., Ji, X., Luo, S., Cooper, C. B., Gong, H., Nikzad, S., Chiong, J. A., Wu, Y., Zheng, Y., Liu, Q., Zhong, D., Lei, Y., Tomo, Y., Wei, K., Zhou, D., Tok, J., Bao, Z. 2022; 4 (11): 2328-2336

  View details for DOI 10.1021/acsmaterialslett.2c00749

  View details for Web of Science ID 000898404900001

• Correlating Kinetics to Cyclability Reveals Thermodynamic Origin of Lithium Anode Morphology in Liquid Electrolytes. Journal of the American Chemical Society Boyle, D. T., Kim, S. C., Oyakhire, S. T., Vila, R. A., Huang, Z., Sayavong, P., Qin, J., Bao, Z., Cui, Y. 2022

  Abstract

  The rechargeability of lithium metal batteries strongly depends on the electrolyte. The uniformity of the electroplated Li anode morphology underlies this dependence, so understanding the main drivers of uniform plating is critical for further electrolyte discovery. Here, we correlate electroplating kinetics with cyclability across several classes of electrolytes to reveal the mechanistic influence electrolytes have on morphology. Fast charge-transfer kinetics at fresh Li-electrolyte interfaces correlate well with uniform morphology and cyclability, whereas the resistance of Li+ transport through the solid electrolyte interphase (SEI) weakly correlates with cyclability. These trends contrast with the conventional thought that Li+ transport through the electrolyte or SEI is the main driver of morphological differences between classes of electrolytes. Relating these trends to Li+ solvation, Li nucleation, and the charge-transfer mechanism instead suggests that the Li/Li+ equilibrium potential and the surface energy─thermodynamic factors modulated by the strength of Li+ solvation─underlie electrolyte-dependent trends of Li morphology. Overall, this work provides an insight for discovering functional electrolytes, tuning kinetics in batteries, and explaining why weakly solvating fluorinated electrolytes favor uniform Li plating.

  View details for DOI 10.1021/jacs.2c08182

  View details for PubMedID 36318744

• Grazing-Incidence Texture Tomography and Diffuse Reflectivity Tomography of an Organic Semiconductor Device Array CHEMISTRYMETHODS Smilgies, D., Koker, M. A., Li, R., Shaw, L., Bao, Z. 2022; 2 (11)

  View details for DOI 10.1002/cmtd.202200016

  View details for Web of Science ID 001054528200002

• Stretchable mesh microelectronics for the biointegration and stimulation of human neural organoids. Biomaterials Li, T. L., Liu, Y., Forro, C., Yang, X., Beker, L., Bao, Z., Cui, B., Pașca, S. P. 2022; 290: 121825

  Abstract

  Advances in tridimensional (3D) culture approaches have led to the generation of organoids that recapitulate cellular and physiological features of domains of the human nervous system. Although microelectrodes have been developed for long-term electrophysiological interfaces with neural tissue, studies of long-term interfaces between microelectrodes and free-floating organoids remain limited. In this study, we report a stretchable, soft mesh electrode system that establishes an intimate in vitro electrical interface with human neurons in 3D organoids. Our mesh is constructed with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based electrically conductive hydrogel electrode arrays and elastomeric poly(styrene-ethylene-butylene-styrene) (SEBS) as the substrate and encapsulation materials. This mesh electrode can maintain a stable electrochemical impedance in buffer solution under 50% compressive and 50% tensile strain. We have successfully cultured pluripotent stem cell-derived human cortical organoids (hCO) on this polymeric mesh for more than 3 months and demonstrated that organoids readily integrate with the mesh. Using simultaneous stimulation and calcium imaging, we show that electrical stimulation through the mesh can elicit intensity-dependent calcium signals comparable to stimulation from a bipolar stereotrode. This platform may serve as a tool for monitoring and modulating the electrical activity of in vitro models of neuropsychiatric diseases.

  View details for DOI 10.1016/j.biomaterials.2022.121825

  View details for PubMedID 36326509

• A Hemispherical Image Sensor Array Fabricated with Organic Photo-memory Transistors. Advanced materials (Deerfield Beach, Fla.) Kim, Y., Zhu, C., Lee, W., Smith, A., Ma, H., Li, X., Son, D., Matsuhisa, N., Kim, J., Bae, W., Cho, S. H., Kim, M., Kurosawa, T., Katsumata, T., To, J. W., Oh, J. Y., Paik, S., Kim, S. J., Jin, L., Yan, F., Tok, J. B., Bao, Z. 2022: e2203541

  Abstract

  Hemispherical image sensors simplify lens designs, reduce optical aberrations, and improve image resolution for compact wide-field-of-view cameras. To achieve hemispherical image sensors, organic materials are promising candidates due to the following advantages: tunability of optoelectronic/spectral response and low-temperature low-cost processes. Here, we developed a photolithographic process to prepare a hemispherical image sensor array using organic thin film photo-memory transistors with a density of 308 pixels per square centimeter. Our design includes only one photo-memory transistor as a single active pixel, in contrast to the conventional pixel architecture, consisting of select/readout/reset transistors and a photodiode. Our organic photo-memory transistor, comprising light-sensitive organic semiconductor and charge-trapping dielectric, is able to achieve linear photo-response (light intensity range, from 1 to 50W m-2 ), along with responsivity as high as 1.6 A W-1 (wavelength = 465nm) for a dark current of 0.24 A m-2 (drain voltage = -1.5V). These observed values represent the best responsivity for similar dark currents among all the reported hemispherical image sensor arrays to date. We further developed a transfer method that does not damage organic materials for hemispherical organic photo-memory transistor arrays. Our developed techniques are scalable and are amenable for other high-resolution 3-dimensional organic semiconductor devices. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202203541

  View details for PubMedID 36281793

• Porous Dielectric Elastomer Based Flexible Multiaxial Tactile Sensor for Dexterous Robotic or Prosthetic Hands ADVANCED MATERIALS TECHNOLOGIES Ham, J., Huh, T., Kim, J., Kim, J., Park, S., Cutkosky, M. R., Bao, Z. 2022

  View details for DOI 10.1002/admt.202200903

  View details for Web of Science ID 000869304400001

• Degradation and Speciation of Li Salts during XPS Analysis for Battery Research ACS ENERGY LETTERS Yu, W., Yu, Z., Cui, Y., Bao, Z. 2022; 7 (10): 3270-3275

  View details for DOI 10.1021/acsenergylett.2c01587

  View details for Web of Science ID 000895677900001

• Resolving Current-Dependent Regimes of Electroplating Mechanisms for Fast Charging Lithium Metal Anodes. Nano letters Boyle, D. T., Li, Y., Pei, A., Vila, R. A., Zhang, Z., Sayavong, P., Kim, M. S., Huang, W., Wang, H., Liu, Y., Xu, R., Sinclair, R., Qin, J., Bao, Z., Cui, Y. 2022

  Abstract

  Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li+ transport through the solid electrolyte interphase (SEI) shows that low currents induce plating at buried Li||SEI interfaces, but high currents initiate SEI-breakdown and plating at fresh Li||electrolyte interfaces. The latter pathway can induce uniform growth of {110}-faceted Li at extremely high currents, suggesting ion-transport limitations alone are insufficient to predict Li morphology. At battery relevant fast-charging rates, SEI-breakdown above a critical current density produces detrimental morphology and poor cyclability. Thus, prevention of both SEI-breakdown and slow ion-transport in the electrolyte is essential. This mechanistic insight can inform further electrolyte engineering and customization of fast-charging protocols for Li metal batteries.

  View details for DOI 10.1021/acs.nanolett.2c02792

  View details for PubMedID 36214378

• A flexible electronic strain sensor for the real-time monitoring of tumor regression. Science advances Abramson, A., Chan, C. T., Khan, Y., Mermin-Bunnell, A., Matsuhisa, N., Fong, R., Shad, R., Hiesinger, W., Mallick, P., Gambhir, S. S., Bao, Z. 2022; 8 (37): eabn6550

  Abstract

  Assessing the efficacy of cancer therapeutics in mouse models is a critical step in treatment development. However, low-resolution measurement tools and small sample sizes make determining drug efficacy in vivo a difficult and time-intensive task. Here, we present a commercially scalable wearable electronic strain sensor that automates the in vivo testing of cancer therapeutics by continuously monitoring the micrometer-scale progression or regression of subcutaneously implanted tumors at the minute time scale. In two in vivo cancer mouse models, our sensor discerned differences in tumor volume dynamics between drug- and vehicle-treated tumors within 5 hours following therapy initiation. These short-term regression measurements were validated through histology, and caliper and bioluminescence measurements taken over weeklong treatment periods demonstrated the correlation with longer-term treatment response. We anticipate that real-time tumor regression datasets could help expedite and automate the process of screening cancer therapies in vivo.

  View details for DOI 10.1126/sciadv.abn6550

  View details for PubMedID 36112679

• Formation Mechanism of Flower-like Polyacrylonitrile Particles. Journal of the American Chemical Society Gong, H., Ilavsky, J., Kuzmenko, I., Chen, S., Yan, H., Cooper, C. B., Chen, G., Chen, Y., Chiong, J. A., Jiang, Y., Lai, J., Zheng, Y., Stone, K. H., Huelsenbeck, L., Giri, G., Tok, J. B., Bao, Z. 2022

  Abstract

  Flower-like polyacrylonitrile (PAN) particles have shown promising performance for numerous applications, including sensors, catalysis, and energy storage. However, the detailed formation process of these unique structures during polymerization has not been investigated. Here, we elucidate the formation process of flower-like PAN particles through a series of in situ and ex situ experiments. We have the following key findings. First, lamellar petals within the flower-like particles were predominantly orthorhombic PAN crystals. Second, branching of the lamellae during the particle formation arose from PAN's fast nucleation and growth on pre-existing PAN crystals, which was driven by the poor solubility of PAN in the reaction solvent. Third, the particles were formed to maintain a constant center-to-center distance during the reaction. The separation distance was attributed to strong electrostatic repulsion, which resulted in the final particles' spherical shape and uniform size. Lastly, we employed the understanding of the formation mechanism to tune the PAN particles' morphology using several experimental parameters including incorporating comonomers, changing temperature, adding nucleation seeds, and adjusting the monomer concentration. These findings provide important insights into the bottom-up design of advanced nanostructured PAN-based materials and controlled polymer nanostructure self-assemblies.

  View details for DOI 10.1021/jacs.2c07032

  View details for PubMedID 36102706

• A low-power stretchable neuromorphic nerve with proprioceptive feedback (Aug, 10.1038/s41551022-00918-x, 2022) NATURE BIOMEDICAL ENGINEERING Lee, Y., Liu, Y., Seo, D., Oh, J., Kim, Y., Li, J., Kang, J., Kim, J., Mun, J., Foudeh, A. M., Bao, Z., Lee, T. 2022

  View details for DOI 10.1038/s41551-022-00946-7

  View details for Web of Science ID 000851344700001

  View details for PubMedID 36076076

• Tuning the Mechanical and Electric Properties of Conjugated Polymer Semiconductors: Side-Chain Design Based on Asymmetric Benzodithiophene Building Blocks ADVANCED FUNCTIONAL MATERIALS Liu, D., Lei, Y., Ji, X., Wu, Y., Lin, Y., Wang, Y., Zhang, S., Zheng, Y., Chen, Y., Lai, J., Zhong, D., Cheng, H., Chiong, J. A., Gu, X., Gam, S., Yun, Y., Tok, J., Bao, Z. 2022

  View details for DOI 10.1002/adfm.202203527

  View details for Web of Science ID 000843763400001

• A low-power stretchable neuromorphic nerve with proprioceptive feedback. Nature biomedical engineering Lee, Y., Liu, Y., Seo, D., Oh, J. Y., Kim, Y., Li, J., Kang, J., Kim, J., Mun, J., Foudeh, A. M., Bao, Z., Lee, T. 2022

  Abstract

  By relaying neural signals from the motor cortex to muscles, devices for neurorehabilitation can enhance the movement of limbs in which nerves have been damaged as a consequence of injuries affecting the spinal cord or the lower motor neurons. However, conventional neuroprosthetic devices are rigid and power-hungry. Here we report a stretchable neuromorphic implant that restores coordinated and smooth motions in the legs of mice with neurological motor disorders, enabling the animals to kick a ball, walk or run. The neuromorphic implant acts as an artificial efferent nerve by generating electrophysiological signals from excitatory post-synaptic signals and by providing proprioceptive feedback. The device operates at low power (~1/150 that of a typical microprocessor system), and consists of hydrogel electrodes connected to a stretchable transistor incorporating an organic semiconducting nanowire (acting as an artificial synapse), connected via an ion gel to an artificial proprioceptor incorporating a carbon nanotube strain sensor (acting as an artificial muscle spindle). Stretchable electronics with proprioceptive feedback may inspire the further development of advanced neuromorphic devices for neurorehabilitation.

  View details for DOI 10.1038/s41551-022-00918-x

  View details for PubMedID 35970931

• An X-ray Photoelectron Spectroscopy Primer for Solid Electrolyte Interphase Characterization in Lithium Metal Anodes ACS ENERGY LETTERS Oyakhire, S. T., Gong, H., Cui, Y., Bao, Z., Bent, S. F. 2022; 7 (8)

  View details for DOI 10.1021/acsenergylett.2c01227

  View details for Web of Science ID 000861752900001

• Visualization of the distribution of covalently cross-linked hydrogels in CLARITY brain-polymer hybrids for different monomer concentrations. Scientific reports Malkovskiy, A. V., Tom, A., Joubert, L., Bao, Z. 2022; 12 (1): 13549

  Abstract

  CLARITY is a tissue preservation and optical clearing technique whereby a hydrogel is formed directly within the architectural confines of ex vivo brain tissue. In this work, the extent of polymer gel formation and crosslinking within tissue was assessed using Raman spectroscopy and rheology on CLARITY samples prepared with a range of acrylamide monomer (AAm) concentrations (1%, 4%, 8%, 12% w/v). Raman spectroscopy of individual neurons within hybrids revealed the chemical presence and distribution of polyacrylamide within the mouse hippocampus. Consistent with rheological measurements, lower %AAm concentration decreased shear elastic modulus G', providing a practical correlation with sample permeability and protein retention. Permeability of F(ab)'2 secondary fluorescent antibody changes from 9.3 to 1.4 m2s-1 going from 1 to 12%. Notably, protein retention increased linearly relative to standard PFA-fixed tissue from 96.6% when AAm concentration exceeded 1%, with 12% AAm samples retaining up to~99.3% native protein. This suggests that though 1% AAm offers high permeability, additional %AAm may be required to enhance protein. Our quantitative results on polymer distribution, stability, protein retention, and macromolecule permeability can be used to guide the design of future CLARITY-based tissue-clearing solutions, and establish protocols for characterization of novel tissue-polymer hybrid biomaterials using chemical spectroscopy and rheology.

  View details for DOI 10.1038/s41598-022-17687-x

  View details for PubMedID 35941350

• Using Periodic Dynamic Polymers to Form Supramolecular Nanostructures ACCOUNTS OF MATERIALS RESEARCH Cooper, C. B., Bao, Z. 2022

  View details for DOI 10.1021/accountsmr.2c00101

  View details for Web of Science ID 000837874400001

• A Solution-Processable High-Modulus Crystalline Artificial Solid Electrolyte Interphase for Practical Lithium Metal Batteries ADVANCED ENERGY MATERIALS Yu, Z., Seo, S., Song, J., Zhang, Z., Oyakhire, S. T., Wang, Y., Xu, R., Gong, H., Zhang, S., Zheng, Y., Tsao, Y., Mondonico, L., Lomeli, E. G., Wang, X., Kim, W., Ryu, K., Bao, Z. 2022

  View details for DOI 10.1002/aenm.202201025

  View details for Web of Science ID 000817818300001

• A tissue-like neurotransmitter sensor for the brain and gut. Nature Li, J., Liu, Y., Yuan, L., Zhang, B., Bishop, E. S., Wang, K., Tang, J., Zheng, Y., Xu, W., Niu, S., Beker, L., Li, T. L., Chen, G., Diyaolu, M., Thomas, A., Mottini, V., Tok, J. B., Dunn, J. C., Cui, B., Pașca, S. P., Cui, Y., Habtezion, A., Chen, X., Bao, Z. 2022; 606 (7912): 94-101

  Abstract

  Neurotransmitters play essential roles in regulating neural circuit dynamics both in the central nervous system as well as at the peripheral, including the gastrointestinal tract1-3. Their real-time monitoring will offer critical information for understanding neural function and diagnosing disease1-3. However, bioelectronic tools to monitor the dynamics of neurotransmitters in vivo, especially in the enteric nervous systems, are underdeveloped. This is mainly owing to the limited availability of biosensing tools that are capable of examining soft, complex and actively moving organs. Here we introduce a tissue-mimicking, stretchable, neurochemical biological interface termed NeuroString, which is prepared by laser patterning of a metal-complexed polyimide into an interconnected graphene/nanoparticle network embedded in an elastomer. NeuroString sensors allow chronic in vivo real-time, multichannel and multiplexed monoamine sensing in the brain of behaving mouse, as well as measuring serotonin dynamics in the gut without undesired stimulations and perturbing peristaltic movements. The described elastic and conformable biosensing interface has broad potential for studying the impact of neurotransmitters on gut microbes, brain-gut communication and may ultimately be extended to biomolecular sensing in other soft organs across the body.

  View details for DOI 10.1038/s41586-022-04615-2

  View details for PubMedID 35650358

• High luminescent polymers for stretchable displays NATIONAL SCIENCE REVIEW Zhang, Z., Bao, Z. 2022

  View details for DOI 10.1093/nsr/nwac093

  View details for Web of Science ID 000906751800001

• Enhancing the connection between computation and experiments in electrocatalysis NATURE CATALYSIS Resasco, J., Abild-Pedersen, F., Hahn, C., Bao, Z., Koper, M. M., Jaramillo, T. F. 2022; 5 (5): 374-381

  View details for DOI 10.1038/s41929-022-00789-0

  View details for Web of Science ID 000801852700007

• Tuning Fluorination of Linear Carbonate for Lithium-Ion Batteries JOURNAL OF THE ELECTROCHEMICAL SOCIETY Yu, Z., Yu, W., Chen, Y., Mondonico, L., Xiao, X., Zheng, Y., Liu, F., Hung, S. T., Cui, Y., Bao, Z. 2022; 169 (4)

  View details for DOI 10.1149/1945-7111/ac67f5

  View details for Web of Science ID 000788721400001

• Topological supramolecular network enabled high-conductivity, stretchable organic bioelectronics. Science (New York, N.Y.) Jiang, Y., Zhang, Z., Wang, Y. X., Li, D., Coen, C. T., Hwaun, E., Chen, G., Wu, H. C., Zhong, D., Niu, S., Wang, W., Saberi, A., Lai, J. C., Wu, Y., Wang, Y., Trotsyuk, A. A., Loh, K. Y., Shih, C. C., Xu, W., Liang, K., Zhang, K., Bai, Y., Gurusankar, G., Hu, W., Jia, W., Cheng, Z., Dauskardt, R. H., Gurtner, G. C., Tok, J. B., Deisseroth, K., Soltesz, I., Bao, Z. 2022; 375 (6587): 1411-1417

  Abstract

  Intrinsically stretchable bioelectronic devices based on soft and conducting organic materials have been regarded as the ideal interface for seamless and biocompatible integration with the human body. A remaining challenge is to combine high mechanical robustness with good electrical conduction, especially when patterned at small feature sizes. We develop a molecular engineering strategy based on a topological supramolecular network, which allows for the decoupling of competing effects from multiple molecular building blocks to meet complex requirements. We obtained simultaneously high conductivity and crack-onset strain in a physiological environment, with direct photopatternability down to the cellular scale. We further collected stable electromyography signals on soft and malleable octopus and performed localized neuromodulation down to single-nucleus precision for controlling organ-specific activities through the delicate brainstem.

  View details for DOI 10.1126/science.abj7564

  View details for PubMedID 35324282

• Twisted A-D-A Type Acceptors with Thermally-Activated Delayed Crystallization Behavior for Efficient Nonfullerene Organic Solar Cells ADVANCED ENERGY MATERIALS Wu, Y., Schneider, S., Yuan, Y., Young, R. M., Francese, T., Mansoor, I. F., Dudenas, P. J., Lei, Y., Gomez, E. D., DeLongchamp, D. M., Lipke, M. C., Galli, G., Wasielewski, M. R., Asbury, J. B., Toney, M. F., Bao, Z. 2022

  View details for DOI 10.1002/aenm.202103957

  View details for Web of Science ID 000770786600001

• Liquid electrolyte: The nexus of practical lithium metal batteries JOULE Wang, H., Yu, Z., Kong, X., Kim, S., Boyle, D. T., Qin, J., Bao, Z., Cui, Y. 2022; 6 (3): 588-616

  View details for DOI 10.1016/j.joule.2021.12.018

  View details for Web of Science ID 000773205200008

• Molecular Design of Stretchable Polymer Semiconductors: Current Progress and Future Directions. Journal of the American Chemical Society Zheng, Y., Zhang, S., Tok, J. B., Bao, Z. 2022

  Abstract

  Stretchable polymer semiconductors have advanced rapidly in the past decade as materials required to realize conformable and soft skin-like electronics become available. Through rational molecular-level design, stretchable polymer semiconductor films are now able to retain their electrical functionalities even when subjected to repeated mechanical deformations. Furthermore, their charge-carrier mobilities are on par with the best flexible polymer semiconductors, with some even exceeding that of amorphous silicon. The key advancements are molecular-design concepts that allow multiple strain energy-dissipation mechanisms, while maintaining efficient charge-transport pathways over multiple length scales. In this perspective article, we review recent approaches to confer stretchability to polymer semiconductors while maintaining high charge carrier mobilities, with emphasis on the control of both polymer-chain dynamics and thin-film morphology. Additionally, we present molecular design considerations toward intrinsically elastic semiconductors that are needed for reliable device operation under reversible and repeated deformation. A general approach involving inducing polymer semiconductor nanoconfinement allows for incorporation of several other desired functionalities, such as biodegradability, self-healing, and photopatternability, while enhancing the charge transport. Lastly, we point out future directions, including advancing the fundamental understanding of morphology evolution and its correlation with the change of charge transport under strain, and needs for strain-resilient polymer semiconductors with high mobility retention.

  View details for DOI 10.1021/jacs.2c00072

  View details for PubMedID 35262336

• Reprocessable and Recyclable Polymer Network Electrolytes via Incorporation of Dynamic Covalent Bonds CHEMISTRY OF MATERIALS Lin, Y., Chen, Y., Yu, Z., Huang, Z., Lai, J., Tok, J., Cui, Y., Bao, Z. 2022; 34 (5): 2393-2399

  View details for DOI 10.1021/acs.chemmater.1c04396

  View details for Web of Science ID 000812192800001

• High-brightness all-polymer stretchable LED with charge-trapping dilution. Nature Zhang, Z., Wang, W., Jiang, Y., Wang, Y., Wu, Y., Lai, J., Niu, S., Xu, C., Shih, C., Wang, C., Yan, H., Galuska, L., Prine, N., Wu, H., Zhong, D., Chen, G., Matsuhisa, N., Zheng, Y., Yu, Z., Wang, Y., Dauskardt, R., Gu, X., Tok, J. B., Bao, Z. 2022; 603 (7902): 624-630

  Abstract

  Next-generation light-emitting displays on skin should be soft, stretchable and bright1-7. Previously reported stretchable light-emitting devices were mostly basedon inorganic nanomaterials, such as light-emitting capacitors, quantum dots or perovskites6-11. They either require high operating voltage or have limited stretchability and brightness, resolution or robustness under strain. On the other hand, intrinsically stretchable polymer materials hold the promise of good strain tolerance12,13. However, realizing high brightness remains a grand challenge for intrinsically stretchable light-emitting diodes. Here we report a material design strategy and fabrication processes to achieve stretchable all-polymer-based light-emitting diodes with high brightness (about 7,450candela per square metre), current efficiency (about 5.3candela per ampere) and stretchability (about 100per cent strain). We fabricate stretchable all-polymer light-emitting diodes coloured red, green and blue, achieving both on-skin wireless powering and real-time displaying of pulse signals. This work signifies a considerable advancement towards high-performance stretchable displays.

  View details for DOI 10.1038/s41586-022-04400-1

  View details for PubMedID 35322250

• Bimetallic Nanocatalysts Immobilized in Nanoporous Hydrogels for Long-Term Robust Continuous Glucose Monitoring of Smart Contact Lens. Advanced materials (Deerfield Beach, Fla.) Kim, S., Lee, G., Jeon, C., Han, H. H., Kim, S., Mok, J. W., Joo, C., Shin, S., Sim, J., Myung, D., Bao, Z., Hahn, S. K. 2022: e2110536

  Abstract

  Smart contact lenses for continuous glucose monitoring (CGM) have great potential for huge clinical impact. To date, their development has been limited by challenges in accurate detection of glucose without hysteresis for tear glucose monitoring to track the blood glucose levels. Here, long-term robust CGM in diabetic rabbits is demonstrated by using bimetallic nanocatalysts immobilized in nanoporous hydrogels in smart contact lenses. After redox reaction of glucose oxidase, the nanocatalysts facilitate rapid decomposition of hydrogen peroxide and nanoparticle-mediated charge transfer with drastically improved diffusion via rapid swelling of nanoporous hydrogels. The ocular glucose sensors result in high sensitivity, fast response time, low detection limit, low hysteresis, and rapid sensor warming-up time. In diabetic rabbits, smart contact lens can detect tear glucose levels consistent with blood glucose levels measured by a glucometer and a CGM device, reflecting rapid concentration changes without hysteresis. The CGM in a human demonstrates the feasibility of smart contact lenses for further clinical applications. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202110536

  View details for PubMedID 35194844

• Impact of Molecular Design on Degradation Lifetimes of Degradable Imine-Based Semiconducting Polymers. Journal of the American Chemical Society Chiong, J. A., Zheng, Y., Zhang, S., Ma, G., Wu, Y., Ngaruka, G., Lin, Y., Gu, X., Bao, Z. 2022

  Abstract

  Transient electronics are a rapidly emerging field due to their potential applications in the environment and human health. Recently, a few studies have incorporated acid-labile imine bonds into polymer semiconductors to impart transience; however, understanding of the structure-degradation property relationships of these polymers is limited. In this study, we systematically design and characterize a series of fully degradable diketopyrrolopyrrole-based polymers with engineered sidechains to investigate the impact of several molecular design parameters on the degradation lifetimes of these polymers. By monitoring degradation kinetics via ultraviolet-visible spectroscopy, we reveal that polymer degradation in solution is aggregation-dependent based on the branching point and Mn, with accelerated degradation rates facilitated by decreasing aggregation. Additionally, increasing the hydrophilicity of the polymers promotes water diffusion and therefore acid hydrolysis of the imine bonds along the polymer backbone. The aggregation properties and degradation lifetimes of these polymers rely heavily on solvent, with polymers in chlorobenzene taking six times as long to degrade as in chloroform. We develop a new method for quantifying the degradation of polymers in the thin film and observe that similar factors and considerations (e.g., interchain order, crystallite size, and hydrophilicity) used for designing high-performance semiconductors impact the degradation of imine-based polymer semiconductors. We found that terpolymerization serves as an attractive approach for achieving degradable semiconductors with both good charge transport and tuned degradation properties. This study provides crucial principles for the molecular design of degradable semiconducting polymers, and we anticipate that these findings will expedite progress toward transient electronics with controlled lifetimes.

  View details for DOI 10.1021/jacs.1c12845

  View details for PubMedID 35179880

• Suspension electrolyte with modified Li+ solvation environment for lithium metal batteries. Nature materials Kim, M. S., Zhang, Z., Rudnicki, P. E., Yu, Z., Wang, J., Wang, H., Oyakhire, S. T., Chen, Y., Kim, S. C., Zhang, W., Boyle, D. T., Kong, X., Xu, R., Huang, Z., Huang, W., Bent, S. F., Wang, L., Qin, J., Bao, Z., Cui, Y. 1800

  Abstract

  Designing a stable solid-electrolyte interphase on a Li anode is imperative to developing reliable Li metal batteries. Herein, we report a suspension electrolyte design that modifies the Li+ solvation environment in liquid electrolytes and creates inorganic-rich solid-electrolyte interphases on Li. Li2O nanoparticles suspended in liquid electrolytes were investigated as a proof of concept. Through theoretical and empirical analyses of Li2O suspension electrolytes, the roles played by Li2O in the liquid electrolyte and solid-electrolyte interphases of the Li anode are elucidated. Also, the suspension electrolyte design is applied in conventional and state-of-the-art high-performance electrolytes to demonstrate its applicability. Based on electrochemical analyses, improved Coulombic efficiency (up to ~99.7%), reduced Li nucleation overpotential, stabilized Li interphases and prolonged cycle life of anode-free cells (~70 cycles at 80% of initial capacity) were achieved with the suspension electrolytes. We expect this design principle and our findings to be expanded into developing electrolytes and solid-electrolyte interphases for Li metal batteries.

  View details for DOI 10.1038/s41563-021-01172-3

  View details for PubMedID 35039645

• Rational solvent molecule tuning for high-performance lithium metal battery electrolytes NATURE ENERGY Yu, Z., Rudnicki, P. E., Zhang, Z., Huang, Z., Celik, H., Oyakhire, S. T., Chen, Y., Kong, X., Kim, S., Xiao, X., Wang, H., Zheng, Y., Kamat, G. A., Kim, M., Bent, S. F., Qin, J., Cui, Y., Bao, Z. 2022

  View details for DOI 10.1038/s41560-021-00962-y

  View details for Web of Science ID 000742253900001

• Capturing the swelling of solid-electrolyte interphase in lithium metal batteries. Science (New York, N.Y.) Zhang, Z., Li, Y., Xu, R., Zhou, W., Li, Y., Oyakhire, S. T., Wu, Y., Xu, J., Wang, H., Yu, Z., Boyle, D. T., Huang, W., Ye, Y., Chen, H., Wan, J., Bao, Z., Chiu, W., Cui, Y. 1800; 375 (6576): 66-70

  Abstract

  [Figure: see text].

  View details for DOI 10.1126/science.abi8703

  View details for PubMedID 34990230

• Effects of Polymer Coating Mechanics at Solid-Electrolyte Interphase for Stabilizing Lithium Metal Anodes ADVANCED ENERGY MATERIALS Huang, Z., Choudhury, S., Paul, N., Thienenkamp, J., Lennartz, P., Gong, H., Muller-Buschbaum, P., Brunklaus, G., Gilles, R., Bao, Z. 2021

  View details for DOI 10.1002/aenm.202103187

  View details for Web of Science ID 000732690000001

• Editorial for the special issue of Materials Horizons in honor of Seth Marder. Materials horizons Bredas, J., Bao, Z., Nguyen, T., Thompson, M. E. 1800

  View details for DOI 10.1039/d1mh90068d

  View details for PubMedID 34918014

• A soft-electronic sensor network tracks neuromotor development in infants. Proceedings of the National Academy of Sciences of the United States of America Khan, Y., Bao, Z. 2021; 118 (46)

  View details for DOI 10.1073/pnas.2116943118

  View details for PubMedID 34772819

• Steric Effect Tuned Ion Solvation Enabling Stable Cycling of High-Voltage Lithium Metal Battery. Journal of the American Chemical Society Chen, Y., Yu, Z., Rudnicki, P., Gong, H., Huang, Z., Kim, S. C., Lai, J., Kong, X., Qin, J., Cui, Y., Bao, Z. 2021

  Abstract

  1,2-Dimethoxyethane (DME) is a common electrolyte solvent for lithium metal batteries. Various DME-based electrolyte designs have improved long-term cyclability of high-voltage full cells. However, insufficient Coulombic efficiency at the Li anode and poor high-voltage stability remain a challenge for DME electrolytes. Here, we report a molecular design principle that utilizes a steric hindrance effect to tune the solvation structures of Li+ ions. We hypothesized that by substituting the methoxy groups on DME with larger-sized ethoxy groups, the resulting 1,2-diethoxyethane (DEE) should have a weaker solvation ability and consequently more anion-rich inner solvation shells, both of which enhance interfacial stability at the cathode and anode. Experimental and computational evidence indicates such steric-effect-based design leads to an appreciable improvement in electrochemical stability of lithium bis(fluorosulfonyl)imide (LiFSI)/DEE electrolytes. Under stringent full-cell conditions of 4.8 mAh cm-2 NMC811, 50 mum thin Li, and high cutoff voltage at 4.4 V, 4 M LiFSI/DEE enabled 182 cycles until 80% capacity retention while 4 M LiFSI/DME only achieved 94 cycles. This work points out a promising path toward the molecular design of non-fluorinated ether-based electrolyte solvents for practical high-voltage Li metal batteries.

  View details for DOI 10.1021/jacs.1c09006

  View details for PubMedID 34709034

• High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures. ACS central science Cooper, C. B., Nikzad, S., Yan, H., Ochiai, Y., Lai, J., Yu, Z., Chen, G., Kang, J., Bao, Z. 2021; 7 (10): 1657-1667

  Abstract

  Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to 1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers.

  View details for DOI 10.1021/acscentsci.1c00829

  View details for PubMedID 34729409

• All-Solid-State Lithium-Sulfur Batteries Enhanced by Redox Mediators. Journal of the American Chemical Society Gao, X., Zheng, X., Tsao, Y., Zhang, P., Xiao, X., Ye, Y., Li, J., Yang, Y., Xu, R., Bao, Z., Cui, Y. 2021

  Abstract

  Redox mediators (RMs) play a vital role in some liquid electrolyte-based electrochemical energy storage systems. However, the concept of redox mediator in solid-state batteries remains unexplored. Here, we selected a group of RM candidates and investigated their behaviors and roles in all-solid-state lithium-sulfur batteries (ASSLSBs). The soluble-type quinone-based RM (AQT) shows the most favorable redox potential and the best redox reversibility that functions well for lithium sulfide (Li2S) oxidation in solid polymer electrolytes. Accordingly, Li2S cathodes with AQT RMs present a significantly reduced energy barrier (average oxidation potential of 2.4 V) during initial charging at 0.1 C at 60 °C and the following discharge capacity of 1133 mAh gs-1. Using operando sulfur K-edge X-ray absorption spectroscopy, we directly tracked the sulfur speciation in ASSLSBs and proved that the solid-polysulfide-solid reaction of Li2S cathodes with RMs facilitated Li2S oxidation. In contrast, for bare Li2S cathodes, the solid-solid Li2S-sulfur direct conversion in the first charge cycle results in a high energy barrier for activation (charge to 4 V) and low sulfur utilization. The Li2S@AQT cell demonstrates superior cycling stability (average Coulombic efficiency 98.9% for 150 cycles) and rate capability owing to the effective AQT-enhanced Li-S reaction kinetics. This work reveals the evolution of sulfur species in ASSLSBs and realizes the fast Li-S reaction kinetics by designing an effective sulfur speciation pathway.

  View details for DOI 10.1021/jacs.1c07754

  View details for PubMedID 34677957

• A molecular design approach towards elastic and multifunctional polymer electronics. Nature communications Zheng, Y., Yu, Z., Zhang, S., Kong, X., Michaels, W., Wang, W., Chen, G., Liu, D., Lai, J., Prine, N., Zhang, W., Nikzad, S., Cooper, C. B., Zhong, D., Mun, J., Zhang, Z., Kang, J., Tok, J. B., McCulloch, I., Qin, J., Gu, X., Bao, Z. 2021; 12 (1): 5701

  Abstract

  Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facilepatternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C-H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V-1 s-1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics.

  View details for DOI 10.1038/s41467-021-25719-9

  View details for PubMedID 34588448

• Modular Synthesis of Fully Degradable Imine-Based Semiconducting p-Type and n-Type Polymers CHEMISTRY OF MATERIALS Tran, H., Nikzad, S., Chiong, J. A., Schuster, N. J., Pena-Alcantara, A. E., Feig, V. R., Zheng, Y., Bao, Z. 2021; 33 (18): 7465-7474

  View details for DOI 10.1021/acs.chemmater.1c02258

  View details for Web of Science ID 000703532600031

• Post-surgical wireless monitoring of arterial health progression. iScience Ruth, S. R., Kim, M., Oda, H., Wang, Z., Khan, Y., Chang, J., Fox, P. M., Bao, Z. 2021; 24 (9): 103079

  Abstract

  Early detection of limb ischemia, strokes, and heart attacks may be enabled via long-term monitoring of arterial health. Early stenosis, decreased blood flow, and clots are common after surgical vascular bypass or plaque removal from a diseased vessel and can lead to the above diseases. Continuous arterial monitoring for the early diagnosis of such complications is possible by implanting a sensor during surgery that is wirelessly monitored by patients after surgery. Here, we report the design of a wireless capacitive sensor wrapped around the artery during surgery for continuous post-operative monitoring of arterial health. The sensor responds to diverse artery sizes and extents of occlusion invitro to at least 20cm upstream and downstream of the sensor. It demonstrated strong capability to monitor progression of arterial occlusion in human cadaver and small animal models. This technology is promising for wireless monitoring of arterial health for pre-symptomatic disease detection and prevention.

  View details for DOI 10.1016/j.isci.2021.103079

  View details for PubMedID 34568798

• Chemical Modifications of Ag Catalyst Surfaces with Imidazolium Ionomers Modulate H2 Evolution Rates during Electrochemical CO2 Reduction. Journal of the American Chemical Society Koshy, D. M., Akhade, S. A., Shugar, A., Abiose, K., Shi, J., Liang, S., Oakdale, J. S., Weitzner, S. E., Varley, J. B., Duoss, E. B., Baker, S. E., Hahn, C., Bao, Z., Jaramillo, T. F. 2021

  Abstract

  Bridging polymer design with catalyst surface science is a promising direction for tuning and optimizing electrochemical reactors that could impact long-term goals in energy and sustainability. Particularly, the interaction between inorganic catalyst surfaces and organic-based ionomers provides an avenue to both steer reaction selectivity and promote activity. Here, we studied the role of imidazolium-based ionomers for electrocatalytic CO2 reduction to CO (CO2R) on Ag surfaces and found that they produce no effect on CO2R activity yet strongly promote the competing hydrogen evolution reaction (HER). By examining the dependence of HER and CO2R rates on concentrations of CO2 and HCO3-, we developed a kinetic model that attributes HER promotion to intrinsic promotion of HCO3- reduction by imidazolium ionomers. We also show that varying the ionomer structure by changing substituents on the imidazolium ring modulates the HER promotion. This ionomer-structure dependence was analyzed via Taft steric parameters and density functional theory calculations, which suggest that steric bulk from functionalities on the imidazolium ring reduces access of the ionomer to both HCO3- and the Ag surface, thus limiting the promotional effect. Our results help develop design rules for ionomer-catalyst interactions in CO2R and motivate further work into precisely uncovering the interplay between primary and secondary coordination in determining electrocatalytic behavior.

  View details for DOI 10.1021/jacs.1c06212

  View details for PubMedID 34472346

• Masthead: (Adv. Mater. 35/2021) ADVANCED MATERIALS Aizenberg, J., Ariga, K., Bao, Z., Chen, X., Feng, X., Hyeon, T., Liu, B. 2021; 33 (35)

  View details for DOI 10.1002/adma.202170273

  View details for Web of Science ID 000692195500028

• Advancing models of neural development with biomaterials. Nature reviews. Neuroscience Roth, J. G., Huang, M. S., Li, T. L., Feig, V. R., Jiang, Y., Cui, B., Greely, H. T., Bao, Z., Pasca, S. P., Heilshorn, S. C. 2021

  Abstract

  Human pluripotent stem cells have emerged as a promising in vitro model system for studying the brain. Two-dimensional and three-dimensional cell culture paradigms have provided valuable insights into the pathogenesis of neuropsychiatric disorders, but they remain limited in their capacity to model certain features of human neural development. Specifically, current models do not efficiently incorporate extracellular matrix-derived biochemical and biophysical cues, facilitate multicellular spatio-temporal patterning, or achieve advanced functional maturation. Engineered biomaterials have the capacity to create increasingly biomimetic neural microenvironments, yet further refinement is needed before these approaches are widely implemented. This Review therefore highlights how continued progression and increased integration of engineered biomaterials may be well poised to address intractable challenges in recapitulating human neural development.

  View details for DOI 10.1038/s41583-021-00496-y

  View details for PubMedID 34376834

• Controlling Polymer Morphology in Blade-Coated All-Polymer Solar Cells CHEMISTRY OF MATERIALS Schneider, S. A., Gu, K. L., Yan, H., Abdelsamie, M., Bao, Z., Toney, M. F. 2021; 33 (15): 5951-5961

  View details for DOI 10.1021/acs.chemmater.1c01050

  View details for Web of Science ID 000685206200013

• A Nickel-Decorated Carbon Flower/Sulfur Cathode for Lean-Electrolyte Lithium-Sulfur Batteries ADVANCED ENERGY MATERIALS Tsao, Y., Gong, H., Chen, S., Chen, G., Liu, Y., Gao, T. Z., Cui, Y., Bao, Z. 2021

  View details for DOI 10.1002/aenm.202101449

  View details for Web of Science ID 000681202600001

• A Design Strategy for Intrinsically Stretchable High-Performance Polymer Semiconductors: Incorporating Conjugated Rigid Fused-Rings with Bulky Side Groups. Journal of the American Chemical Society Liu, D., Mun, J., Chen, G., Schuster, N. J., Wang, W., Zheng, Y., Nikzad, S., Lai, J., Wu, Y., Zhong, D., Lin, Y., Lei, Y., Chen, Y., Gam, S., Chung, J. W., Yun, Y., Tok, J. B., Bao, Z. 2021

  Abstract

  Strategies to improve stretchability of polymer semiconductors, such as introducing flexible conjugation-breakers or adding flexible blocks, usually result in degraded electrical properties. In this work, we propose a concept to address this limitation, by introducing conjugated rigid fused-rings with optimized bulky side groups and maintaining a conjugated polymer backbone. Specifically, we investigated two classes of rigid fused-ring systems, namely, benzene-substituted dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (Ph-DBTTT) and indacenodithiophene (IDT) systems, and identified molecules displaying optimized electrical and mechanical properties. In the IDT system, the polymer PIDT-3T-OC12-10% showed promising electrical and mechanical properties. In fully stretchable transistors, the polymer PIDT-3T-OC12-10% showed a mobility of 0.27 cm2 V-1 s-1 at 75% strain and maintained its mobility after being subjected to hundreds of stretching-releasing cycles at 25% strain. Our results underscore the intimate correlation between chemical structures, mechanical properties, and charge carrier mobility for polymer semiconductors. Our described molecular design approach will help to expedite the next generation of intrinsically stretchable high-performance polymer semiconductors.

  View details for DOI 10.1021/jacs.1c04984

  View details for PubMedID 34284578

• Entrepreneurship in Polymer Chemistry. ACS macro letters Knauer, K. M., Speros, J. C., Kemp, L. K., Savin, D. A., Bao, Z., Coates, G. W., Epps, T. H., Hawker, C. J., Le Roy, J. J., Morse, M., Yu, O. 2021; 10 (7): 864-872

  Abstract

  Launching a startup company is like synthesizing a new molecule. There is a starting point and a general concept for how to achieve the desired end. Known steps may be taken, but a successful synthesis is rarely the result of the original plan and relies on perseverance and creativity. If done well, the starting molecule (idea) gives rise to a new final product (business). Having personally lived these journeys, the authors of this viewpoint distilled their combined experiences into relevant topics for scientific entrepreneurs. This viewpoint is not a how-to guide for launching a startup. Instead, relatable personal insights and potential best practices are shared to catalyze discussions around a topic of growing relevance to both the polymer community and workforce of the future.

  View details for DOI 10.1021/acsmacrolett.1c00303

  View details for PubMedID 35549209

• Entrepreneurship in Polymer Chemistry ACS MACRO LETTERS Knauer, K. M., Speros, J. C., Kemp, L. K., Savin, D. A., Bao, Z., Coates, G. W., Epps, T. H., Hawker, C. J., Le Roy, J. J., Morse, M., Yu, O. 2021; 10 (7): 864-872

  View details for DOI 10.1021/acsmacrolett.1c00303

  View details for Web of Science ID 000677482700016

• Potentiometric Measurement to Probe Solvation Energy and Its Correlation to Lithium Battery Cyclability. Journal of the American Chemical Society Kim, S. C., Kong, X., Vila, R. A., Huang, W., Chen, Y., Boyle, D. T., Yu, Z., Wang, H., Bao, Z., Qin, J., Cui, Y. 2021

  Abstract

  The electrolyte plays a critical role in lithium-ion batteries, as it impacts almost every facet of a battery's performance. However, our understanding of the electrolyte, especially solvation of Li+, lags behind its significance. In this work, we introduce a potentiometric technique to probe the relative solvation energy of Li+ in battery electrolytes. By measuring open circuit potential in a cell with symmetric electrodes and asymmetric electrolytes, we quantitatively characterize the effects of concentration, anions, and solvents on solvation energy across varied electrolytes. Using the technique, we establish a correlation between cell potential (Ecell) and cyclability of high-performance electrolytes for lithium metal anodes, where we find that solvents with more negative cell potentials and positive solvation energies-those weakly binding to Li+-lead to improved cycling stability. Cryogenic electron microscopy reveals that weaker solvation leads to an anion-derived solid-electrolyte interphase that stabilizes cycling. Using the potentiometric measurement for characterizing electrolytes, we establish a correlation that can guide the engineering of effective electrolytes for the lithium metal anode.

  View details for DOI 10.1021/jacs.1c03868

  View details for PubMedID 34184873

• A design strategy for high mobility stretchable polymer semiconductors. Nature communications Mun, J., Ochiai, Y., Wang, W., Zheng, Y., Zheng, Y., Wu, H., Matsuhisa, N., Higashihara, T., Tok, J. B., Yun, Y., Bao, Z. 2021; 12 (1): 3572

  Abstract

  As a key component in stretchable electronics, semiconducting polymers have been widely studied. However, it remains challenging to achieve stretchable semiconducting polymers with high mobility and mechanical reversibility against repeated mechanical stress. Here, we report a simple and universal strategy to realize intrinsically stretchable semiconducting polymers with controlled multi-scale ordering to address this challenge. Specifically, incorporating two types of randomly distributed co-monomer units reduces overall crystallinity and longer-range orders while maintaining short-range ordered aggregates. The resulting polymers maintain high mobility while having much improved stretchability and mechanical reversibility compared with the regular polymer structure with only one type of co-monomer units. Interestingly, the crystalline microstructures are mostly retained even under strain, which may contribute to the improved robustness of our stretchable semiconductors. The proposed molecular design concept is observed to improve the mechanical properties of various p- and n-type conjugated polymers, thus showing the general applicability of our approach. Finally, fully stretchable transistors fabricated with our newly designed stretchable semiconductors exhibit the highest and most stable mobility retention capability under repeated strains of 1,000 cycles. Our general molecular engineering strategy offers a rapid way to develop high mobility stretchable semiconducting polymers.

  View details for DOI 10.1038/s41467-021-23798-2

  View details for PubMedID 34117254

• Conducting polymer-based granular hydrogels for injectable 3D cell scaffolds. Advanced materials technologies Feig, V. R., Santhanam, S., McConnell, K. W., Liu, K., Azadian, M., Brunel, L. G., Huang, Z., Tran, H., George, P. M., Bao, Z. 2021; 6 (6)

  Abstract

  Injectable 3D cell scaffolds possessing both electrical conductivity and native tissue-level softness would provide a platform to leverage electric fields to manipulate stem cell behavior. Granular hydrogels, which combine jamming-induced elasticity with repeatable injectability, are versatile materials to easily encapsulate cells to form injectable 3D niches. In this work, we demonstrate that electrically conductive granular hydrogels can be fabricated via a simple method involving fragmentation of a bulk hydrogel made from the conducting polymer PEDOT:PSS. These granular conductors exhibit excellent shear-thinning and self-healing behavior, as well as record-high electrical conductivity for an injectable 3D scaffold material (~10 S m-1). Their granular microstructure also enables them to easily encapsulate induced pluripotent stem cell (iPSC)-derived neural progenitor cells, which were viable for at least 5 days within the injectable gel matrices. Finally, we demonstrate gel biocompatibility with minimal observed inflammatory response when injected into a rodent brain.

  View details for DOI 10.1002/admt.202100162

  View details for PubMedID 34179344

  View details for PubMedCentralID PMC8225239

• Standalone real-time health monitoring patch based on a stretchable organic optoelectronic system. Science advances Lee, Y., Chung, J. W., Lee, G. H., Kang, H., Kim, J., Bae, C., Yoo, H., Jeong, S., Cho, H., Kang, S., Jung, J. Y., Lee, D., Gam, S., Hahm, S. G., Kuzumoto, Y., Kim, S. J., Bao, Z., Hong, Y., Yun, Y., Kim, S. 2021; 7 (23)

  Abstract

  Skin-like health care patches (SHPs) are next-generation health care gadgets that will enable seamless monitoring of biological signals in daily life. Skin-conformable sensors and a stretchable display are critical for the development of standalone SHPs that provide real-time information while alleviating privacy concerns related to wireless data transmission. However, the production of stretchable wearable displays with sufficient pixels to display this information remains challenging. Here, we report a standalone organic SHP that provides real-time heart rate information. The 15-mum-thick SHP comprises a stretchable organic light-emitting diode display and stretchable organic photoplethysmography (PPG) heart rate sensor on all-elastomer substrate and operates stably under 30% strain using a combination of stress relief layers and deformable micro-cracked interconnects that reduce the mechanical stress on the active optoelectronic components. This approach provides a rational strategy for high-resolution stretchable displays, enabling the production of ideal platforms for next-generation wearable health care electronics.

  View details for DOI 10.1126/sciadv.abg9180

  View details for PubMedID 34088675

• Integrating Emerging Polymer Chemistries for the Advancement of Recyclable, Biodegradable, and Biocompatible Electronics. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Chiong, J. A., Tran, H., Lin, Y., Zheng, Y., Bao, Z. 2021: e2101233

  Abstract

  Through advances in molecular design, understanding of processing parameters, and development of non-traditional device fabrication techniques, the field of wearable and implantable skin-inspired devices is rapidly growing interest in the consumer market. Like previous technological advances, economic growth and efficiency is anticipated, as these devices will enable an augmented level of interaction between humans and the environment. However, the parallel growing electronic waste that is yet to be addressed has already left an adverse impact on the environment and human health. Looking forward, it is imperative to develop both human- and environmentally-friendly electronics, which are contingent on emerging recyclable, biodegradable, and biocompatible polymer technologies. This review provides definitions for recyclable, biodegradable, and biocompatible polymers based on reported literature, an overview of the analytical techniques used to characterize mechanical and chemical property changes, and standard policies for real-life applications. Then, various strategies in designing the next-generation of polymers to be recyclable, biodegradable, or biocompatible with enhanced functionalities relative to traditional or commercial polymers are discussed. Finally, electronics that exhibit an element of recyclability, biodegradability, or biocompatibility with new molecular design are highlighted with the anticipation of integrating emerging polymer chemistries into future electronic devices.

  View details for DOI 10.1002/advs.202101233

  View details for PubMedID 34014619

• Dual-Solvent Li-Ion Solvation Enables High-Performance Li-Metal Batteries ADVANCED MATERIALS Wang, H., Yu, Z., Kong, X., Huang, W., Zhang, Z., Mackanic, D. G., Huang, X., Qin, J., Bao, Z., Cui, Y. 2021: e2008619

  Abstract

  Novel electrolyte designs to further enhance the lithium (Li) metal battery cyclability are highly desirable. Here, fluorinated 1,6-dimethoxyhexane (FDMH) is designed and synthesized as the solvent molecule to promote electrolyte stability with its prolonged -CF2 - backbone. Meanwhile, 1,2-dimethoxyethane is used as a co-solvent to enable higher ionic conductivity and much reduced interfacial resistance. Combining the dual-solvent system with 1 m lithium bis(fluorosulfonyl)imide (LiFSI), high Li-metal Coulombic efficiency (99.5%) and oxidative stability (6 V) are achieved. Using this electrolyte, 20 µm Li||NMC batteries are able to retain ≈80% capacity after 250 cycles and Cu||NMC anode-free pouch cells last 120 cycles with 75% capacity retention under ≈2.1 µL mAh-1 lean electrolyte conditions. Such high performances are attributed to the anion-derived solid-electrolyte interphase, originating from the coordination of Li-ions to the highly stable FDMH and multiple anions in their solvation environments. This work demonstrates a new electrolyte design strategy that enables high-performance Li-metal batteries with multisolvent Li-ion solvation with rationally optimized molecular structure and ratio.

  View details for DOI 10.1002/adma.202008619

  View details for Web of Science ID 000648495100001

  View details for PubMedID 33969571

• Conjugated Polymer for Implantable Electronics toward Clinical Application. Advanced healthcare materials Liu, Y., Feig, V. R., Bao, Z. 2021: e2001916

  Abstract

  Owing to their excellent mechanical flexibility, mixed-conducting electrical property, and extraordinary chemical turnability, conjugated polymers have been demonstrated to be an ideal bioelectronic interface to deliver therapeutic effect in many different chronic diseases. This review article summarizes the latest advances in implantable electronics using conjugated polymers as electroactive materials and identifies remaining challenges and opportunities for developing electronic medicine. Examples of conjugated polymer-based bioelectronic devices are selectively reviewed in human clinical studies or animal studies with the potential for clinical adoption. The unique properties of conjugated polymers are highlighted and exemplified as potential solutions to address the specific challenges in electronic medicine.

  View details for DOI 10.1002/adhm.202001916

  View details for PubMedID 33899347

• Conducting Polymer-Based Granular Hydrogels for Injectable 3D Cell Scaffolds ADVANCED MATERIALS TECHNOLOGIES Feig, V., Santhanam, S., McConnell, K., Liu, K., Azadian, M., Brunel, L., Huang, Z., Tran, H., George, P. M., Bao, Z. 2021

  View details for DOI 10.1002/admt.202100162

  View details for Web of Science ID 000643417600001

• Bridging thermal catalysis and electrocatalysis: Catalyzing CO2 conversion with carbon-based materials. Angewandte Chemie (International ed. in English) Koshy, D., Nathan, S., Asundi, A., Abdellah, A., Dull, S., Cullen, D., Higgins, D., Bao, Z., Bent, S., Jaramillo, T. 2021

  Abstract

  Understanding the differences between reactions driven by elevated temperature or electric potential remains challenging, largely due to materials incompatibilities between thermal catalytic and electrocatalytic environments. We show that Ni, N-doped carbon (NiPACN), an electrocatalyst for the reduction of CO2 to CO (CO2R), can also selectively catalyze thermal CO2 to CO via the reverse water gas shift (RWGS) representing a direct analogy between catalytic phenomena across the two reaction environments. Advanced characterization techniques reveal that NiPACN likely facilitates RWGS on dispersed Ni sites in agreement with CO2R active site studies. Finally, we construct a generalized reaction driving-force that includes temperature and potential and suggest that NiPACN could facilitate faster kinetics in CO2R relative to RWGS due to lower intrinsic barriers. This report motivates further studies that quantitatively link catalytic phenomena across disparate reaction environments.

  View details for DOI 10.1002/anie.202101326

  View details for PubMedID 33823079

• Corrosion of lithium metal anodes during calendar ageing and its microscopic origins NATURE ENERGY Boyle, D. T., Huang, W., Wang, H., Li, Y., Chen, H., Yu, Z., Zhang, W., Bao, Z., Cui, Y. 2021

  View details for DOI 10.1038/s41560-021-00787-9

  View details for Web of Science ID 000631480700002

• Ultra-Compliant and Tough Thermochromic Polymer for Self-Regulated Smart Windows ADVANCED FUNCTIONAL MATERIALS Zhang, Q., Jiang, Y., Chen, L., Chen, W., Li, J., Cai, Y., Ma, C., Xu, W., Lu, Y., Jia, X., Bao, Z. 2021

  View details for DOI 10.1002/adfm.202100686

  View details for Web of Science ID 000621942700001

• Manipulation and statistical analysis of the fluid flow of polymer semiconductor solutions during meniscus-guided coatin MRS BULLETIN Shaw, L., Diao, Y., Martin-Noble, G. C., Yan, H., Hayoz, P., Weitz, T., Kaelblein, D., Toney, M. F., Bao, Z. 2021

  View details for DOI 10.1557/s43577-021-00049-9

  View details for Web of Science ID 000621322100001

• Efficient Lithium Metal Cycling over a Wide Range of Pressures from an Anion-Derived Solid-Electrolyte Interphase Framework ACS ENERGY LETTERS Wang, H., Huang, W., Yu, Z., Huang, W., Xu, R., Zhang, Z., Bao, Z., Cui, Y. 2021; 6 (2): 816–25

  View details for DOI 10.1021/acsenergylett.0c02533

  View details for Web of Science ID 000619803400061

• Flexible Fringe Effect Capacitive Sensors with Simultaneous High-Performance Contact and Non-Contact Sensing Capabilities SMALL STRUCTURES Ruth, S., Feig, V., Kim, M., Khan, Y., Phong, J., Bao, Z. 2021; 2 (2)

  View details for DOI 10.1002/sstr.202000079

  View details for Web of Science ID 000736592400010

• Achieving High Thermoelectric Performance and Metallic Transport in Solvent-Sheared PEDOT:PSS ADVANCED ELECTRONIC MATERIALS Hinckley, A. C., Andrews, S. C., Dunham, M. T., Sood, A., Barako, M. T., Schneider, S., Toney, M. F., Goodson, K. E., Bao, Z. 2021

  View details for DOI 10.1002/aelm.202001190

  View details for Web of Science ID 000612298700001

• Strain-insensitive intrinsically stretchable transistors and circuits NATURE ELECTRONICS Wang, W., Wang, S., Rastak, R., Ochiai, Y., Niu, S., Jiang, Y., Arunachala, P., Zheng, Y., Xu, J., Matsuhisa, N., Yan, X., Kwon, S., Miyakawa, M., Zhang, Z., Ning, R., Foudeh, A. M., Yun, Y., Linder, C., Tok, J., Bao, Z. 2021

  View details for DOI 10.1038/s41928-020-00525-1

  View details for Web of Science ID 000611472500001

• Polymers in Lithium-Ion and Lithium Metal Batteries ADVANCED ENERGY MATERIALS Li, J., Cai, Y., Wu, H., Yu, Z., Yan, X., Zhang, Q., Gao, T. Z., Liu, K., Jia, X., Bao, Z. 2021

  View details for DOI 10.1002/aenm.202003239

  View details for Web of Science ID 000611072100001

• Metal-Ligand Based Mechanophores Enhance Both Mechanical Robustness and Electronic Performance of Polymer Semiconductors ADVANCED FUNCTIONAL MATERIALS Wu, H., Lissel, F., Wang, G., Koshy, D. M., Nikzad, S., Yan, H., Xu, J., Luo, S., Matsuhisa, N., Cheng, Y., Wang, F., Ji, B., Li, D., Chen, W., Xue, G., Bao, Z. 2021

  View details for DOI 10.1002/adfm.202009201

  View details for Web of Science ID 000606958500001

• Monolithic optical microlithography of high-density elastic circuits. Science (New York, N.Y.) Zheng, Y. Q., Liu, Y., Zhong, D., Nikzad, S., Liu, S., Yu, Z., Liu, D., Wu, H. C., Zhu, C., Li, J., Tran, H., Tok, J. B., Bao, Z. 2021; 373 (6550): 88-94

  Abstract

  Polymeric electronic materials have enabled soft and stretchable electronics. However, the lack of a universal micro/nanofabrication method for skin-like and elastic circuits results in low device density and limited parallel signal recording and processing ability relative to silicon-based devices. We present a monolithic optical microlithographic process that directly micropatterns a set of elastic electronic materials by sequential ultraviolet light-triggered solubility modulation. We fabricated transistors with channel lengths of 2 micrometers at a density of 42,000 transistors per square centimeter. We fabricated elastic circuits including an XOR gate and a half adder, both of which are essential components for an arithmetic logic unit. Our process offers a route to realize wafer-level fabrication of complex, high-density, and multilayered elastic circuits with performance rivaling that of their rigid counterparts.

  View details for DOI 10.1126/science.abh3551

  View details for PubMedID 34210882

• Stress Markers for Mental States and Biotypes of Depression and Anxiety: A Scoping Review and Preliminary Illustrative Analysis. Chronic stress (Thousand Oaks, Calif.) Chesnut, M., Harati, S., Paredes, P., Khan, Y., Foudeh, A., Kim, J., Bao, Z., Williams, L. M. 2021; 5: 24705470211000338

  Abstract

  Depression and anxiety disrupt daily function and their effects can be long-lasting and devastating, yet there are no established physiological indicators that can be used to predict onset, diagnose, or target treatments. In this review, we conceptualize depression and anxiety as maladaptive responses to repetitive stress. We provide an overview of the role of chronic stress in depression and anxiety and a review of current knowledge on objective stress indicators of depression and anxiety. We focused on cortisol, heart rate variability and skin conductance that have been well studied in depression and anxiety and implicated in clinical emotional states. A targeted PubMed search was undertaken prioritizing meta-analyses that have linked depression and anxiety to cortisol, heart rate variability and skin conductance. Consistent findings include reduced heart rate variability across depression and anxiety, reduced tonic and phasic skin conductance in depression, and elevated cortisol at different times of day and across the day in depression. We then provide a brief overview of neural circuit disruptions that characterize particular types of depression and anxiety. We also include an illustrative analysis using predictive models to determine how stress markers contribute to specific subgroups of symptoms and how neural circuits add meaningfully to this prediction. For this, we implemented a tree-based multi-class classification model with physiological markers of heart rate variability as predictors and four symptom subtypes, including normative mood, as target variables. We achieved 40% accuracy on the validation set. We then added the neural circuit measures into our predictor set to identify the combination of neural circuit dysfunctions and physiological markers that accurately predict each symptom subtype. Achieving 54% accuracy suggested a strong relationship between those neural-physiological predictors and the mental states that characterize each subtype. Further work to elucidate the complex relationships between physiological markers, neural circuit dysfunction and resulting symptoms would advance our understanding of the pathophysiological pathways underlying depression and anxiety.

  View details for DOI 10.1177/24705470211000338

  View details for PubMedID 33997582

• Electrolyte-gated transistors for enhanced performance bioelectronics. Nature reviews. Methods primers Torricelli, F., Adrahtas, D. Z., Bao, Z., Berggren, M., Biscarini, F., Bonfiglio, A., Bortolotti, C. A., Frisbie, C. D., Macchia, E., Malliaras, G. G., McCulloch, I., Moser, M., Nguyen, T., Owens, R. M., Salleo, A., Spanu, A., Torsi, L. 2021; 1

  Abstract

  Electrolyte-gated transistors (EGTs), capable of transducing biological and biochemical inputs into amplified electronic signals and stably operating in aqueous environments, have emerged as fundamental building blocks in bioelectronics. In this Primer, the different EGT architectures are described with the fundamental mechanisms underpinning their functional operation, providing insight into key experiments including necessary data analysis and validation. Several organic and inorganic materials used in the EGT structures and the different fabrication approaches for an optimal experimental design are presented and compared. The functional bio-layers and/or biosystems integrated into or interfaced to EGTs, including self-organization and self-assembly strategies, are reviewed. Relevant and promising applications are discussed, including two-dimensional and three-dimensional cell monitoring, ultra-sensitive biosensors, electrophysiology, synaptic and neuromorphic bio-interfaces, prosthetics and robotics. Advantages, limitations and possible optimizations are also surveyed. Finally, current issues and future directions for further developments and applications are discussed.

  View details for DOI 10.1038/s43586-021-00065-8

  View details for PubMedID 35475166

• Tuning Conjugated Polymer Chain Packing for Stretchable Semiconductors. Advanced materials (Deerfield Beach, Fla.) Xu, J., Wu, H. C., Mun, J., Ning, R., Wang, W., Wang, G. N., Nikzad, S., Yan, H., Gu, X., Luo, S., Zhou, D., Tok, J. B., Bao, Z. 2021: e2104747

  Abstract

  In order to apply polymer semiconductors to stretchable electronics, they need to be easily deformed under strain without being damaged. A small number of conjugated polymers, typically with semicrystalline packing structures, have been reported to exhibit mechanical stretchability. Herein, a method is reported to modify polymer semiconductor packing-structure using a molecular additive, dioctyl phthalate (DOP), which is found to act as a molecular spacer, to be inserted between the amorphous chain networks and disrupt the crystalline packing. As a result, large-crystal growth is suppressed while short-range aggregations of conjugated polymers are promoted, which leads to an improved mechanical stretchability without affecting charge-carrier transport. Due to the reduced conjugated polymer intermolecular interactions, strain-induced chain alignment and crystallization are observed. By adding DOP to a well-known conjugated polymer, poly[2,5-bis(4-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione-(E)-1,2-di(2,2'-bithiophen-5-yl)ethene] (DPPTVT), stretchable transistors are obtained with anisotropic charge-carrier mobilities under strain, and stable current output under strain up to 100%.

  View details for DOI 10.1002/adma.202104747

  View details for PubMedID 34558121

• High-frequency and intrinsically stretchable polymer diodes. Nature Matsuhisa, N., Niu, S., O'Neill, S. J., Kang, J., Ochiai, Y., Katsumata, T., Wu, H., Ashizawa, M., Wang, G. N., Zhong, D., Wang, X., Gong, X., Ning, R., Gong, H., You, I., Zheng, Y., Zhang, Z., Tok, J. B., Chen, X., Bao, Z. 2021; 600 (7888): 246-252

  Abstract

  Skin-like intrinsically stretchable soft electronic devices are essential to realize next-generation remote and preventative medicine for advanced personal healthcare1-4. The recent development of intrinsically stretchable conductors and semiconductors has enabled highly mechanically robust and skin-conformable electronic circuits or optoelectronic devices2,5-10. However, their operating frequencies have been limited to less than 100hertz, which is much lower than that required for many applications. Here we report intrinsically stretchable diodes-based on stretchable organic and nanomaterials-capable of operating at a frequency as high as 13.56megahertz. This operating frequency is high enough for the wireless operation of soft sensors and electrochromicdisplaypixels using radiofrequency identification in which the base-carrier frequency is 6.78megahertz or13.56megahertz. This was achieved through a combination of rational material design and device engineering. Specifically, we developed a stretchable anode, cathode, semiconductor and current collector that can satisfy the strict requirements for high-frequency operation. Finally, we show the operational feasibility of our diode by integrating it with a stretchable sensor, electrochromicdisplay pixel and antenna to realize a stretchable wireless tag. This work is an important step towards enabling enhanced functionalities and capabilities for skin-like wearable electronics.

  View details for DOI 10.1038/s41586-021-04053-6

  View details for PubMedID 34880427

• Designing Tunable Capacitive Pressure Sensors Based on Material Properties and Microstructure Geometry. ACS applied materials & interfaces Ruth, S. R., Bao, Z. 2020

  Abstract

  Rationally designed pressure sensors for target applications have been in increasing demand. Capacitive pressure sensors with microstructured dielectrics demonstrate a high capability of meeting this demand due to their wide versatility and high tunability by manipulating dielectric layer material and microstructure geometry. However, to streamline the design and fabrication of desirable sensors, a better understanding of how material microstructure and properties of the dielectric layer affect performance is vital. The ability to predict trends in sensor design and performance simplifies the process of designing and fabricating sensors for various applications. A series of equations are presented that can be used to predict trends in initial capacitance, capacitance change, and sensitivity based on dielectric constant and compressive modulus of the dielectric material and base length, interstructural separation, and height of the dielectric layer microstructures. The efficacy of this model has been experimentally and computationally confirmed. The model was then used to illuminate, qualitatively and quantitatively, the relationships between these key material properties and microstructure geometries. Finally, this model demonstrates high tunability and simple implementation for predictive sensor performance for a wide range of designs to help meet the growing demand for highly specialized sensors.

  View details for DOI 10.1021/acsami.0c19196

  View details for PubMedID 33345539

• A Cation-Tethered Flowable Polymeric Interface for Enabling Stable Deposition of Metallic Lithium. Journal of the American Chemical Society Huang, Z., Choudhury, S., Gong, H., Cui, Y., Bao, Z. 2020

  Abstract

  A fundamental challenge, shared across many energy storage devices, is the complexity of electrochemistry at the electrode-electrolyte interfaces that impacts the Coulombic efficiency, operational rate capability, and lifetime. Specifically, in energy-dense lithium metal batteries, the charging/discharging process results in structural heterogeneities of the metal anode, leading to battery failure by short-circuit and capacity fade. In this work, we take advantage of organic cations with lower reduction potential than lithium to build an electrically responsive polymer interface that not only adapts to morphological perturbations during electrodeposition and stripping but also modulates the lithium ion migration pathways to eliminate surface roughening. We find that this concept can enable prolonging the long-term cycling of a high-voltage lithium metal battery by at least twofold compared to bare lithium metal.

  View details for DOI 10.1021/jacs.0c09649

  View details for PubMedID 33314926

• Valence-Dependent Electrical Conductivity in a 3D Tetrahydroxyquinone-Based Metal-Organic Framework. Journal of the American Chemical Society Chen, G., Gee, L. B., Xu, W., Zhu, Y., Lezama-Pacheco, J. S., Huang, Z., Li, Z., Babicz, J. T., Choudhury, S., Chang, T., Reed, E., Solomon, E. I., Bao, Z. 2020

  Abstract

  Electrically conductive metal-organic frameworks (cMOFs) have become a topic of intense interest in recent years because of their great potential in electrochemical energy storage, electrocatalysis, and sensing applications. Most of the cMOFs reported hitherto are 2D structures, and 3D cMOFs remain rare. Herein we report FeTHQ, a 3D cMOF synthesized from tetrahydroxy-1,4-quinone (THQ) and iron(II) sulfate salt. FeTHQ exhibited a conductivity of 3.3 ± 0.55 mS cm-1 at 300 K, which is high for 3D cMOFs. The conductivity of FeTHQ is valence-dependent. A higher conductivity was measured with the as-prepared FeTHQ than with the air-oxidized and sodium naphthalenide-reduced samples.

  View details for DOI 10.1021/jacs.0c09379

  View details for PubMedID 33315385

• High Thermopower in a Zn-Based 3D Semiconductive Metal-Organic Framework. Journal of the American Chemical Society Park, J., Hinckley, A. C., Huang, Z., Chen, G., Yakovenko, A. A., Zou, X., Bao, Z. 2020

  Abstract

  Conductive metal-organic frameworks (c-MOFs) have drawn increasing attention for their outstanding performance in energy-related applications. However, the majority of reported c-MOFs are based on 2D structures. Synthetic strategies for 3D c-MOFs are under-explored, leaving unrealized functionality in both their structures and properties. Herein we report Zn-HAB, a 3D c-MOF comprised of hexaaminobenzene and Zn(II). Zn-HAB is shown to have microporosity with a band gap of approximately 1.68 eV, resulting in a moderate conductivity of 0.86 mS cm-1 and a high Seebeck coefficient of 200 muV K-1 at 300 K. The power factor of 3.44 nW m-1 K-2 constitutes the first report of the thermoelectric properties of an intrinsically conductive 3D MOF.

  View details for DOI 10.1021/jacs.0c09573

  View details for PubMedID 33226798

• Understanding the Mechanism of High Capacitance in Nickel Hexaaminobenzene-Based Conductive Metal-Organic Frameworks in Aqueous Electrolytes. ACS nano Lukatskaya, M. R., Feng, D., Bak, S., To, J. W., Yang, X., Cui, Y., Feldblyum, J. I., Bao, Z. 2020

  Abstract

  Recently, intrinsically conductive metal-organic frameworks (MOFs) have demonstrated promising performance in fast-charging energy storage applications and may outperform some current electrode materials (e.g., porous carbons) for supercapacitors in terms of both gravimetric and volumetric capacitance. In this report, we examine the mechanism of high capacitance in a nickel hexaaminobenzene-based MOF (NiHAB). Using a combination of in situ Raman and X-ray absorption spectroscopies, as well as detailed electrochemical studies in a series of aqueous electrolytes, we demonstrate that the charge storage mechanism is, in fact, a pH-dependent surface pseudocapacitance, and unlike typical inorganic systems, where transition metals change oxidation state during charge/discharge cycles, NiHAB redox activity is ligand-centered.

  View details for DOI 10.1021/acsnano.0c07292

  View details for PubMedID 33166110

• A Low-Temperature Boost for Stretchable Conductors MATTER Feig, V., Bao, Z. 2020; 3 (4): 983–84

  View details for DOI 10.1016/j.matt.2020.09.010

  View details for Web of Science ID 000581132600007

• Topological origin of strain induced damage of multi-network elastomers by bond breaking EXTREME MECHANICS LETTERS Yin, Y., Bertin, N., Wang, Y., Bao, Z., Cai, W. 2020; 40

  View details for DOI 10.1016/j.eml.2020.100883

  View details for Web of Science ID 000577470700016

• Tuning the Self-Healing Response of Poly(dimethylsiloxane)-Based Elastomers ACS APPLIED POLYMER MATERIALS Doehler, D., Kang, J., Cooper, C., Tok, J., Rupp, H., Binder, W. H., Bao, Z. 2020; 2 (9): 4127–39

  View details for DOI 10.1021/acsapm.0c00755

  View details for Web of Science ID 000571515200044

• Direct Characterization of Atomically Dispersed Catalysts: Nitrogen-Coordinated Ni Sites in Carbon-Based Materials for CO(2)Electroreduction ADVANCED ENERGY MATERIALS Koshy, D. M., Landers, A. T., Cullen, D. A., Ievlev, A., Meyer, H. M., Hahn, C., Bao, Z., Jaramillo, T. F. 2020

  View details for DOI 10.1002/aenm.202001836

  View details for Web of Science ID 000565386000001

• Dense Carbon Nanoflower Pellets for Methane Storage ACS APPLIED NANO MATERIALS Chen, S., Gong, H., Dindoruk, B., He, J., Bao, Z. 2020; 3 (8): 8278–85

  View details for DOI 10.1021/acsanm.0c01700

  View details for Web of Science ID 000566778600103

• Nanosized Zirconium Porphyrinic Metal-Organic Frameworks that Catalyze the Oxygen Reduction Reaction in Acid SMALL METHODS Chen, G., Stevens, M., Liu, Y., King, L. A., Park, J., Kim, T., Sinclair, R., Jaramillo, T. F., Bao, Z. 2020

  View details for DOI 10.1002/smtd.202000085

  View details for Web of Science ID 000557369400001

• Microengineering Pressure Sensor Active Layers for Improved Performance ADVANCED FUNCTIONAL MATERIALS Ruth, S., Feig, V., Tran, H., Bao, Z. 2020

  View details for DOI 10.1002/adfm.202003491

  View details for Web of Science ID 000557386000001

• A Carbon Flower Based Flexible Pressure Sensor Made from Large-Area Coating ADVANCED MATERIALS INTERFACES O'Neill, S. K., Gong, H., Matsuhisa, N., Chen, S., Moon, H., Wu, H., Chen, X., Chen, X., Bao, Z. 2020

  View details for DOI 10.1002/admi.202000875

  View details for Web of Science ID 000553780500001

• Effects of Water and Different Solutes on Carbon-Nanotube Low-Voltage Field-Effect Transistors. Small (Weinheim an der Bergstrasse, Germany) Foudeh, A. M., Pfattner, R., Lu, S., Kubzdela, N. S., Gao, T. Z., Lei, T., Bao, Z. 2020: e2002875

  Abstract

  Semiconducting single-walled carbon nanotubes (swCNTs) are a promising class of materials for emerging applications. In particular, they are demonstrated to possess excellent biosensing capabilities, and are poised to address existing challenges in sensor reliability, sensitivity, and selectivity. This work focuses on swCNT field-effect transistors (FETs) employing rubbery double-layer capacitive dielectric poly(vinylidene fluoride-co-hexafluoropropylene). These devices exhibit small device-to-device variation as well as high current output at low voltages (<0.5 V), making them compatible with most physiological liquids. Using this platform, the swCNT devices are directly exposed to aqueous solutions containing different solutes to characterize their effects on FET current-voltage (FET I-V) characteristics. Clear deviation from ideal characteristics is observed when swCNTs are directly contacted by water. Such changes are attributed to strong interactions between water molecules and sp2 -hybridized carbon structures. Selective response to Hg2+ is discussed along with reversible pH effect using two distinct device geometries. Additionally, the influence of aqueous ammonium/ammonia in direct contact with the swCNTs is investigated. Understanding the FET I-V characteristics of low-voltage swCNT FETs may provide insights for future development of stable, reliable, and selective biosensor systems.

  View details for DOI 10.1002/smll.202002875

  View details for PubMedID 32691979

• Tuning the Mechanical Properties of a Polymer Semiconductor by Modulating Hydrogen Bonding Interactions CHEMISTRY OF MATERIALS Zheng, Y., Ashizawa, M., Zhang, S., Kang, J., Nikzad, S., Yu, Z., Ochiai, Y., Wu, H., Tran, H., Mun, J., Zheng, Y., Tok, J., Gu, X., Bao, Z. 2020; 32 (13): 5700–5714

  View details for DOI 10.1021/acs.chemmater.0c01437

  View details for Web of Science ID 000551412800030

• Fully stretchable active-matrix organic light-emitting electrochemical cell array. Nature communications Liu, J., Wang, J., Zhang, Z., Molina-Lopez, F., Wang, G. N., Schroeder, B. C., Yan, X., Zeng, Y., Zhao, O., Tran, H., Lei, T., Lu, Y., Wang, Y., Tok, J. B., Dauskardt, R., Chung, J. W., Yun, Y., Bao, Z. 2020; 11 (1): 3362

  Abstract

  Intrinsically and fully stretchable active-matrix-driven displays are an important element to skin electronics that can be applied to many emerging fields, such as wearable electronics, consumer electronics and biomedical devices. Here, we show for the first time a fully stretchable active-matrix-driven organic light-emitting electrochemical cell array. Briefly, it is comprised of a stretchable light-emitting electrochemical cell array driven by a solution-processed, vertically integrated stretchable organic thin-film transistor active-matrix, which is enabled by the development of chemically-orthogonal and intrinsically stretchable dielectric materials. Our resulting active-matrix-driven organic light-emitting electrochemical cell array can be readily bent, twisted and stretched without affecting its device performance. When mounted on skin, the array can tolerate to repeated cycles at 30% strain. This work demonstrates the feasibility of skin-applicable displays and lays the foundation for further materials development.

  View details for DOI 10.1038/s41467-020-17084-w

  View details for PubMedID 32620794

• Flexible smart bandage for wireless wound healing Trotsyuk, A. A., Jiang, Y., Niu, S., Larson, M., Beard, E., Saberi, A., Henn, D., Kwon, S., Bonham, C., Chen, K., Januszyk, M., Maan, Z., Barrera, J., Padmanabhan, J., Fischer, K. S., Bao, Z., Gurtner, G. C. WILEY. 2020: S24

  View details for Web of Science ID 000548418300050

• Rational Design of Capacitive Pressure Sensors Based on Pyramidal Microstructures for Specialized Monitoring of Biosignals ADVANCED FUNCTIONAL MATERIALS Ruth, S., Beker, L., Tran, H., Feig, V., Matsuhisa, N., Bao, Z. 2020; 30 (29)

  View details for DOI 10.1002/adfm.201903100

  View details for Web of Science ID 000553158100009

• A Compact Free-Floating Device for Passive Charge-Balanced Neural Stimulation using PEDOT/CNT microelectrodes. Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference Khalifa, A., Liu, Y., Bao, Z., Etienne-Cummings, R. 2020; 2020: 3375–78

  Abstract

  Wirelessly powered implants are increasingly being developed as free-floating single-channel devices to interface with neurons directly at stimulation sites. In order to stimulate neurons in a manner that is safe to both the electrode and the surrounding tissue, charge accumulation over time needs to be avoided. The implementation of conventional charge balancing methods often leads to an increase in system complexity, power consumption or area, all of which are critical parameters in ultra-small wireless devices. The proposed charge balancing method described in this work, which relies on bipolar capacitive integrated electrodes, does not increase these parameters. The standalone wirelessly powered stimulating implant is implemented in a 130nm CMOS technology and measures 0.009 mm3.

  View details for DOI 10.1109/EMBC44109.2020.9176643

  View details for PubMedID 33018728

• Enabling Deformable and Stretchable Batteries ADVANCED ENERGY MATERIALS Mackanic, D. G., Kao, M., Bao, Z. 2020

  View details for DOI 10.1002/aenm.202001424

  View details for Web of Science ID 000542184900001

• Molecular design for electrolyte solvents enabling energy-dense and long-cycling lithium metal batteries NATURE ENERGY Yu, Z., Wang, H., Kong, X., Huang, W., Tsao, Y., Mackanic, D. G., Wang, K., Wang, X., Huang, W., Choudhury, S., Zheng, Y., Amanchukwu, C., Hung, S. T., Ma, Y., Lomeli, E. G., Qin, J., Cui, Y., Bao, Z. 2020

  View details for DOI 10.1038/s41560-020-0634-5

  View details for Web of Science ID 000542060100001

• Engineering Supramolecular Polymer Conformation for Efficient Carbon Nanotube Sorting. Small (Weinheim an der Bergstrasse, Germany) Gao, T. Z., Sun, Z., Yan, X., Wu, H., Yan, H., Bao, Z. 2020: e2000923

  Abstract

  Supramolecular polymer sorting is a promising approach to separating single-walled carbon nanotubes (CNTs) by electronic type. Unlike conjugated polymers, they can be easily removed from the CNTs after sorting by breaking the supramolecular bonds, allowing for isolation of electronically pristine CNTs as well as facile recycling of the sorting polymer. However, little is understood about how supramolecular polymer properties affect CNT sorting. Herein, chain stoppers are used to engineer the conformation of a supramolecular sorting polymer, thereby elucidating the relationship between sorting efficacy and polymer conformation. Through NMR and UV-vis spectroscopy, small-angle X-ray scattering (SAXS), and thermodynamic modeling, it is shown that this supramolecular polymer exhibits ring-chain equilibrium, and that this equilibrium can be skewed toward chains by the addition of chain stoppers. Furthermore, by controlling the stopper-monomer ratio, the sorting yield can be doubled from 7% to 14% without compromising the semiconducting purity (>99%) or properties of sorted CNTs.

  View details for DOI 10.1002/smll.202000923

  View details for PubMedID 32500637

• Stretchable electrochemical energy storage devices. Chemical Society reviews Mackanic, D. G., Chang, T., Huang, Z., Cui, Y., Bao, Z. 2020

  Abstract

  The increasingly intimate contact between electronics and the human body necessitates the development of stretchable energy storage devices that can conform and adapt to the skin. As such, the development of stretchable batteries and supercapacitors has received significant attention in recent years. This review provides an overview of the general operating principles of batteries and supercapacitors and the requirements to make these devices stretchable. The following sections provide an in-depth analysis of different strategies to convert the conventionally rigid electrochemical energy storage materials into stretchable form factors. Namely, the strategies of strain engineering, rigid island geometry, fiber-like geometry, and intrinsic stretchability are discussed. A wide range of materials are covered for each strategy, including polymers, metals, and ceramics. By comparing the achieved electrochemical performance and strain capability of these different materials strategies, we allow for a side-by-side comparison of the most promising strategies for enabling stretchable electrochemical energy storage. The final section consists of an outlook for future developments and challenges for stretchable supercapacitors and batteries.

  View details for DOI 10.1039/d0cs00035c

  View details for PubMedID 32483575

• F4-TCNQ as an Additive to Impart Stretchable Semiconductors with High Mobility and Stability ADVANCED ELECTRONIC MATERIALS Mun, J., Kang, J., Zheng, Y., Luo, S., Wu, Y., Gong, H., Lai, J., Wu, H., Xue, G., Tok, J., Bao, Z. 2020

  View details for DOI 10.1002/aelm.202000251

  View details for Web of Science ID 000533295700001

• A bioinspired stretchable membrane-based compliance sensor. Proceedings of the National Academy of Sciences of the United States of America Beker, L., Matsuhisa, N., You, I., Ruth, S. R., Niu, S., Foudeh, A., Tok, J. B., Chen, X., Bao, Z. 2020

  Abstract

  Compliance sensation is a unique feature of the human skin that electronic devices could not mimic via compact and thin form-factor devices. Due to the complex nature of the sensing mechanism, up to now, only high-precision or bulky handheld devices have been used to measure compliance of materials. This also prevents the development of electronic skin that is fully capable of mimicking human skin. Here, we developed a thin sensor that consists of a strain sensor coupled to a pressure sensor and is capable of identifying compliance of touched materials. The sensor can be easily integrated into robotic systems due to its small form factor. Results showed that the sensor is capable of classifying compliance of materials with high sensitivity allowing materials with various compliance to be identified. We integrated the sensor to a robotic finger to demonstrate the capability of the sensor for robotics. Further, the arrayed sensor configuration allows a compliance mapping which can enable humanlike sensations to robotic systems when grasping objects composed of multiple materials of varying compliance. These highly tunable sensors enable robotic systems to handle more advanced and complicated tasks such as classifying touched materials.

  View details for DOI 10.1073/pnas.1909532117

  View details for PubMedID 32385155

• Electronic skins and machine learning for intelligent soft robots SCIENCE ROBOTICS Shih, B., Shah, D., Li, J., Thuruthel, T. G., Park, Y., Iida, F., Bao, Z., Kramer-Bottiglio, R., Tolley, M. T. 2020; 5 (41)

  View details for DOI 10.1126/scirobotics.aaz9239

  View details for Web of Science ID 000550012800001

• Electronic skins and machine learning for intelligent soft robots. Science robotics Shih, B., Shah, D., Li, J., Thuruthel, T. G., Park, Y. L., Iida, F., Bao, Z., Kramer-Bottiglio, R., Tolley, M. T. 2020; 5 (41)

  Abstract

  Soft robots have garnered interest for real-world applications because of their intrinsic safety embedded at the material level. These robots use deformable materials capable of shape and behavioral changes and allow conformable physical contact for manipulation. Yet, with the introduction of soft and stretchable materials to robotic systems comes a myriad of challenges for sensor integration, including multimodal sensing capable of stretching, embedment of high-resolution but large-area sensor arrays, and sensor fusion with an increasing volume of data. This Review explores the emerging confluence of e-skins and machine learning, with a focus on how roboticists can combine recent developments from the two fields to build autonomous, deployable soft robots, integrated with capabilities for informative touch and proprioception to stand up to the challenges of real-world environments.

  View details for DOI 10.1126/scirobotics.aaz9239

  View details for PubMedID 33022628

• A New Class of Ionically Conducting Fluorinated Ether Electrolytes with High Electrochemical Stability. Journal of the American Chemical Society Amanchukwu, C. V., Yu, Z., Kong, X., Qin, J., Cui, Y., Bao, Z. 2020

  Abstract

  Increasing battery energy density is greatly desired for applications such as portable electronics and transportation. However, many next-generation batteries are limited by electrolyte selection because high ionic conductivity and poor electrochemical stability are typically observed in most electrolytes. For example, ether-based electrolytes have high ionic conductivity but are oxidatively unstable above 4 V, which prevents the use of high-voltage cathodes that promise higher energy densities. In contrast, hydrofluoroethers (HFEs) have high oxidative stability but do not dissolve lithium salt. In this work, we synthesize a new class of fluorinated ether electrolytes that combine the oxidative stability of HFEs with the ionic conductivity of ethers in a single compound. We show that conductivities of up to 2.7 * 10-4 S/cm (at 30 °C) can be obtained with oxidative stability up to 5.6 V. The compounds also show higher lithium transference numbers compared to typical ethers. Furthermore, we use nuclear magnetic resonance (NMR) and molecular dynamics (MD) to study their ionic transport behavior and ion solvation environment, respectively. Finally, we demonstrate that this new class of electrolytes can be used with a Ni-rich layered cathode (NMC 811) to obtain over 100 cycles at a C/5 rate. The design of new molecules with high ionic conductivity and high electrochemical stability is a novel approach for the rational design of next-generation batteries.

  View details for DOI 10.1021/jacs.9b11056

  View details for PubMedID 32233433

• Skin-inspired electronics: emerging semiconductor devices and systems JOURNAL OF SEMICONDUCTORS Ma, Z., Kong, D., Pan, L., Bao, Z. 2020; 41 (4)

  View details for DOI 10.1088/1674-4926/41/4/041601

  View details for Web of Science ID 000536904100001

• Wireless smart contact lens for diabetic diagnosis and therapy SCIENCE ADVANCES Keum, D., Kim, S., Koo, J., Lee, G., Jeon, C., Mok, J., Mun, B., Lee, K., Kamrani, E., Joo, C., Shin, S., Sim, J., Myung, D., Yun, S., Bao, Z., Hahn, S. 2020; 6 (17): eaba3252

  Abstract

  A smart contact lens can be used as an excellent interface between the human body and an electronic device for wearable healthcare applications. Despite wide investigations of smart contact lenses for diagnostic applications, there has been no report on electrically controlled drug delivery in combination with real-time biometric analysis. Here, we developed smart contact lenses for both continuous glucose monitoring and treatment of diabetic retinopathy. The smart contact lens device, built on a biocompatible polymer, contains ultrathin, flexible electrical circuits and a microcontroller chip for real-time electrochemical biosensing, on-demand controlled drug delivery, wireless power management, and data communication. In diabetic rabbit models, we could measure tear glucose levels to be validated by the conventional invasive blood glucose tests and trigger drugs to be released from reservoirs for treating diabetic retinopathy. Together, we successfully demonstrated the feasibility of smart contact lenses for noninvasive and continuous diabetic diagnosis and diabetic retinopathy therapy.

  View details for DOI 10.1126/sciadv.aba3252

  View details for Web of Science ID 000530628100044

  View details for PubMedID 32426469

  View details for PubMedCentralID PMC7182412

• Process design kit and design automation for flexible hybrid electronics JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY Huang, T., Lei, T., Shao, L., Sivapurapu, S., Swaminathan, M., Bao, Z., Cheng, K., Beausoleil, R. 2020

  View details for DOI 10.1002/jsid.876

  View details for Web of Science ID 000513693800001

• Dendrite Suppression by a Polymer Coating: A Coarse-Grained Molecular Study ADVANCED FUNCTIONAL MATERIALS Kong, X., Rudnicki, P. E., Choudhury, S., Bao, Z., Qin, J. 2020

  View details for DOI 10.1002/adfm.201910138

  View details for Web of Science ID 000513653700001

• Multifunctional materials for implantable and wearable photonic healthcare devices. Nature reviews. Materials Lee, G. H., Moon, H., Kim, H., Lee, G. H., Kwon, W., Yoo, S., Myung, D., Yun, S. H., Bao, Z., Hahn, S. K. 2020; 5 (2): 149-165

  Abstract

  Numerous light-based diagnostic and therapeutic devices are routinely used in the clinic. These devices have a familiar look as items plugged in the wall or placed at patients' bedsides, but recently, many new ideas have been proposed for the realization of implantable or wearable functional devices. Many advances are being fuelled by the development of multifunctional materials for photonic healthcare devices. However, the finite depth of light penetration in the body is still a serious constraint for their clinical applications. In this Review, we discuss the basic concepts and some examples of state-of-the-art implantable and wearable photonic healthcare devices for diagnostic and therapeutic applications. First, we describe emerging multifunctional materials critical to the advent of next-generation implantable and wearable photonic healthcare devices and discuss the path for their clinical translation. Then, we examine implantable photonic healthcare devices in terms of their properties and diagnostic and therapeutic functions. We next describe exemplary cases of noninvasive, wearable photonic healthcare devices across different anatomical applications. Finally, we discuss the future research directions for the field, in particular regarding mobile healthcare and personalized medicine.

  View details for DOI 10.1038/s41578-019-0167-3

  View details for PubMedID 32728478

  View details for PubMedCentralID PMC7388681

• Biodegradable and stretchable polymeric materials for transient electronic devices MRS BULLETIN Liu, K., Tran, H., Feig, V., Bao, Z. 2020; 45 (2): 96–102

  View details for DOI 10.1557/mrs.2020.24

  View details for Web of Science ID 000578280100008

• Inducing Molecular Aggregation of Polymer Semiconductors in a Secondary Insulating Polymer Matrix to Enhance Charge Transport CHEMISTRY OF MATERIALS Nikzad, S., Wu, H., Kim, J., Mahoney, C. M., Matthews, J. R., Niu, W., Li, Y., Wang, H., Chen, W., Toney, M. F., He, M., Bao, Z. 2020; 32 (2): 897–905

  View details for DOI 10.1021/acs.chemmater.9b05228

  View details for Web of Science ID 000510530500028

• Multifunctional materials for implantable and wearable photonic healthcare devices NATURE REVIEWS MATERIALS Lee, G., Moon, H., Kim, H., Lee, G., Kwon, W., Yoo, S., Myung, D., Yun, S., Bao, Z., Hahn, S. 2020

  View details for DOI 10.1038/s41578-019-0167-3

  View details for Web of Science ID 000508153800001

• Ink Development and Printing of Conducting Polymers for Intrinsically Stretchable Interconnects and Circuits ADVANCED ELECTRONIC MATERIALS Kraft, U., Molina-Lopez, F., Son, D., Bao, Z., Murmann, B. 2020; 6 (1)

  View details for DOI 10.1002/aelm.201900681

  View details for Web of Science ID 000507306800041

• Design Principles of Artificial Solid Electrolyte Interphases for Lithium-Metal Anodes Cell Reports Physical Science Yu, Z., Cui, Y., Bao, Z. 2020; 1 (7): 100119

  View details for DOI 10.1016/j.xcrp.2020.100119

• Wearable System Design Using Intrinsically Stretchable Temperature Sensor Zhu, C., Schell, E., Kim, M., Bao, Z., Murmann, B., IEEE IEEE. 2020

  View details for Web of Science ID 000696570700112

• Robust Design of Large Area Flexible Electronics via Compressed Sensing Shao, L., Lei, T., Huang, T., Bao, Z., Cheng, K., IEEE IEEE. 2020

  View details for Web of Science ID 000628528400078

• A Compact Free-Floating Device for Passive Charge-Balanced Neural Stimulation using PEDOT/CNT microelectrodes Khalifa, A., Liu, Y., Bao, Z., Etienne-Cummings, R., IEEE IEEE. 2020: 3375–78

  View details for Web of Science ID 000621592203177

• Morphing electronics enable neuromodulation in growing tissue. Nature biotechnology Liu, Y. n., Li, J. n., Song, S. n., Kang, J. n., Tsao, Y. n., Chen, S. n., Mottni, V. n., McConnell, K. n., Xu, W. n., Zheng, Y. Q., Tok, J. B., George, P. M., Bao, Z. n. 2020

  Abstract

  Bioelectronics for modulating the nervous system have shown promise in treating neurological diseases1-3. However, their fixed dimensions cannot accommodate rapid tissue growth4,5 and may impair development6. For infants, children and adolescents, once implanted devices are outgrown, additional surgeries are often needed for device replacement, leading to repeated interventions and complications6-8. Here, we address this limitation with morphing electronics, which adapt to in vivo nerve tissue growth with minimal mechanical constraint. We design and fabricate multilayered morphing electronics, consisting of viscoplastic electrodes and a strain sensor that eliminate the stress at the interface between the electronics and growing tissue. The ability of morphing electronics to self-heal during implantation surgery allows a reconfigurable and seamless neural interface. During the fastest growth period in rats, morphing electronics caused minimal damage to the rat nerve, which grows 2.4-fold in diameter, and allowed chronic electrical stimulation and monitoring for 2 months without disruption of functional behavior. Morphing electronics offers a path toward growth-adaptive pediatric electronic medicine.

  View details for DOI 10.1038/s41587-020-0495-2

  View details for PubMedID 32313193

• Two-Dimensional Conductive Ni-HAB as a Catalyst for the Electrochemical Oxygen Reduction Reaction. ACS applied materials & interfaces Park, J. n., Chen, Z. n., Flores, R. A., Wallnerström, G. n., Kulkarni, A. n., Nørskov, J. K., Jaramillo, T. F., Bao, Z. n. 2020

  Abstract

  Catalytic systems whose properties can be systematically tuned via changes in synthesis conditions are highly desirable for the next-generation catalyst design and optimization. Herein, we present a two-dimensional (2D) conductive metal-organic framework consisting of M-N4 units (M = Ni, Cu) and a hexaaminobenzene (HAB) linker as a catalyst for the oxygen reduction reaction. By varying synthetic conditions, we prepared two Ni-HAB catalysts with different crystallinities, resulting in catalytic systems with different electric conductivities, electrochemical activity, and stability. We show that crystallinity has a positive impact on conductivity and demonstrate that this improved crystallinity/conductivity improves the catalytic performance of our model system. Additionally, density functional theory simulations were performed to probe the origin of M-HAB's catalytic activity, and they suggest that M-HAB's organic linker acts as the active site with the role of the metal being to modulate the linker sites' binding strength.

  View details for DOI 10.1021/acsami.0c09323

  View details for PubMedID 32805928

• Intrinsically stretchable conjugated polymer semiconductors in field effect transistors PROGRESS IN POLYMER SCIENCE Ashizawa, M., Zheng, Y., Tran, H., Bao, Z. 2020; 100

  View details for DOI 10.1016/j.progpolymsci.2019.101181

  View details for Web of Science ID 000504743100002

• Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni, N-doped Carbon Catalysts. Angewandte Chemie (International ed. in English) Koshy, D. n., Chen, S. n., Lee, D. U., Burke Stevens, M. n., Abdellah, A. n., Dull, S. n., Chen, G. n., Nordlund, D. n., Gallo, A. n., Hahn, C. n., Higgins, D. C., Bao, Z. n., Jaramillo, T. n. 2020

  Abstract

  Ni,N-doped carbon catalysts have shown promising catalytic performance for CO 2 electroreduction (CO 2 R) to CO; this activity has been attributed to the presence of nitrogen-coordinated, single metal atom active sites. However, experimentally confirming Ni-N bonding and correlating CO 2 reduction (CO 2 R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni, N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO- 2 R to CO partial current density increased with increased Ni content before plateauing at 2 wt% which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft x-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal-porphyrin catalysts.

  View details for DOI 10.1002/anie.201912857

  View details for PubMedID 31919948

• Author Correction: Morphing electronics enable neuromodulation in growing tissue. Nature biotechnology Liu, Y. n., Li, J. n., Song, S. n., Kang, J. n., Tsao, Y. n., Chen, S. n., Mottini, V. n., McConnell, K. n., Xu, W. n., Zheng, Y. Q., Tok, J. B., George, P. M., Bao, Z. n. 2020

  Abstract

  An amendment to this paper has been published and can be accessed via a link at the top of the paper.

  View details for DOI 10.1038/s41587-020-0533-0

  View details for PubMedID 32341566

• Transient Voltammetry with Ultramicroelectrodes Reveals the Electron Transfer Kinetics of Lithium Metal Anodes Adv. Energy Lett. Boyle, D., Kong, X., Pei, A., Rudnicki, P., Shi, F., Huang, W., Bao, Z., Qin, J., Cui, Y. 2020; 5: 701-709

  View details for DOI 10.1021/acsenergylett.0c00031

• Multivalent Assembly of Flexible Polymer Chains into Supramolecular Nanofibers. Journal of the American Chemical Society Cooper, C. B., Kang, J. n., Yin, Y. n., Yu, Z. n., Wu, H. C., Nikzad, S. n., Ochiai, Y. n., Yan, H. n., Cai, W. n., Bao, Z. n. 2020

  Abstract

  Polymeric materials in nature regularly employ ordered, hierarchical structures in order to perform unique and precise functions. Importantly, these structures are often formed and stabilized by the cooperative summation of many weak interactions as opposed to the independent association of a few strong bonds. Here, we show that synthetic, flexible polymer chains with periodically placed and directional dynamic bonds collectively assemble into supramolecular nanofibers when the overall molecular weight is below the polymer's critical entanglement molecular weight. This causes bulk films of long polymer chains to have faster dynamics than films of shorter polymer chains of identical chemical composition. The formation of nanofibers increases the bulk film modulus by over an order of magnitude and delays the onset of terminal flow by more than 100 °C, while still remaining solution processable. Systematic investigation of different polymer chain architectures and dynamic bonding moieties along with coarse-grained molecular dynamics simulations illuminate governing structure-function relationships that determine a polymer's capacity to form supramolecular nanofibers. This report of the cooperative assembly of multivalent polymer chains into hierarchical, supramolecular structures contributes to our fundamental understanding of designing biomimetic functional materials.

  View details for DOI 10.1021/jacs.0c07651

  View details for PubMedID 32901473

• Low-Voltage, Dual-Gate Organic Transistors with High Sensitivity and Stability toward Electrostatic Biosensing. ACS applied materials & interfaces Nikolka, M. n., Simatos, D. n., Foudeh, A. n., Pfattner, R. n., McCulloch, I. n., Bao, Z. n. 2020; 12 (36): 40581–89

  Abstract

  High levels of performance and stability have been demonstrated for conjugated polymer thin-film transistors in recent years, making them promising materials for flexible electronic circuits and displays. For sensing applications, however, most research efforts have been focusing on electrochemical sensing devices. Here we demonstrate a highly stable biosensing platform using polymer transistors based on the dual-gate mechanism. In this architecture a sensing signal is transduced and amplified by the capacitive coupling between a low-k bottom dielectric and a high-k ionic elastomer top dielectric that is in contact with an analyte solution. The new design exhibits a high signal amplification, high stability under bias stress in various aqueous environments, and low signal drift. Our platform, furthermore, while responding expectedly to charged analytes such as the protein bovine serum albumin, is insensitive to changes of salt concentration of the analyte solution. These features make this platform a potentially suitable tool for a variety of biosensing applications.

  View details for DOI 10.1021/acsami.0c10201

  View details for PubMedID 32805944

• Air-Stability and Carrier Type in Conductive M3(Hexaaminobenzene)2, (M = Co, Ni, Cu). Journal of the American Chemical Society Hinckley, A. C., Park, J. n., Gomes, J. n., Carlson, E. n., Bao, Z. n. 2020

  Abstract

  Herein, we investigate the effects of changing the metal ions in the M-HAB system, with HAB = hexaaminobenzene ligands and M = Co, Ni, Cu. The phyiscal characteristics of this MOF family are insensitive to changes in the metal cation, which enables systematic evaluation of the effect of metal cation identity on electrical transport properties. We observe that the metal ion profoundly influences the electrical conductivity and dominant carrier type in the resulting MOF and the air-stability thereof. Cu-HAB and Co-HAB are determined to exhibit n-type conduction under both ambient and nitrogen conditions; Ni-HAB is found to be ambipolar, with its dominant carrier type dramatically affected by the environment. We examine these results through calculation of the band structure, the partial density of states, and charge transfer analysis. Unlike traditional conductive organic materials, we find that the air-stability is not well predicted by the LUMO level of these n-type MOFs but instead is additionally dependent on the occupancy and orientation of the metal ion's d-orbitals and the resulting interaction between the metal ion and ligand. This study provides fundamental insights for rational design of air-stable, electronically conductive MOFs.

  View details for DOI 10.1021/jacs.0c03500

  View details for PubMedID 32475120

• Biomimetic Impact Protective Supramolecular Polymeric Materials Enabled by Quadruple H-Bonding. Journal of the American Chemical Society Liu, K. n., Cheng, L. n., Zhang, N. n., Pan, H. n., Fan, X. n., Li, G. n., Zhang, Z. n., Zhao, D. n., Zhao, J. n., Yang, X. n., Wang, Y. n., Bai, R. n., Liu, Y. n., Liu, Z. n., Wang, S. n., Gong, X. n., Bao, Z. n., Gu, G. n., Yu, W. n., Yan, X. n. 2020

  Abstract

  Nature has been inspiring scientists to fabricate impact protective materials for applications in various aspects. However, it is still challenging to integrate flexible, stiffness-changeable, and protective properties into a single polymer, although these merits are of great interest in many burgeoning areas. Herein, we report an impact-protective supramolecular polymeric material (SPM) with unique impact-hardening and reversible stiffness-switching characteristics by mimicking sea cucumber dermis. The emergence of softness-stiffness switchability and subsequent protective properties relies on the dynamic aggregation of the nanoscale hard segments in soft transient polymeric networks modulated by quadruple H-bonding. As such, we demonstrate that our SPM could efficiently reduce the impact force and increase the buffer time of the impact. Importantly, we elucidate the underlying mechanism behind the impact hardening and energy dissipation in our SPM. Based on these findings, we fabricate impact- and puncture-resistant demos to show the potential of our SPM for protective applications.

  View details for DOI 10.1021/jacs.0c12119

  View details for PubMedID 33382241

• Genetically targeted chemical assembly of functional materials in living cells, tissues, and animals. Science (New York, N.Y.) Liu, J. n., Kim, Y. S., Richardson, C. E., Tom, A. n., Ramakrishnan, C. n., Birey, F. n., Katsumata, T. n., Chen, S. n., Wang, C. n., Wang, X. n., Joubert, L. M., Jiang, Y. n., Wang, H. n., Fenno, L. E., Tok, J. B., Pașca, S. P., Shen, K. n., Bao, Z. n., Deisseroth, K. n. 2020; 367 (6484): 1372–76

  Abstract

  The structural and functional complexity of multicellular biological systems, such as the brain, are beyond the reach of human design or assembly capabilities. Cells in living organisms may be recruited to construct synthetic materials or structures if treated as anatomically defined compartments for specific chemistry, harnessing biology for the assembly of complex functional structures. By integrating engineered-enzyme targeting and polymer chemistry, we genetically instructed specific living neurons to guide chemical synthesis of electrically functional (conductive or insulating) polymers at the plasma membrane. Electrophysiological and behavioral analyses confirmed that rationally designed, genetically targeted assembly of functional polymers not only preserved neuronal viability but also achieved remodeling of membrane properties and modulated cell type-specific behaviors in freely moving animals. This approach may enable the creation of diverse, complex, and functional structures and materials within living systems.

  View details for DOI 10.1126/science.aay4866

  View details for PubMedID 32193327

• Artificial multimodal receptors based on ion relaxation dynamics. Science (New York, N.Y.) You, I. n., Mackanic, D. G., Matsuhisa, N. n., Kang, J. n., Kwon, J. n., Beker, L. n., Mun, J. n., Suh, W. n., Kim, T. Y., Tok, J. B., Bao, Z. n., Jeong, U. n. 2020; 370 (6519): 961–65

  Abstract

  Human skin has different types of tactile receptors that can distinguish various mechanical stimuli from temperature. We present a deformable artificial multimodal ionic receptor that can differentiate thermal and mechanical information without signal interference. Two variables are derived from the analysis of the ion relaxation dynamics: the charge relaxation time as a strain-insensitive intrinsic variable to measure absolute temperature and the normalized capacitance as a temperature-insensitive extrinsic variable to measure strain. The artificial receptor with a simple electrode-electrolyte-electrode structure simultaneously detects temperature and strain by measuring the variables at only two measurement frequencies. The human skin-like multimodal receptor array, called multimodal ion-electronic skin (IEM-skin), provides real-time force directions and strain profiles in various tactile motions (shear, pinch, spread, torsion, and so on).

  View details for DOI 10.1126/science.aba5132

  View details for PubMedID 33214277

• Intrinsically stretchable electrode array enabled in vivo electrophysiological mapping of atrial fibrillation at cellular resolution. Proceedings of the National Academy of Sciences of the United States of America Liu, J. n., Zhang, X. n., Liu, Y. n., Rodrigo, M. n., Loftus, P. D., Aparicio-Valenzuela, J. n., Zheng, J. n., Pong, T. n., Cyr, K. J., Babakhanian, M. n., Hasi, J. n., Li, J. n., Jiang, Y. n., Kenney, C. J., Wang, P. J., Lee, A. M., Bao, Z. n. 2020

  Abstract

  Electrophysiological mapping of chronic atrial fibrillation (AF) at high throughput and high resolution is critical for understanding its underlying mechanism and guiding definitive treatment such as cardiac ablation, but current electrophysiological tools are limited by either low spatial resolution or electromechanical uncoupling of the beating heart. To overcome this limitation, we herein introduce a scalable method for fabricating a tissue-like, high-density, fully elastic electrode (elastrode) array capable of achieving real-time, stable, cellular level-resolution electrophysiological mapping in vivo. Testing with acute rabbit and porcine models, the device is proven to have robust and intimate tissue coupling while maintaining its chemical, mechanical, and electrical properties during the cardiac cycle. The elastrode array records epicardial atrial signals with comparable efficacy to currently available endocardial-mapping techniques but with 2 times higher atrial-to-ventricular signal ratio and >100 times higher spatial resolution and can reliably identify electrical local heterogeneity within an area of simultaneously identified rotor-like electrical patterns in a porcine model of chronic AF.

  View details for DOI 10.1073/pnas.2000207117

  View details for PubMedID 32541030

• A Highly Stretchable and Self-Healing Supramolecular Elastomer Based on Sliding Crosslinks and Hydrogen Bonds ADVANCED FUNCTIONAL MATERIALS Du, R., Xu, Z., Zhu, C., Jiang, Y., Yan, H., Wu, H., Vardoulis, O., Cai, Y., Zhu, X., Bao, Z., Zhang, Q., Jia, X. 2019

  View details for DOI 10.1002/adfm.201907139

  View details for Web of Science ID 000503752500001

• Fine-Tuning Semiconducting Polymer Self-Aggregation and Crystallinity Enables Optimal Morphology and High-Performance Printed All-Polymer Solar Cells. Journal of the American Chemical Society Wu, Y., Schneider, S., Walter, C., Chowdhury, A. H., Bahrami, B., Wu, H., Qiao, Q., Toney, M. F., Bao, Z. 2019

  Abstract

  Polymer aggregation and crystallization behavior play a crucial role in the performance of all-polymer solar cells (all-PSCs). Gaining control over polymer self-assembly via molecular design to influence bulk-heterojunction active-layer morphology, however, remains challenging. Herein, we show a simple yet effective way to modulate the self-aggregation of the commonly used naphthalene diimide (NDI)-based acceptor polymer (N2200), by systematically replacing a certain amount of alkyl side-chains with compact bulky side-chains (CBS). Specifically, we have synthesized a series of random copolymer (PNDI-CBSx) with different molar fractions (x = 0-1) of the CBS units and have found that both solution-phase aggregation and solid-state crystallinity of these acceptor polymers are progressively suppressed with increasing x as evidenced by UV-vis absorption, photoluminescence (PL) spectroscopies, thermal analysis, and grazing incidence X-ray scattering (GIWAXS) techniques. Importantly, as compared to the highly self-aggregating N2200, photovoltaic results show that blending of more amorphous acceptor polymers with donor polymer (PBDB-T) can enable all-PSCs with significantly increased PCE (up to 8.5%). The higher short-circuit current density (Jsc) results from the smaller polymer phase-separation domain sizes as evidenced by PL quenching and resonant soft X-ray scattering (R-SoXS) analyses. Additionally, we show that the lower crystallinity of the active layer is less sensitive to the film deposition methods. Thus, the transition from spin-coating to solution coating can be easily achieved with no performance losses. On the other hand, decreasing aggregation and crystallinity of the acceptor polymer too much reduces the photovoltaic performance as the donor phase-separation domain sizes increases. The highly amorphous acceptor polymers appear to induce formation of larger donor polymer crystallites. These results highlight the importance of a balanced aggregation strength between the donor and acceptor polymers to achieve high-performance all-PSCs with optimal active layer film morphology.

  View details for DOI 10.1021/jacs.9b10935

  View details for PubMedID 31793773

• Decoupling of mechanical properties and ionic conductivity in supramolecular lithium ion conductors. Nature communications Mackanic, D. G., Yan, X., Zhang, Q., Matsuhisa, N., Yu, Z., Jiang, Y., Manika, T., Lopez, J., Yan, H., Liu, K., Chen, X., Cui, Y., Bao, Z. 2019; 10 (1): 5384

  Abstract

  The emergence of wearable electronics puts batteries closer to the human skin, exacerbating the need for battery materials that are robust, highly ionically conductive, and stretchable. Herein, we introduce a supramolecular design as an effective strategy to overcome the canonical tradeoff between mechanical robustness and ionic conductivity in polymer electrolytes. The supramolecular lithium ion conductor utilizes orthogonally functional H-bonding domains and ion-conducting domains to create a polymer electrolyte with unprecedented toughness (29.3 MJ m-3) and high ionic conductivity (1.2*10-4 S cm-1 at 25°C). Implementation of the supramolecular ion conductor as a binder material allows for the creation of stretchable lithium-ion battery electrodes with strain capability of over 900% via a conventional slurry process. The supramolecular nature of these battery components enables intimate bonding at the electrode-electrolyte interface. Combination of these stretchable components leads to a stretchable battery with a capacity of 1.1 mAh cm-2 that functions even when stretched to 70% strain. The method reported here of decoupling ionic conductivity from mechanical properties opens a promising route to create high-toughness ion transport materials for energy storage applications.

  View details for DOI 10.1038/s41467-019-13362-4

  View details for PubMedID 31772158

• A Dynamic, Electrolyte-Blocking, and Single-Ion-Conductive Network for Stable Lithium-Metal Anodes JOULE Yu, Z., Mackanic, D. G., Michaels, W., Lee, M., Pei, A., Feng, D., Zhang, Q., Tsao, Y., Amanchukwu, C., Yan, X., Wang, H., Chen, S., Liu, K., Kang, J., Qin, J., Cui, Y., Bao, Z. 2019; 3 (11): 2761–76

  View details for DOI 10.1016/j.joule.2019.07.025

  View details for Web of Science ID 000497987900018

• Stretchable self-healable semiconducting polymer film for active-matrix strain-sensing array. Science advances Oh, J. Y., Son, D., Katsumata, T., Lee, Y., Kim, Y., Lopez, J., Wu, H., Kang, J., Park, J., Gu, X., Mun, J., Wang, N. G., Yin, Y., Cai, W., Yun, Y., Tok, J. B., Bao, Z. 2019; 5 (11): eaav3097

  Abstract

  Skin-like sensory devices should be stretchable and self-healable to meet the demands for future electronic skin applications. Despite recent notable advances in skin-inspired electronic materials, it remains challenging to confer these desired functionalities to an active semiconductor. Here, we report a strain-sensitive, stretchable, and autonomously self-healable semiconducting film achieved through blending of a polymer semiconductor and a self-healable elastomer, both of which are dynamically cross-linked by metal coordination. We observed that by controlling the percolation threshold of the polymer semiconductor, the blend film became strain sensitive, with a gauge factor of 5.75 * 105 at 100% strain in a stretchable transistor. The blend film is also highly stretchable (fracture strain, >1300%) and autonomously self-healable at room temperature. We proceed to demonstrate a fully integrated 5 * 5 stretchable active-matrix transistor sensor array capable of detecting strain distribution through surface deformation.

  View details for DOI 10.1126/sciadv.aav3097

  View details for PubMedID 31723597

• A Novel Technology for Free Flap Monitoring: Pilot Study of a Wireless, Biodegradable Sensor. Journal of reconstructive microsurgery Oda, H., Beker, L., Kaizawa, Y., Franklin, A., Min, J. G., Leyden, J., Wang, Z., Chang, J., Bao, Z., Fox, P. M. 2019

  Abstract

  BACKGROUND: Accurate monitoring of free flap perfusion after complex reconstruction is critical for early recognition of flap compromise. Surgeons use a variety of subjective and objective measures to evaluate flap perfusion postoperatively. However, these measures have some limitations. We have developed a wireless, biodegradable, and flexible sensor that can be applied to real-time postoperative free flap monitoring. Here we assess the biocompatibility and function of our novel sensor.METHODS: Seven Sprague-Dawley (SD) rats were used for biocompatibility studies. The sensor was implanted around the femoral artery near the inguinal ligament on one leg (implant side) and sham surgery was performed on the contralateral leg (control side). At 6 and 12 weeks, samples were harvested to assess the inflammation within and around the implant and artery. Two animals were used to assess sensor function. Sensor function was evaluated at implantation and 7 days after the implantation. Signal changes after venous occlusion were also assessed in an epigastric artery island flap model.RESULTS: In biocompatibility studies, the diameter of the arterial lumen and intima thickness in the implant group were not significantly different than the control group at the 12-week time point. The number of CD-68 positive cells that infiltrated into the soft tissue, surrounding the femoral artery, was also not significantly different between groups at the 12-week time point. For sensor function, accurate signaling could be recorded at implantation and 7 days later. A change in arterial signal was noted immediately after venous occlusion in a flap model.CONCLUSION: The novel wireless, biodegradable sensor presented here is biocompatible and capable of detecting arterial blood flow and venous occlusion with high sensitivity. This promising new technology could combat the complications of wired sensors, while improving the survival rate of flaps with vessel compromise due to its responsive nature.

  View details for DOI 10.1055/s-0039-1700539

  View details for PubMedID 31675757

• Effect of Extensional Flow on the Evaporative Assembly of a Donor-Acceptor Semiconducting Polymer ACS APPLIED ELECTRONIC MATERIALS Nikzad, S., Wu, H., Wang, G., Yan, H., Schneider, S. A., Toney, M. F., Bao, Z. 2019; 1 (11): 2445–54

  View details for DOI 10.1021/acsaelm.9b00576

  View details for Web of Science ID 000500038600032

• Intrinsically Stretchable Temperature Sensor Based on Organic Thin-Film Transistors IEEE ELECTRON DEVICE LETTERS Zhu, C., Wu, H., Nyikayaramba, G., Bao, Z., Murmann, B. 2019; 40 (10): 1630–33

  View details for DOI 10.1109/LED.2019.2933838

  View details for Web of Science ID 000489740400016

• The Microbead: A 0.009 mm(3) Implantable Wireless Neural Stimulator IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS Khalifa, A., Liu, Y., Karimi, Y., Wang, Q., Eisape, A., Stanacevic, M., Thakor, N., Bao, Z., Etienne-Cummings, R. 2019; 13 (5): 971–85

  Abstract

  Wirelessly powered implants are increasingly being developed to interface with neurons in the brain. They often rely on microelectrode arrays, which are limited by their ability to cover large cortical surface areas and long-term stability because of their physical size and rigid configuration. Yet some clinical and research applications prioritize a distributed neural interface over one that offers high channel count. One solution to make large scale, fully specifiable, electrical stimulation/recording possible, is to disconnect the electrodes from the base, so that they can be arbitrarily placed freely in the nervous system. In this work, a wirelessly powered stimulating implant is miniaturized using a novel electrode integration technique, and its implanted depth maximized using new optimization design methods for the transmitter and receiver coils. The stimulating device is implemented in a 130 nm CMOS technology with the following characteristics: 300 μm × 300 μm × 80 μm size; optimized two-coil inductive link; and integrated circuit, electrodes and coil. The wireless and stimulation capability of the implant is demonstrated in a conductive medium, as well as in-vivo. To the best of our knowledge, the fabricated free-floating miniaturized implant has the best depth-to-volume ratio making it an excellent tool for minimally-invasive distributed neural interface, and thus could eventually complement or replace the rigid arrays that are currently the state-of-the-art in brain set-ups.

  View details for DOI 10.1109/TBCAS.2019.2939014

  View details for Web of Science ID 000498642200019

  View details for PubMedID 31484132

• Nonpolar Alkanes Modify Lithium-Ion Solvation for Improved Lithium Deposition and Stripping ADVANCED ENERGY MATERIALS Amanchukwu, C., Kong, X., Qin, J., Cui, Y., Bao, Z. 2019

  View details for DOI 10.1002/aenm.201902116

  View details for Web of Science ID 000487515200001

• An Intrinsically Stretchable High-Performance Polymer Semiconductor with Low Crystallinity ADVANCED FUNCTIONAL MATERIALS Zheng, Y., Wang, G., Kang, J., Nikolka, M., Wu, H., Tran, H., Zhang, S., Yan, H., Chen, H., Yuen, P., Mun, J., Dauskardt, R. H., McCulloch, I., Tok, J., Gu, X., Bao, Z. 2019

  View details for DOI 10.1002/adfm.201905340

  View details for Web of Science ID 000486591200001

• Tuning the Cross-Linker Crystallinity of a Stretchable Polymer Semiconductor CHEMISTRY OF MATERIALS Wang, G., Zheng, Y., Zhang, S., Kang, J., Wu, H., Gasperini, A., Zhang, H., Gu, X., Bao, Z. 2019; 31 (17): 6465–75

  View details for DOI 10.1021/acs.chemmater.8b04314

  View details for Web of Science ID 000485830300013

• An Electrochemical Gelation Method for Patterning Conductive PEDOT:PSS Hydrogels. Advanced materials (Deerfield Beach, Fla.) Feig, V. R., Tran, H., Lee, M., Liu, K., Huang, Z., Beker, L., Mackanic, D. G., Bao, Z. 2019: e1902869

  Abstract

  Due to their high water content and macroscopic connectivity, hydrogels made from the conducting polymer PEDOT:PSS are a promising platform from which to fabricate a wide range of porous conductive materials that are increasingly of interest in applications as varied as bioelectronics, regenerative medicine, and energy storage. Despite the promising properties of PEDOT:PSS-based porous materials, the ability to pattern PEDOT:PSS hydrogels is still required to enable their integration with multifunctional and multichannel electronic devices. In this work, a novel electrochemical gelation ("electrogelation") method is presented for rapidly patterning PEDOT:PSS hydrogels on any conductive template, including curved and 3D surfaces. High spatial resolution is achieved through use of a sacrificial metal layer to generate the hydrogel pattern, thereby enabling high-performance conducting hydrogels and aerogels with desirable material properties to be introduced into increasingly complex device architectures.

  View details for DOI 10.1002/adma.201902869

  View details for PubMedID 31414520

• A wireless body area sensor network based on stretchable passive tags NATURE ELECTRONICS Niu, S., Matsuhisa, N., Beker, L., Li, J., Wang, S., Wang, J., Jiang, Y., Yan, X., Yuri, Y., Burnetts, W., Poon, A. Y., Tok, J., Chen, X., Bao, Z. 2019; 2 (8): 361–68

  View details for DOI 10.1038/s41928-019-0286-2

  View details for Web of Science ID 000481640000014

• High-Transconductance Stretchable Transistors Achieved by Controlled Gold Microcrack Morphology ADVANCED ELECTRONIC MATERIALS Matsuhisa, N., Jiang, Y., Liu, Z., Chen, G., Wan, C., Kim, Y., Kang, J., Tran, H., Wu, H., You, I., Bao, Z., Chen, X. 2019; 5 (8)

  View details for DOI 10.1002/aelm.201900347

  View details for Web of Science ID 000479319100023

• Strain- and Strain-Rate-Invariant Conductance in a Stretchable and Compressible 3D Conducting Polymer Foam MATTER Chen, G., Rastak, R., Wang, Y., Yan, H., Feig, V., Liu, Y., Jiang, Y., Chen, S., Lian, F., Molina-Lopez, F., Jin, L., Cui, K., Chung, J., Pop, E., Linder, C., Bao, Z. 2019; 1 (1): 205–18

  View details for DOI 10.1016/j.matt.2019.03.011

  View details for Web of Science ID 000519687800022

• Compact Modeling of Thin-Film Transistors for Flexible Hybrid IoT Design IEEE DESIGN & TEST Shao, L., Lei, T., Huang, T., Li, S., Chu, T., Wong, M., Beausoleil, R., Bao, Z., Cheng, K. 2019; 36 (4): 6–14

  View details for DOI 10.1109/MDAT.2019.2899058

  View details for Web of Science ID 000476811500003

• Polymer Chemistries Underpinning Materials for Skin-Inspired Electronics MACROMOLECULES Tran, H., Feig, V. R., Liu, K., Zheng, Y., Bao, Z. 2019; 52 (11): 3965–74

  View details for DOI 10.1021/acs.macromol.9b00410

  View details for Web of Science ID 000471729000001

• Materials and structural designs of stretchable conductors CHEMICAL SOCIETY REVIEWS Matsuhisa, N., Chen, X., Bao, Z., Someya, T. 2019; 48 (11): 2946–66

  View details for DOI 10.1039/c8cs00814k

  View details for Web of Science ID 000470929900002

• Second Skin Enabled by Advanced Electronics. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Oh, J. Y., Bao, Z. 2019; 6 (11): 1900186

  Abstract

  Electronic second skin is touted as the next interface to expand applications of electronics for natural and seamless interactions with humans to enable smart health care, the Internet of Things, and even to amplify human sensory abilities. Thus, electronic materials are now being actively investigated to construct "second skin." Accordingly, electronic devices are desirable to have skin-like properties such as stretchability, self-healing ability, biocompatibility, and biodegradability. This work reviews recent major progress in the development of both electronic materials and devices toward the second skin. It is concluded with comments on future research directions of the field.

  View details for DOI 10.1002/advs.201900186

  View details for PubMedID 31179225

• An Ultrastretchable and Self-Healable Nanocomposite Conductor Enabled by Autonomously Percolative Electrical Pathways ACS NANO Kim, S., Seo, H., Kang, J., Hong, J., Seong, D., Kim, H., Kim, J., Mun, J., Youn, I., Kim, J., Kim, Y., Seok, H., Lee, C., Tok, J., Bao, Z., Son, D. 2019; 13 (6): 6531–39

  View details for DOI 10.1021/acsnano.9b00160

  View details for Web of Science ID 000473248300039

• Multi-scale ordering in highly stretchable polymer semiconducting films NATURE MATERIALS Xu, J., Wu, H., Zhu, C., Ehrlich, A., Shaw, L., Nikolka, M., Wang, S., Molina-Lopez, F., Gu, X., Luo, S., Zhou, D., Kim, Y., Wang, G., Gu, K., Feig, V., Chen, S., Kim, Y., Katsumata, T., Zheng, Y., Yan, H., Chung, J., Lopez, J., Murmann, B., Bao, Z. 2019; 18 (6): 594-+

  View details for DOI 10.1038/s41563-019-0340-5

  View details for Web of Science ID 000468511800018

• Low-voltage high-performance flexible digital and analog circuits based on ultrahigh-purity semiconducting carbon nanotubes NATURE COMMUNICATIONS Lei, T., Shao, L., Zheng, Y., Pitner, G., Fang, G., Zhu, C., Li, S., Beausoleil, R., Wong, H., Huang, T., Cheng, K., Bao, Z. 2019; 10

  View details for DOI 10.1038/s41467-019-10145-9

  View details for Web of Science ID 000467837200001

• An Ultrastretchable and Self-Healable Nanocomposite Conductor Enabled by Autonomously Percolative Electrical Pathways. ACS nano Kim, S. H., Seo, H., Kang, J., Hong, J., Seong, D., Kim, H., Kim, J., Mun, J., Youn, I., Kim, J., Kim, Y., Seok, H., Lee, C., Tok, J. B., Bao, Z., Son, D. 2019

  Abstract

  Both self-healable conductors and stretchable conductors have been previously reported. However, it is still difficult to simultaneously achieve high stretchability, high conductivity, and self-healability. Here, we observed an intriguing phenomenon, termed "electrical self-boosting", which enables reconstructing of electrically percolative pathways in an ultrastretchable and self-healable nanocomposite conductor (over 1700% strain). The autonomously reconstructed percolative pathways were directly verified by using microcomputed tomography and in situ scanning electron microscopy. The encapsulated nanocomposite conductor shows exceptional conductivity (average value: 2578 S cm-1; highest value: 3086 S cm-1) at 3500% tensile strain by virtue of efficient strain energy dissipation of the self-healing polymer and self-alignment and rearrangement of silver flakes surrounded by spontaneously formed silver nanoparticles and their self-assembly in the strained self-healing polymer matrix. In addition, the conductor maintains high conductivity and stretchability even after recovered from a complete cut. Besides, a design of double-layered conductor enabled by the self-bonding assembly allowed a conducting interface to be located on the neutral mechanical plane, showing extremely durable operations in a cyclic stretching test. Finally, we successfully demonstrated that electromyogram signals can be monitored by our self-healable interconnects. Such information was transmitted to a prosthetic robot to control various hand motions for robust interactive human-robot interfaces.

  View details for PubMedID 31072094

• High-Rate and Large-Capacity Lithium Metal Anode Enabled by Volume Conformal and Self-Healable Composite Polymer Electrolyte ADVANCED SCIENCE Xia, S., Lopez, J., Liang, C., Zhang, Z., Bao, Z., Cui, Y., Liu, W. 2019; 6 (9)

  View details for DOI 10.1002/advs.201802353

  View details for Web of Science ID 000467524500005

• Designing polymers for advanced battery chemistries NATURE REVIEWS MATERIALS Lopez, J., Mackanic, D. G., Cui, Y., Bao, Z. 2019; 4 (5): 312–30

  View details for DOI 10.1038/s41578-019-0103-6

  View details for Web of Science ID 000467301000006

• Multi-scale ordering in highly stretchable polymer semiconducting films. Nature materials Xu, J., Wu, H., Zhu, C., Ehrlich, A., Shaw, L., Nikolka, M., Wang, S., Molina-Lopez, F., Gu, X., Luo, S., Zhou, D., Kim, Y., Wang, G. N., Gu, K., Feig, V. R., Chen, S., Kim, Y., Katsumata, T., Zheng, Y., Yan, H., Chung, J. W., Lopez, J., Murmann, B., Bao, Z. 2019

  Abstract

  Stretchable semiconducting polymers have been developed as a key component to enable skin-like wearable electronics, but their electrical performance must be improved to enable more advanced functionalities. Here, we report a solution processing approach that can achieve multi-scale ordering and alignment of conjugated polymers in stretchable semiconductors to substantially improve their charge carrier mobility. Using solution shearing with a patterned microtrench coating blade, macroscale alignment of conjugated-polymer nanostructures was achieved along the charge transport direction. In conjunction, the nanoscale spatial confinement aligns chain conformation and promotes short-range pi-pi ordering, substantially reducing the energetic barrier for charge carrier transport. As a result, the mobilities of stretchable conjugated-polymer films have been enhanced up to threefold and maintained under a strain up to 100%. This method may also serve as the basis for large-area manufacturing of stretchable semiconducting films, as demonstrated by the roll-to-roll coating of metre-scale films.

  View details for PubMedID 30988452

• Self-healing soft electronics NATURE ELECTRONICS Kang, J., Tok, J., Bao, Z. 2019; 2 (4): 144–50

  View details for DOI 10.1038/s41928-019-0235-0

  View details for Web of Science ID 000465035400008

• Effects of polymer coatings on electrodeposited lithium metal Lopez, J., Pei, A., Cui, Y., Bao, Z. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478860505895

• Electrochemical patterning of tissue-mimetic conductive hydrogels Feig, V., Tran, H., Lee, M., Huang, R., Liu, K., Baker, L., Mackanic, D., Bao, Z. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478861205318

• Facile synthesis of carbon flower particles from a novel polyacrylonitrile system Chen, S., Bao, Z. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478861205541

• Characterization of Hydrogen Bonding Formation and Breaking in Semiconducting Polymers under Mechanical Strain MACROMOLECULES Gasperini, A., Wang, G., Molina-Lopez, F., Wu, H., Lopez, J., Xu, J., Luo, S., Zhou, D., Xue, G., Tok, J., Bao, Z. 2019; 52 (6): 2476–86

  View details for DOI 10.1021/acs.macromol.9b00145

  View details for Web of Science ID 000462950300026

• Designing a Quinone-Based Redox Mediator to Facilitate Li2S Oxidation in Li-S Batteries JOULE Tsao, Y., Lee, M., Miller, E. C., Gao, G., Park, J., Chen, S., Katsumata, T., Tran, H., Wang, L., Toney, M. F., Cui, Y., Bao, Z. 2019; 3 (3): 872–84

  View details for DOI 10.1016/j.joule.2018.12.018

  View details for Web of Science ID 000462010600022

• Wearable Bioelectronics: Opportunities for Chemistry. Accounts of chemical research Rogers, J., Bao, Z., Lee, T. 2019; 52 (3): 521–22

  View details for PubMedID 30884949

• Thermodynamically stable whilst kinetically labile coordination bonds lead to strong and tough self-healing polymers NATURE COMMUNICATIONS Lai, J., Jia, X., Wang, D., Deng, Y., Zheng, P., Li, C., Zuo, J., Bao, Z. 2019; 10

  View details for DOI 10.1038/s41467-019-09130-z

  View details for Web of Science ID 000460759800014

• Thermodynamically stable whilst kinetically labile coordination bonds lead to strong and tough self-healing polymers. Nature communications Lai, J., Jia, X., Wang, D., Deng, Y., Zheng, P., Li, C., Zuo, J., Bao, Z. 2019; 10 (1): 1164

  Abstract

  There is often a trade-off between mechanical properties (modulus and toughness) and dynamic self-healing. Here we report the design and synthesis of a polymer containing thermodynamically stable whilst kinetically labile coordination complex to address this conundrum. The Zn-Hbimcp (Hbimcp=2,6-bis((imino)methyl)-4-chlorophenol) coordination bond used in this work has a relatively large association constant (2.2*1011) but also undergoes fast and reversible intra- and inter-molecular ligand exchange processes. The as-prepared Zn(Hbimcp)2-PDMS polymer is highly stretchable (up to 2400% strain) with a high toughness of 29.3MJm-3, and canautonomously self-heal at room temperature. Control experiments showed that the optimal combination of its bond strength and bond dynamics is responsible for the material's mechanical toughness and self-healing property. This molecular design concept points out a promising direction for the preparation of self-healing polymers with excellent mechanical properties. We further show this type of polymer can be potentially used as energy absorbing material.

  View details for PubMedID 30858371

• Pathways for practical high-energy long-cycling lithium metal batteries NATURE ENERGY Liu, J., Bao, Z., Cui, Y., Dufek, E. J., Goodenough, J. B., Khalifah, P., Li, Q., Liaw, B., Liu, P., Manthiram, A., Meng, Y., Subramanian, V. R., Toney, M. F., Viswanathan, V. V., Whittingham, M., Xiao, J., Xu, W., Yang, J., Yang, X., Zhang, J. 2019; 4 (3): 180–86

  View details for DOI 10.1038/s41560-019-0338-x

  View details for Web of Science ID 000461124600009

• Wearable Bioelectronics: Opportunities for Chemistry ACCOUNTS OF CHEMICAL RESEARCH Rogers, J., Bao, Z., Lee, T. 2019; 52 (3): 521-522

  View details for DOI 10.1021/acs.accounts.9b00048

  View details for Web of Science ID 000462098100001

• Molecular parameters responsible for thermally activated transport in doped organic semiconductors NATURE MATERIALS Schwarze, M., Gaul, C., ScholZ, R., Bussolotti, F., Hofacker, A., Schellhammer, K., Nell, B., Naab, B. D., Bao, Z., Spoltore, D., Vandewal, K., Widmer, J., Kera, S., Ueno, N., Ortmann, F., Leo, K. 2019; 18 (3): 242-+

  View details for DOI 10.1038/s41563-018-0277-0

  View details for Web of Science ID 000459017900016

• Modular and Reconfigurable Stretchable Electronic Systems ADVANCED MATERIALS TECHNOLOGIES Kang, J., Son, D., Vardoulis, O., Mun, J., Matsuhisa, N., Kim, Y., Kim, J., Tok, J., Bao, Z. 2019; 4 (3)

  View details for DOI 10.1002/admt.201800417

  View details for Web of Science ID 000461232400019

• Molecular parameters responsible for thermally activated transport in doped organic semiconductors. Nature materials Schwarze, M., Gaul, C., Scholz, R., Bussolotti, F., Hofacker, A., Schellhammer, K. S., Nell, B., Naab, B. D., Bao, Z., Spoltore, D., Vandewal, K., Widmer, J., Kera, S., Ueno, N., Ortmann, F., Leo, K. 2019

  Abstract

  Doped organic semiconductors typically exhibit a thermal activation of their electrical conductivity, whose physical origin is still under scientific debate. In this study, we disclose relationships between molecular parameters and the thermal activation energy (EA) of the conductivity, revealing that charge transport is controlled by the properties of host-dopant integer charge transfer complexes (ICTCs) in efficiently doped organic semiconductors. At low doping concentrations, charge transport is limited by the Coulomb binding energy of ICTCs, which can be minimized by systematic modification of the charge distribution on the individual ions. The investigation of a wide variety of material systems reveals that static energetic disorder induced by ICTC dipole moments sets a general lower limit for EA at large doping concentrations. The impact of disorder can be reduced by adjusting the ICTC density and the intramolecular relaxation energy of host ions, allowing an increase of conductivity by many orders of magnitude.

  View details for PubMedID 30692647

• Disassociation and Reformation Under Strain in Polymer with Dynamic Metal-Ligand Coordination Cross-Linking MACROMOLECULES Zhang, Q., Zhu, X., Li, C., Cai, Y., Jia, X., Bao, Z. 2019; 52 (2): 660–68

  View details for DOI 10.1021/acs.macromol.8b02414

  View details for Web of Science ID 000456749500025

• Materials and structural designs of stretchable conductors. Chemical Society reviews Matsuhisa, N. n., Chen, X. n., Bao, Z. n., Someya, T. n. 2019

  Abstract

  Stretchable conductors are essential building blocks for stretchable electronic devices used in next-generation wearables and soft robotics. Over 10 years of research in stretchable electronics has produced stretchable sensors, circuits, displays, and energy harvesters, mostly enabled by unique stretchable conductors. This review covers recent advances in stretchable conductors, which have been achieved by engineering their structures, materials, or both. Advantages, mechanisms, and limitations of the different classes of stretchable conductors are discussed to provide insight into which class of stretchable conductor is suitable for fabrication of various stretchable electronic devices. The significantly improved electronic performance and wide variety of stretchable conductors are creating a new paradigm in stretchable electronics.

  View details for PubMedID 31073551

• Electronic Skin: Recent Progress and Future Prospects for Skin-Attachable Devices for Health Monitoring, Robotics, and Prosthetics. Advanced materials (Deerfield Beach, Fla.) Yang, J. C., Mun, J. n., Kwon, S. Y., Park, S. n., Bao, Z. n., Park, S. n. 2019: e1904765

  Abstract

  Recent progress in electronic skin or e-skin research is broadly reviewed, focusing on technologies needed in three main applications: skin-attachable electronics, robotics, and prosthetics. First, since e-skin will be exposed to prolonged stresses of various kinds and needs to be conformally adhered to irregularly shaped surfaces, materials with intrinsic stretchability and self-healing properties are of great importance. Second, tactile sensing capability such as the detection of pressure, strain, slip, force vector, and temperature are important for health monitoring in skin attachable devices, and to enable object manipulation and detection of surrounding environment for robotics and prosthetics. For skin attachable devices, chemical and electrophysiological sensing and wireless signal communication are of high significance to fully gauge the state of health of users and to ensure user comfort. For robotics and prosthetics, large-area integration on 3D surfaces in a facile and scalable manner is critical. Furthermore, new signal processing strategies using neuromorphic devices are needed to efficiently process tactile information in a parallel and low power manner. For prosthetics, neural interfacing electrodes are of high importance. These topics are discussed, focusing on progress, current challenges, and future prospects.

  View details for DOI 10.1002/adma.201904765

  View details for PubMedID 31538370

• Stretchable and Fully Degradable Semiconductors for Transient Electronics. ACS central science Tran, H. n., Feig, V. R., Liu, K. n., Wu, H. C., Chen, R. n., Xu, J. n., Deisseroth, K. n., Bao, Z. n. 2019; 5 (11): 1884–91

  Abstract

  The next materials challenge in organic stretchable electronics is the development of a fully degradable semiconductor that maintains stable electrical performance under strain. Herein, we decouple the design of stretchability and transience by harmonizing polymer physics principles and molecular design in order to demonstrate for the first time a material that simultaneously possesses three disparate attributes: semiconductivity, intrinsic stretchability, and full degradability. We show that we can design acid-labile semiconducting polymers to appropriately phase segregate within a biodegradable elastomer, yielding semiconducting nanofibers that concurrently enable controlled transience and strain-independent transistor mobilities. Along with the future development of suitable conductors and device integration advances, we anticipate that these materials could be used to build fully biodegradable diagnostic or therapeutic devices that reside inside the body temporarily, or environmental monitors that are placed in the field and break down when they are no longer needed. This fully degradable semiconductor represents a promising advance toward developing multifunctional materials for skin-inspired electronic devices that can address previously inaccessible challenges and in turn create new technologies.

  View details for DOI 10.1021/acscentsci.9b00850

  View details for PubMedID 31807690

  View details for PubMedCentralID PMC6891860

• Process Design Kit and Design Automation for Flexible Hybrid Electronics Huang, T., Lei, T., Shao, L., Sivapurapu, S., Swaminathan, M., Li, S., Bao, Z., Cheng, K., Beausoleil, R., IEEE IEEE. 2019

  View details for Web of Science ID 000480385400032

• Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation NATURE BIOMEDICAL ENGINEERING Liu, Y., Liu, J., Chen, S., Lei, T., Kim, Y., Niu, S., Wang, H., Wang, X., Foudeh, A. M., Tok, J., Bao, Z. 2019; 3 (1): 58–68

  View details for DOI 10.1038/s41551-018-0335-6

  View details for Web of Science ID 000455123800012

• Biodegradable and flexible arterial-pulse sensor for the wireless monitoring of blood flow NATURE BIOMEDICAL ENGINEERING Boutry, C. M., Beker, L., Kaizawa, Y., Vassos, C., Tran, H., Hinckley, A. C., Pfattner, R., Niu, S., Li, J., Claverie, J., Wang, Z., Chang, J., Fox, P. M., Bao, Z. 2019; 3 (1): 47–57

  View details for DOI 10.1038/s41551-018-0336-5

  View details for Web of Science ID 000455123800011

• Ultra-thin Skin Electronics for High Quality and Continuous Skin-Sensor-Silicon Interfacing Shao, L., Li, S., Lei, T., Huang, T., Beausoleil, R., Bao, Z., Cheng, K., ACM ASSOC COMPUTING MACHINERY. 2019

  View details for DOI 10.1145/3316781.3317928

  View details for Web of Science ID 000482058200016

• Dual-Gate Organic Field-Effect Transistor for pH Sensors with Tunable Sensitivity ADVANCED ELECTRONIC MATERIALS Pfattner, R., Foudeh, A. M., Chen, S., Niu, W., Matthews, J. R., He, M., Bao, Z. 2019; 5 (1)

  View details for DOI 10.1002/aelm.201800381

  View details for Web of Science ID 000455220900010

• Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation. Nature biomedical engineering Liu, Y., Liu, J., Chen, S., Lei, T., Kim, Y., Niu, S., Wang, H., Wang, X., Foudeh, A. M., Tok, J. B., Bao, Z. 2019; 3 (1): 58-68

  Abstract

  Narrowing the mechanical mismatch between tissue and implantable microelectronics is essential for reducing immune responses and for accommodating body movement. However, the design of implantable soft electronics (on the order of 10 kPa in modulus) remains a challenge because of the limited availability of suitable electronic materials. Here, we report electrically conductive hydrogel-based elastic microelectronics with Young's modulus values in the kilopascal range. The system consists of a highly conductive soft hydrogel as a conductor and an elastic fluorinated photoresist as the passivation insulation layer. Owing to the high volumetric capacitance and the passivation layer of the hydrogel, electrode arrays of the thin-film hydrogel 'elastronics', 20 μm in feature size, show a significantly reduced interfacial impedance with tissue, a current-injection density that is ~30 times higher than that of platinum electrodes, and stable electrical performance under strain. We demonstrate the use of the soft elastronic arrays for localized low-voltage electrical stimulation of the sciatic nerve in live mice.

  View details for DOI 10.1038/s41551-018-0335-6

  View details for PubMedID 30932073

• Biodegradable and flexible arterial-pulse sensor for the wireless monitoring of blood flow. Nature biomedical engineering Boutry, C. M., Beker, L., Kaizawa, Y., Vassos, C., Tran, H., Hinckley, A. C., Pfattner, R., Niu, S., Li, J., Claverie, J., Wang, Z., Chang, J., Fox, P. M., Bao, Z. 2019; 3 (1): 47-57

  Abstract

  The ability to monitor blood flow is critical to patient recovery and patient outcomes after complex reconstructive surgeries. Clinically available wired implantable monitoring technology requires careful fixation for accurate detection and needs to be removed after use. Here, we report the design of a pressure sensor, made entirely of biodegradable materials and based on fringe-field capacitor technology, for measuring arterial blood flow in both contact and non-contact modes. The sensor is operated wirelessly through inductive coupling, has minimal hysteresis, fast response times, excellent cycling stability, is highly robust, allows for easy mounting and eliminates the need for removal, thus reducing the risk of vessel trauma. We demonstrate the operation of the sensor with a custom-made artificial artery model and in vivo in rats. This technology may be advantageous in real-time post-operative monitoring of blood flow after reconstructive surgery.

  View details for DOI 10.1038/s41551-018-0336-5

  View details for PubMedID 30932072

• Low-voltage high-performance flexible digital and analog circuits based on ultrahigh-purity semiconducting carbon nanotubes. Nature communications Lei, T. n., Shao, L. L., Zheng, Y. Q., Pitner, G. n., Fang, G. n., Zhu, C. n., Li, S. n., Beausoleil, R. n., Wong, H. P., Huang, T. C., Cheng, K. T., Bao, Z. n. 2019; 10 (1): 2161

  Abstract

  Carbon nanotube (CNT) thin-film transistor (TFT) is a promising candidate for flexible and wearable electronics. However, it usually suffers from low semiconducting tube purity, low device yield, and the mismatch between p- and n-type TFTs. Here, we report low-voltage and high-performance digital and analog CNT TFT circuits based on high-yield (19.9%) and ultrahigh purity (99.997%) polymer-sorted semiconducting CNTs. Using high-uniformity deposition and pseudo-CMOS design, we demonstrated CNT TFTs with good uniformity and high performance at low operation voltage of 3 V. We tested forty-four 2-µm channel 5-stage ring oscillators on the same flexible substrate (1,056 TFTs). All worked as expected with gate delays of 42.7 ± 13.1 ns. With these high-performance TFTs, we demonstrated 8-stage shift registers running at 50 kHz and the first tunable-gain amplifier with 1,000 gain at 20 kHz. These results show great potentials of using solution-processed CNT TFTs for large-scale flexible electronics.

  View details for PubMedID 31089127

• Process Design Kit and Design Automation for Flexible Hybrid Electronics Huang, T., Lei, T., Shao, L., Sivapurapu, S., Swaminathan, M., Li, S., Bao, Z., Cheng, K., Beausoleil, R., IEEE IEEE. 2019: 36–41

  View details for Web of Science ID 000470666100007

• Conjugated Carbon Cyclic Nanorings as Additives for Intrinsically Stretchable Semiconducting Polymers. Advanced materials (Deerfield Beach, Fla.) Mun, J. n., Kang, J. n., Zheng, Y. n., Luo, S. n., Wu, H. C., Matsuhisa, N. n., Xu, J. n., Wang, G. N., Yun, Y. n., Xue, G. n., Tok, J. B., Bao, Z. n. 2019: e1903912

  Abstract

  Molecular additives are often used to enhance dynamic motion of polymeric chains, which subsequently alter the functional and physical properties of polymers. However, controlling the chain dynamics of semiconducting polymer thin films and understanding the fundamental mechanisms of such changes is a new area of research. Here, cycloparaphenylenes (CPPs) are used as conjugated molecular additives to tune the dynamic behaviors of diketopyrrolopyrrole-based (DPP-based) semiconducting polymers. It is observed that the addition of CPPs results in significant improvement in the stretchability of the DPP-based polymers without adversely affecting their mobility, which arises from the enhanced polymer dynamic motion and reduced long-range crystalline order. The polymer films retain their fiber-like morphology and short-range ordered aggregates, which leads to high mobility. Fully stretchable transistors are subsequently fabricated using CPP/semiconductor composites as active layers. These composites are observed to maintain high mobilities when strained and after repeated applied strains. Interestingly, CPPs are also observed to improve the contact resistance and charge transport of the fully stretchable transistors. ln summary, these results collectively indicate that controlling the dynamic motion of polymer semiconductors is proved to be an effective way to improve their stretchability.

  View details for DOI 10.1002/adma.201903912

  View details for PubMedID 31489716

• High-Rate and Large-Capacity Lithium Metal Anode Enabled by Volume Conformal and Self-Healable Composite Polymer Electrolyte. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Xia, S. n., Lopez, J. n., Liang, C. n., Zhang, Z. n., Bao, Z. n., Cui, Y. n., Liu, W. n. 2019; 6 (9): 1802353

  Abstract

  The widespread implementation of lithium-metal batteries (LMBs) with Li metal anodes of high energy density has long been prevented due to the safety concern of dendrite-related failure. Here a solid-liquid hybrid electrolyte consisting of composite polymer electrolyte (CPE) soaked with liquid electrolyte is reported. The CPE membrane composes of self-healing polymer and Li+-conducting nanoparticles. The electrodeposited lithium metal in a uniform, smooth, and dense behavior is achieved using a hybrid electrolyte, rather than dendritic and pulverized structure for a conventional separator. The Li foil symmetric cells can deliver remarkable cycling performance at ultrahigh current density up to 20 mA cm-2 with an extremely low voltage hysteresis over 1500 cycles. A large areal capacity of 10 mAh cm-2 at 10 mA cm-2 could also be obtained. Furthermore, the Li|Li4Ti5O12 cells based on the hybrid electrolyte achieve a higher specific capacity and longer cycling life than those using conventional separators. The superior performances are mainly attributed to strong adhesion, volume conformity, and self-healing functionality of CPE, providing a novel approach and a significant step toward cost-effective and large-scalable LMBs.

  View details for PubMedID 31065528

• Synthesis and Properties of Soluble Fused Thiophene Diketopyrrolopyrrole-Based Polymers with Tunable Molecular Weight MACROMOLECULES Niu, W., Wu, H., Matthews, J. R., Tandia, A., Li, Y., Wallace, A. L., Kim, J., Wang, H., Li, X., Mehrotra, K., Bao, Z., He, M. 2018; 51 (23): 9422–29

  View details for DOI 10.1021/acs.macromol.8b01760

  View details for Web of Science ID 000453489600002

• Nanomaterials in Skin-Inspired Electronics: Toward Soft and Robust Skin-like Electronic Nanosystems ACS NANO Son, D., Bao, Z. 2018; 12 (12): 11731-11739

  View details for DOI 10.1021/acsnano.8b07738

  View details for Web of Science ID 000454567500005

• Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue (vol 9, 2740, 2018) NATURE COMMUNICATIONS Feig, V. R., Tran, H., Lee, M., Bao, Z. 2018; 9: 5030

  Abstract

  The original version of this Article contained an error in the second sentence of the 'Materials' section of the Methods, which incorrectly read 'PEDOT:PSS synthesized by Orgacon (739324 Aldrich, MDL MFCD07371079) was purchased as a surfactant-free aqueous dispersion with 1.1 wt% solid content.' The correct version replaces this sentence with 'PEDOT:PSS Orgacon ICP 1050 was provided by Agfa as a surfactant-free aqueous dispersion with 1.1 wt% solid content.' This has been corrected in both the PDF and HTML versions of the Article.

  View details for PubMedID 30470738

• Nanomaterials in Skin-Inspired Electronics: Toward Soft and Robust Skin-like Electronic Nanosystems. ACS nano Son, D., Bao, Z. 2018

  Abstract

  Skin-inspired wearable electronic/biomedical systems based on functional nanomaterials with exceptional electrical and mechanical properties have revolutionized wearable applications, such as portable Internet of Things, personalized healthcare monitors, human-machine interfaces, and even always-connected precise medicine systems. Despite these advancements, including the ability to predict and to control nanolevel phenomena of functional nanomaterials precisely and strategies for integrating nanomaterials onto desired substrates without performance losses, skin-inspired electronic nanosystems are not yet feasible beyond proof-of-concept devices. In this Perspective, we provide an outlook on skin-like electronics through the review of several recent reports on various materials strategies and integration methodologies of stretchable conducting and semiconducting nanomaterials, which are used as electrodes and active layers in stretchable sensors, transistors, multiplexed arrays, and integrated circuits. To overcome the challenge of realizing robust electronic nanosystems, we discuss using nanomaterials in dynamically cross-linked polymer matrices, focusing on the latest innovations in stretchable self-healing electronics, which could change the paradigm of wearable electronics.

  View details for PubMedID 30460841

• A hierarchically patterned, bioinspired e-skin able to detect the direction of applied pressure for robotics. Science robotics Boutry, C. M., Negre, M., Jorda, M., Vardoulis, O., Chortos, A., Khatib, O., Bao, Z. 2018; 3 (24)

  Abstract

  Tactile sensing is required for the dexterous manipulation of objects in robotic applications. In particular, the ability to measure and distinguish in real time normal and shear forces is crucial for slip detection and interaction with fragile objects. Here, we report a biomimetic soft electronic skin (e-skin) that is composed of an array of capacitors and capable of measuring and discriminating in real time both normal and tangential forces. It is enabled by a three-dimensional structure that mimics the interlocked dermis-epidermis interface in human skin. Moreover, pyramid microstructures arranged along nature-inspired phyllotaxis spirals resulted in an e-skin with increased sensitivity, minimal hysteresis, excellent cycling stability, and response time in the millisecond range. The e-skin provided sensing feedback for controlling a robot arm in various tasks, illustrating its potential application in robotics with tactile feedback.

  View details for DOI 10.1126/scirobotics.aau6914

  View details for PubMedID 33141713

• A hierarchically patterned, bioinspired e-skin able to detect the direction of applied pressure for robotics SCIENCE ROBOTICS Boutry, C. M., Negre, M., Jorda, M., Vardoulis, O., Chortos, A., Khatib, O., Bao, Z. 2018; 3 (24)

  View details for DOI 10.1126/scirobotics.aau6914

  View details for Web of Science ID 000450814400002

• Soft conductive micropillar electrode arrays for biologically relevant electrophysiological recording PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Liu, Y., McGuire, A. F., Lou, H., Li, T. L., Tok, J. H., Cui, B., Bao, Z. 2018; 115 (46): 11718–23

  View details for DOI 10.1073/pnas.1810827115

  View details for Web of Science ID 000449934400036

• Synthetic Routes for a 2D Semiconductive Copper Hexahydroxybenzene Metal-Organic Framework JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Park, J., Hinckley, A. C., Huang, Z., Feng, D., Yakoyenko, A. A., Lee, M., Chen, S., Zou, X., Bao, Z. 2018; 140 (44): 14533–37

  Abstract

  Conductive metal-organic frameworks (c-MOFs) have shown outstanding performance in energy storage and electrocatalysis. Varying the bridging metal species and the coordinating atom are versatile approaches to tune their intrinsic electronic properties in c-MOFs. Herein we report the first synthesis of the oxygen analog of M3(C6X6)2 (X = NH, S) family using Cu(II) and hexahydroxybenzene (HHB), namely Cu-HHB [Cu3(C6O6)2], through a kinetically controlled approach with a competing coordination reagent. We also successfully demonstrate an economical synthetic approach using tetrahydroxyquinone as the starting material. Cu-HHB was found to have a partially eclipsed packing between adjacent 2D layers and a bandgap of approximately 1 eV. The addition of Cu-HHB to the family of synthetically realized M3(C6X6)2 c-MOFs will enable greater understanding of the influence of the organic linkers and metals, and further broadens the range of applications for these materials.

  View details for PubMedID 30176142

• An integrated self-healable electronic skin system fabricated via dynamic reconstruction of a nanostructured conducting network NATURE NANOTECHNOLOGY Son, D., Kang, J., Vardoulis, O., Kim, Y., Matsuhisa, N., Oh, J., To, J. F., Mun, J., Katsumata, T., Liu, Y., McGuire, A. F., Krason, M., Molina-Lopez, F., Ham, J., Kraft, U., Lee, Y., Yun, Y., Tok, J., Bao, Z. 2018; 13 (11): 1057-+

  View details for DOI 10.1038/s41565-018-0244-6

  View details for Web of Science ID 000449291700020

• Stretchable organic optoelectronic sensorimotor synapse SCIENCE ADVANCES Lee, Y., Oh, J., Xu, W., Kim, O., Kim, T., Kang, J., Kim, Y., Son, D., Tok, J., Park, M., Bao, Z., Lee, T. 2018; 4 (11)

  View details for DOI 10.1126/sciadv.aat7387

  View details for Web of Science ID 000452212000019

• Stretchable organic optoelectronic sensorimotor synapse. Science advances Lee, Y., Oh, J. Y., Xu, W., Kim, O., Kim, T. R., Kang, J., Kim, Y., Son, D., Tok, J. B., Park, M. J., Bao, Z., Lee, T. 2018; 4 (11): eaat7387

  Abstract

  Emulation of human sensory and motor functions becomes a core technology in bioinspired electronics for next-generation electronic prosthetics and neurologically inspired robotics. An electronic synapse functionalized with an artificial sensory receptor and an artificial motor unit can be a fundamental element of bioinspired soft electronics. Here, we report an organic optoelectronic sensorimotor synapse that uses an organic optoelectronic synapse and a neuromuscular system based on a stretchable organic nanowire synaptic transistor (s-ONWST). The voltage pulses of a self-powered photodetector triggered by optical signals drive the s-ONWST, and resultant informative synaptic outputs are used not only for optical wireless communication of human-machine interfaces but also for light-interactive actuation of an artificial muscle actuator in the same way that a biological muscle fiber contracts. Our organic optoelectronic sensorimotor synapse suggests a promising strategy toward developing bioinspired soft electronics, neurologically inspired robotics, and electronic prostheses.

  View details for PubMedID 30480091

• A Dual-Crosslinking Design for Resilient Lithium-Ion Conductors ADVANCED MATERIALS Lopez, J., Sun, Y., Mackanic, D. G., Lee, M., Foudeh, A. M., Song, M., Cui, Y., Bao, Z. 2018; 30 (43)

  View details for DOI 10.1002/adma.201804142

  View details for Web of Science ID 000448786000025

• Effect of Nonconjugated Spacers on Mechanical Properties of Semiconducting Polymers for Stretchable Transistors ADVANCED FUNCTIONAL MATERIALS Mun, J., Wang, G., Oh, J., Katsumata, T., Lee, F. L., Kang, J., Wu, H., Lissel, F., Rondeau-Gagne, S., Tok, J., Bao, Z. 2018; 28 (43)

  View details for DOI 10.1002/adfm.201804222

  View details for Web of Science ID 000448258800011

• Enhanced Process Integration and Device Performance of Carbon Nanotubes via Flocculation SMALL METHODS Gao, T. Z., Lei, T., Molina-Lopez, F., Bao, Z. 2018; 2 (10)

  View details for DOI 10.1002/smtd.201800189

  View details for Web of Science ID 000446671200019

• Concentrated mixed cation acetate "water-in-salt" solutions as green and low-cost high voltage electrolytes for aqueous batteries ENERGY & ENVIRONMENTAL SCIENCE Lukatskaya, M. R., Feldblyum, J. I., Mackanic, D. G., Lissel, F., Michels, D. L., Cui, Y., Bao, Z. 2018; 11 (10): 2876–83

  View details for DOI 10.1039/c8ee00833g

  View details for Web of Science ID 000448339100011

• Effects of Polymer Coatings on Electrodeposited Lithium Metal JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lopez, J., Pei, A., Oh, J., Wang, G., Cui, Y., Bao, Z. 2018; 140 (37): 11735–44

  Abstract

  The electrodeposition of lithium metal is a key process in next-generation, high energy density storage devices. However, the high reactivity of the lithium metal causes short cycling lifetimes and dendrite growth that can pose a serious safety issue. Recently, a number of approaches have been pursued to stabilize the lithium metal-electrolyte interface, including soft polymeric coatings that have shown the ability to enable high-rate and high-capacity lithium metal cycling, but a clear understanding of how to design and modify these coatings has not yet been established. In this work, we studied the effects of several polymers with systematically varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition, we determine that the morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithium deposit size. Low surface energy polymers were found to promote larger deposits with smaller surface areas. This may be explained by a reduced interaction between the coating and the lithium surface and thus an increase in the interfacial energy. On the other hand, high dielectric constant polymers were found to increase the exchange current and gave larger lithium deposits due to the decreased overpotentials at a fixed current density. We also observed that the thickness of the polymer coating should be optimized for each individual polymer. Furthermore, polymer reactivity was found to strongly influence the Coulombic efficiency. Overall, this work offers new fundamental insights into lithium electrodeposition processes and provides direction for the design of new polymer coatings to better stabilize the lithium metal anode.

  View details for DOI 10.1021/jacs.8b06047

  View details for Web of Science ID 000445439700030

  View details for PubMedID 30152228

• A Dual-Crosslinking Design for Resilient Lithium-Ion Conductors. Advanced materials (Deerfield Beach, Fla.) Lopez, J., Sun, Y., Mackanic, D. G., Lee, M., Foudeh, A. M., Song, M., Cui, Y., Bao, Z. 2018: e1804142

  Abstract

  Solid-state electrolyte materials are attractive options for meeting the safety and performance needs of advanced lithium-based rechargeable battery technologies because of their improved mechanical and thermal stability compared to liquid electrolytes. However, there is typically a tradeoff between mechanical and electrochemical performance. Here an elastic Li-ion conductor with dual covalent and dynamic hydrogen bonding crosslinks is described to provide high mechanical resilience without sacrificing the room-temperature ionic conductivity. A solid-state lithium-metal/LiFePO4 cell with this resilient electrolyte can operate at room temperature with a high cathode capacity of 152 mAh g-1 for 300 cycles and can maintain operation even after being subjected to intense mechanical impact testing. This new dual crosslinking design provides robust mechanical properties while maintaining ionic conductivity similar to state-of-the-art polymer-based electrolytes. This approach opens a route toward stable, high-performance operation of solid-state batteries even under extreme abuse.

  View details for PubMedID 30199111

• Crosslinked Poly(tetrahydrofuran) as a Loosely Coordinating Polymer Electrolyte ADVANCED ENERGY MATERIALS Mackanic, D. G., Michaels, W., Lee, M., Feng, D., Lopez, J., Qin, J., Cui, Y., Bao, Z. 2018; 8 (25)

  View details for DOI 10.1002/aenm.201800703

  View details for Web of Science ID 000443674100005

• Enhanced Charge Transport and Stability Conferred by Iron(III)-Coordination in a Conjugated Polymer Thin-Film Transistors ADVANCED ELECTRONIC MATERIALS Wu, H., Rondeau-Gagne, S., Chiu, Y., Lissel, F., To, J. F., Tsao, Y., Oh, J., Tang, B., Chen, W., Tok, J., Bao, Z. 2018; 4 (9)

  View details for DOI 10.1002/aelm.201800239

  View details for Web of Science ID 000444071300018

• Electronic biosensing with flexible organic transistor devices FLEXIBLE AND PRINTED ELECTRONICS Kotlowski, C., Aspermair, P., Khan, H., Reiner-Rozman, C., Breu, J., Szunerits, S., Kim, J., Bao, Z., Kleber, C., Pelosi, P., Knoll, W. 2018; 3 (3)

  View details for DOI 10.1088/2058-8585/aad433

  View details for Web of Science ID 000444324500001

• An integrated self-healable electronic skin system fabricated via dynamic reconstruction of a nanostructured conducting network. Nature nanotechnology Son, D., Kang, J., Vardoulis, O., Kim, Y., Matsuhisa, N., Oh, J. Y., To, J. W., Mun, J., Katsumata, T., Liu, Y., McGuire, A. F., Krason, M., Molina-Lopez, F., Ham, J., Kraft, U., Lee, Y., Yun, Y., Tok, J. B., Bao, Z. 2018

  Abstract

  Electronic skin devices capable of monitoring physiological signals and displaying feedback information through closed-loop communication between the user and electronics are being considered for next-generation wearables and the 'Internet of Things'. Such devices need to be ultrathin to achieve seamless and conformal contact with the human body, to accommodate strains from repeated movement and to be comfortable to wear. Recently, self-healing chemistry has driven important advances in deformable and reconfigurable electronics, particularly with self-healable electrodes as the key enabler. Unlike polymer substrates with self-healable dynamic nature, the disrupted conducting network is unable to recover its stretchability after damage. Here, we report the observation of self-reconstruction of conducting nanostructures when in contact with a dynamically crosslinked polymer network. This, combined with the self-bonding property of self-healing polymer, allowed subsequent heterogeneous multi-component device integration of interconnects, sensors and light-emitting devices into a single multi-functional system. This first autonomous self-healable and stretchable multi-component electronic skin paves the way for future robust electronics.

  View details for PubMedID 30127474

• Dual-crosslinking design for resilient lithium ion conductor Lopez, J., Sun, Y., Cui, Y., Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104413

• Design of intrinsically stretchable polymer semiconductors Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104452

• High performance roll-to-roll printed PTB7-Th/PC71BM organic solar cells Gu, K., Gu, X., Zhou, Y., Yan, H., Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609105650

• Biodegradable and stretchable electronic materials for transient electronics Tran, H., Feig, V., Xu, J., Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104455

• Insights on the interaction of polymer coatings with electrodeposited lithium metal Lopez, J., Pei, A., Cui, Y., Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104232

• Understanding the influence of polymer properties on the stability of high capacity silicon and lithium metal anodes Lopez, J., Pei, A., Cui, Y., Bao, Z. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609104226

• An Elastic Autonomous Self-Healing Capacitive Sensor Based on a Dynamic Dual Crosslinked Chemical System ADVANCED MATERIALS Zhang, Q., Niu, S., Wang, L., Lopez, J., Chen, S., Cai, Y., Du, R., Liu, Y., Lai, J., Liu, L., Li, C., Yan, X., Liu, C., Tok, J., Jia, X., Bao, Z. 2018; 30 (33): e1801435

  Abstract

  Adopting self-healing, robust, and stretchable materials is a promising method to enable next-generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self-healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self-healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal-coordinated bonds (β-diketone-europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self-healing and exhibits excellent elasticity. The polymer network forms a microphase-separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self-healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self-healable dielectric layer is fabricated with a dual-dynamic bonding polymer system and self-healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self-healable touch pad.

  View details for PubMedID 29978512

• Stabilization of Hexaaminobenzene in a 2D Conductive Metal-Organic Framework for High Power Sodium Storage JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Park, J., Lee, M., Feng, D., Huang, Z., Hinckley, A. C., Yakoyenko, A., Zou, X., Cui, Y., Bao, Z. 2018; 140 (32): 10315–23

  Abstract

  Redox-active organic materials have gained growing attention as electrodes of rechargeable batteries. However, their key limitations are the low electronic conductivity and limited chemical and structural stability under redox conditions. Herein, we report a new cobalt-based 2D conductive metal-organic framework (MOF), Co-HAB, having stable, accessible, dense active sites for high-power energy storage device through conjugative coordination between a redox-active linker, hexaaminobenzene (HAB), and a Co(II) center. Given the exceptional capability of Co-HAB for stabilizing reactive HAB, a reversible three-electron redox reaction per HAB was successfully demonstrated for the first time, thereby presenting a promising new electrode material for sodium-ion storage. Specifically, through synthetic tunability of Co-HAB, the bulk electrical conductivity of 1.57 S cm-1 was achieved, enabling an extremely high rate capability, delivering 214 mAh g-1 within 7 min or 152 mAh g-1 in 45 s. Meanwhile, an almost linear increase of the areal capacity upon increasing active mass loading up to 9.6 mg cm-2 was obtained, demonstrating 2.6 mAh cm-2 with a trace amount of conducting agent.

  View details for DOI 10.1021/jacs.8b06020

  View details for Web of Science ID 000442183700037

  View details for PubMedID 30041519

• Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue. Nature communications Feig, V. R., Tran, H., Lee, M., Bao, Z. 2018; 9 (1): 2740

  Abstract

  Conductive and stretchable materials that match the elastic moduli of biological tissue (0.5-500kPa) are desired for enhanced interfacial and mechanical stability. Compared with inorganic and dry polymeric conductors, hydrogels made with conducting polymers are promising soft electrode materials due to their high water content. Nevertheless, most conducting polymer-based hydrogels sacrifice electronic performance to obtain usefulmechanical properties. Here we report a method that overcomes this limitation using two interpenetrating hydrogel networks, one of which is formed by the gelation of the conducting polymer PEDOT:PSS. Due to the connectivity of the PEDOT:PSS network, conductivities up to 23Sm-1 are achieved, a record for stretchable PEDOT:PSS-based hydrogels. Meanwhile, the low concentration of PEDOT:PSS enables orthogonal control over the composite mechanical properties using a secondary polymer network. We demonstrate tunability of the elastic modulus over three biologically relevant orders of magnitude without compromising stretchability (>100%) or conductivity (>10Sm-1).

  View details for PubMedID 30013027

• Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue NATURE COMMUNICATIONS Feig, V. R., Tran, H., Lee, M., Bao, Z. 2018; 9

  View details for DOI 10.1038/s41467-018-05222-4

  View details for Web of Science ID 000438683100013

• Nonhalogenated Solvent Processable and Printable High-Performance Polymer Semiconductor Enabled by Isomeric Nonconjugated Flexible Linkers MACROMOLECULES Wang, G., Molina-Lopez, F., Zhang, H., Xu, J., Wu, H., Lopez, J., Shaw, L., Mun, J., Zhang, Q., Wang, S., Ehrlich, A., Bao, Z. 2018; 51 (13): 4976–85

  View details for DOI 10.1021/acs.macromol.8b00971

  View details for Web of Science ID 000438654100023

• Enhancing Molecular Alignment and Charge Transport of Solution-Sheared Semiconducting Polymer Films by the Electrical-Blade Effect ADVANCED ELECTRONIC MATERIALS Molina-Lopez, F., Wu, H., Wang, G., Yan, H., Shaw, L., Xu, J., Toney, M. F., Bao, Z. 2018; 4 (7)

  View details for DOI 10.1002/aelm.201800110

  View details for Web of Science ID 000437828700015

• Designing Boron Nitride Islands in Carbon Materials for Efficient Electrochemical Synthesis of Hydrogen Peroxide. Journal of the American Chemical Society Chen, S., Chen, Z., Siahrostami, S., Higgins, D., Nordlund, D., Sokaras, D., Kim, T. R., Liu, Y., Yan, X., Nilsson, E., Sinclair, R., Norskov, J. K., Jaramillo, T. F., Bao, Z. 2018; 140 (25): 7851–59

  Abstract

  Heteroatom-doped carbons have drawn increasing research interest as catalysts for various electrochemical reactions due to their unique electronic and surface structures. In particular, co-doping of carbon with boron and nitrogen has been shown to provide significant catalytic activity for oxygen reduction reaction (ORR). However, limited experimental work has been done to systematically study these materials, and much remains to be understood about the nature of the active site(s), particularly with regards to the factors underlying the activity enhancements of these boron-carbon-nitrogen (BCN) materials. Herein, we prepare several BCN materials experimentally with a facile and controlled synthesis method, and systematically study their electrochemical performance. We demonstrate the existence of h-BN domains embedded in the graphitic structures of these materials using X-ray spectroscopy. These synthesized structures yield higher activity and selectivity toward the 2e- ORR to H2O2 than structures with individual B or N doping. We further employ density functional theory calculations to understand the role of a variety of h-BN domains within the carbon lattice for the ORR and find that the interface between h-BN domains and graphene exhibits unique catalytic behavior that can preferentially drive the production of H2O2. To the best of our knowledge, this is the first example of h-BN domains in carbon identified as a novel system for the electrochemical production of H2O2.

  View details for PubMedID 29874062

• Designing Boron Nitride Islands in Carbon Materials for Efficient Electrochemical Synthesis of Hydrogen Peroxide JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Chen, S., Chen, Z., Siahrostami, S., Higgins, D., Nordlund, D., Sokaras, D., Kim, T., Liu, Y., Yan, X., Nilsson, E., Sinclair, R., Norskov, J. K., Jaramillo, T. F., Bao, Z. 2018; 140 (25): 7851-7859

  View details for DOI 10.1021/jacs.8b02798

  View details for Web of Science ID 000436910300018

• Microstructural Evolution of the Thin Films of a Donor-Acceptor Semiconducting Polymer Deposited by Meniscus-Guided Coating MACROMOLECULES Shaw, L., Yan, H., Gu, X., Hayoz, P., Weitz, R., Kaelblein, D., Toney, M. F., Bao, Z. 2018; 51 (11): 4325–40

  View details for DOI 10.1021/acs.macromol.8b00350

  View details for Web of Science ID 000435417800042

• A bioinspired flexible organic artificial afferent nerve SCIENCE Kim, Y., Chortos, A., Xu, W., Liu, Y., Oh, J., Son, D., Kang, J., Foudeh, A. M., Zhu, C., Lee, Y., Niu, S., Liu, J., Pfattner, R., Bao, Z., Lee, T. 2018; 360 (6392): 998-+

  Abstract

  The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics.

  View details for PubMedID 29853682

• Ionically Conductive Self-Healing Binder for Low Cost Si Microparticles Anodes in Li-Ion Batteries ADVANCED ENERGY MATERIALS Munaoka, T., Yan, X., Lopez, J., To, J. F., Park, J., Tok, J., Cui, Y., Bao, Z. 2018; 8 (14)

  View details for DOI 10.1002/aenm.201703138

  View details for Web of Science ID 000435713600020

• Skin-Inspired Electronics: An Emerging Paradigm ACCOUNTS OF CHEMICAL RESEARCH Wang, S., Oh, J., Xu, J., Tran, H., Bao, Z. 2018; 51 (5): 1033–45

  Abstract

  Future electronics will take on more important roles in people's lives. They need to allow more intimate contact with human beings to enable advanced health monitoring, disease detection, medical therapies, and human-machine interfacing. However, current electronics are rigid, nondegradable and cannot self-repair, while the human body is soft, dynamic, stretchable, biodegradable, and self-healing. Therefore, it is critical to develop a new class of electronic materials that incorporate skinlike properties, including stretchability for conformable integration, minimal discomfort and suppressed invasive reactions; self-healing for long-term durability under harsh mechanical conditions; and biodegradability for reducing environmental impact and obviating the need for secondary device removal for medical implants. These demands have fueled the development of a new generation of electronic materials, primarily composed of polymers and polymer composites with both high electrical performance and skinlike properties, and consequently led to a new paradigm of electronics, termed "skin-inspired electronics". This Account covers recent important advances in skin-inspired electronics, from basic material developments to device components and proof-of-concept demonstrations for integrated bioelectronics applications. To date, stretchability has been the most prominent focus in this field. In contrast to strain-engineering approaches that extrinsically impart stretchability into inorganic electronics, intrinsically stretchable materials provide a direct route to achieve higher mechanical robustness, higher device density, and scalable fabrication. The key is the introduction of strain-dissipation mechanisms into the material design, which has been realized through molecular engineering (e.g., soft molecular segments, dynamic bonds) and physical engineering (e.g., nanoconfinement effect, geometric design). The material design concepts have led to the successful demonstrations of stretchable conductors, semiconductors, and dielectrics without sacrificing their electrical performance. Employing such materials, innovative device design coupled with fabrication method development has enabled stretchable sensors and displays as input/output components and large-scale transistor arrays for circuits and active matrixes. Strategies to incorporate self-healing into electronic materials are the second focus of this Account. To date, dynamic intermolecular interactions have been the most effective approach for imparting self-healing properties onto polymeric electronic materials, which have been utilized to fabricate self-healing sensors and actuators. Moreover, biodegradability has emerged as an important feature in skin-inspired electronics. The incorporation of degradable moieties along the polymer backbone allows for degradable conducting polymers and the use of bioderived materials has led to the demonstration of biodegradable functional devices, such as sensors and transistors. Finally, we highlight examples of skin-inspired electronics for three major applications: prosthetic e-skins, wearable electronics, and implantable electronics.

  View details for PubMedID 29693379

• Disentanglement of excited-state dynamics with implications for FRET measurements: two-dimensional electronic spectroscopy of a BODIPY-functionalized cavitand CHEMICAL SCIENCE Otto, J. P., Wang, L., Pochorovski, I., Blau, S. M., Aspuru-Guzik, A., Bao, Z., Engel, G. S., Chiu, M. 2018; 9 (15): 3694–3703

  Abstract

  Förster Resonance Energy Transfer (FRET) is the incoherent transfer of an electronic excitation from a donor fluorophore to a nearby acceptor. FRET has been applied as a probe of local chromophore environments and distances on the nanoscale by extrapolating transfer efficiencies from standard experimental parameters, such as fluorescence intensities or lifetimes. Competition from nonradiative relaxation processes is often assumed to be constant in these extrapolations, but in actuality, this competition depends on the donor and acceptor environments and can, therefore, be affected by conformational changes. To study the effects of nonradiative relaxation on FRET dynamics, we perform two-dimensional electronic spectroscopy (2DES) on a pair of azaboraindacene (BODIPY) dyes, attached to opposite arms of a resorcin[4]arene cavitand. Temperature-induced switching between two equilibrium conformations, vase at 294 K to kite at 193 K, increases the donor-acceptor distance from 0.5 nm to 3 nm, affecting both FRET efficiency and nonradiative relaxation. By disentangling different dynamics based on lifetimes extracted from a series of 2D spectra, we independently observe nonradiative relaxation, FRET, and residual fluorescence from the donor in both vase to kite conformations. We observe changes in both FRET rate and nonradiative relaxation when the molecule switches from vase to kite, and measure a significantly greater difference in transfer efficiency between conformations than would be determined by standard lifetime-based measurements. These observations show that changes in competing nonradiative processes must be taken into account when highly accurate measurements of FRET efficiency are desired.

  View details for PubMedID 29780500

  View details for PubMedCentralID PMC5935064

• Quadruple H-Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yan, X., Liu, Z., Zhang, Q., Lopez, J., Wang, H., Wu, H., Niu, S., Yan, H., Wang, S., Lei, T., Li, J., Qi, D., Huang, P., Huang, J., Zhang, Y., Wang, Y., Li, G., Tok, J., Chen, X., Bao, Z. 2018; 140 (15): 5280–89

  Abstract

  Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-1-3) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-2 was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m2), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics.

  View details for PubMedID 29595956

• Fred Wudl's fifty-year contribution to organic semiconductors JOURNAL OF MATERIALS CHEMISTRY C Zhang, Q., Perepichka, D. F., Bao, Z. 2018; 6 (14): 3483–84

  View details for DOI 10.1039/c8tc90055h

  View details for Web of Science ID 000429529800001

• Biodegradable Polymeric Materials in Degradable Electronic Devices ACS CENTRAL SCIENCE Feig, V. R., Tran, H., Bao, Z. 2018; 4 (3): 337–48

  Abstract

  Biodegradable electronics have great potential to reduce the environmental footprint of devices and enable advanced health monitoring and therapeutic technologies. Complex biodegradable electronics require biodegradable substrates, insulators, conductors, and semiconductors, all of which comprise the fundamental building blocks of devices. This review will survey recent trends in the strategies used to fabricate biodegradable forms of each of these components. Polymers that can disintegrate without full chemical breakdown (type I), as well as those that can be recycled into monomeric and oligomeric building blocks (type II), will be discussed. Type I degradation is typically achieved with engineering and material science based strategies, whereas type II degradation often requires deliberate synthetic approaches. Notably, unconventional degradable linkages capable of maintaining long-range conjugation have been relatively unexplored, yet may enable fully biodegradable conductors and semiconductors with uncompromised electrical properties. While substantial progress has been made in developing degradable device components, the electrical and mechanical properties of these materials must be improved before fully degradable complex electronics can be realized.

  View details for PubMedID 29632879

  View details for PubMedCentralID PMC5879474

• Tough and Water-Insensitive Self-Healing Elastomer for Robust Electronic Skin ADVANCED MATERIALS Kang, J., Son, D., Wang, G., Liu, Y., Lopez, J., Kim, Y., Oh, J., Katsumata, T., Mun, J., Lee, Y., Jin, L., Tok, J., Bao, Z. 2018; 30 (13): e1706846

  Abstract

  An electronic (e-) skin is expected to experience significant wear and tear over time. Therefore, self-healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e-skin. However, previously reported elastomers and especially self-healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch-insensitive high stretchability (1200%), high toughness of 12 000 J m-2 , and autonomous self-healing even in artificial sweat. The tough self-healing materials enable the wafer-scale fabrication of robust and stretchable self-healing e-skin devices, which will provide new directions for future soft robotics and skin prosthetics.

  View details for PubMedID 29424026

• Skin electronics from scalable fabrication of an intrinsically stretchable transistor array NATURE Wang, S., Xu, J., Wang, W., Wang, G., Rastak, R., Molina-Lopez, F., Chung, J., Niu, S., Feig, V. R., Lopez, J., Lei, T., Kwon, S., Kim, Y., Foudeh, A. M., Ehrlich, A., Gasperini, A., Yun, Y., Murmann, B., Tok, J., Bao, Z. 2018; 555 (7694): 83-+

  Abstract

  Skin-like electronics that can adhere seamlessly to human skin or within the body are highly desirable for applications such as health monitoring, medical treatment, medical implants and biological studies, and for technologies that include human-machine interfaces, soft robotics and augmented reality. Rendering such electronics soft and stretchable-like human skin-would make them more comfortable to wear, and, through increased contact area, would greatly enhance the fidelity of signals acquired from the skin. Structural engineering of rigid inorganic and organic devices has enabled circuit-level stretchability, but this requires sophisticated fabrication techniques and usually suffers from reduced densities of devices within an array. We reasoned that the desired parameters, such as higher mechanical deformability and robustness, improved skin compatibility and higher device density, could be provided by using intrinsically stretchable polymer materials instead. However, the production of intrinsically stretchable materials and devices is still largely in its infancy: such materials have been reported, but functional, intrinsically stretchable electronics have yet to be demonstrated owing to the lack of a scalable fabrication technology. Here we describe a fabrication process that enables high yield and uniformity from a variety of intrinsically stretchable electronic polymers. We demonstrate an intrinsically stretchable polymer transistor array with an unprecedented device density of 347 transistors per square centimetre. The transistors have an average charge-carrier mobility comparable to that of amorphous silicon, varying only slightly (within one order of magnitude) when subjected to 100 per cent strain for 1,000 cycles, without current-voltage hysteresis. Our transistor arrays thus constitute intrinsically stretchable skin electronics, and include an active matrix for sensory arrays, as well as analogue and digital circuit elements. Our process offers a general platform for incorporating other intrinsically stretchable polymer materials, enabling the fabrication of next-generation stretchable skin electronic devices.

  View details for PubMedID 29466334

• Microstructural origin of resistance-strain hysteresis in carbon nanotube thin film conductors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jin, L., Chortos, A., Lian, F., Pop, E., Linder, C., Bao, Z., Cai, W. 2018; 115 (9): 1986–91

  Abstract

  A basic need in stretchable electronics for wearable and biomedical technologies is conductors that maintain adequate conductivity under large deformation. This challenge can be met by a network of one-dimensional (1D) conductors, such as carbon nanotubes (CNTs) or silver nanowires, as a thin film on top of a stretchable substrate. The electrical resistance of CNT thin films exhibits a hysteretic dependence on strain under cyclic loading, although the microstructural origin of this strain dependence remains unclear. Through numerical simulations, analytic models, and experiments, we show that the hysteretic resistance evolution is governed by a microstructural parameter [Formula: see text] (the ratio of the mean projected CNT length over the film length) by showing that [Formula: see text] is hysteretic with strain and that the resistance is proportional to [Formula: see text] The findings are generally applicable to any stretchable thin film conductors consisting of 1D conductors with much lower resistance than the contact resistance in the high-density regime.

  View details for PubMedID 29440431

• Deformable Organic Nanowire Field-Effect Transistors ADVANCED MATERIALS Lee, Y., Oh, J., Kim, T., Gu, X., Kim, Y., Wang, G., Wu, H., Pfattner, R., To, J. F., Katsumata, T., Son, D., Kang, J., Matthews, J. R., Niu, W., He, M., Sinclair, R., Cui, Y., Tok, J., Lee, T., Bao, Z. 2018; 30 (7)

  View details for DOI 10.1002/adma.201704401

  View details for Web of Science ID 000424891900009

• The meniscus-guided deposition of semiconducting polymers NATURE COMMUNICATIONS Gu, X., Shaw, L., Gu, K., Toney, M. F., Bao, Z. 2018; 9: 534

  Abstract

  The electronic devices that play a vital role in our daily life are primarily based on silicon and are thus rigid, opaque, and relatively heavy. However, new electronics relying on polymer semiconductors are opening up new application spaces like stretchable and self-healing sensors and devices, and these can facilitate the integration of such devices into our homes, our clothing, and even our bodies. While there has been tremendous interest in such technologies, the widespread adoption of these organic electronics requires low-cost manufacturing techniques. Fortunately, the realization of organic electronics can take inspiration from a technology developed since the beginning of the Common Era: printing. This review addresses the critical issues and considerations in the printing methods for organic electronics, outlines the fundamental fluid mechanics, polymer physics, and deposition parameters involved in the fabrication process, and provides future research directions for the next generation of printed polymer electronics.

  View details for PubMedID 29416035

• Nanoscale Domain Imaging of All-Polymer Organic Solar Cells by Photo-Induced Force Microscopy ACS NANO Gu, K. L., Zhou, Y., Morrison, W. A., Park, K., Park, S., Bao, Z. 2018; 12 (2): 1473–81

  Abstract

  Rapid nanoscale imaging of the bulk heterojunction layer in organic solar cells is essential to the continued development of high-performance devices. Unfortunately, commonly used imaging techniques such as tunneling electron microscopy (TEM) and atomic force microscopy (AFM) suffer from significant drawbacks. For instance, assuming domain identity from phase contrast or topographical features can lead to inaccurate morphological conclusions. Here we demonstrate a technique known as photo-induced force microscopy (PiFM) for imaging organic solar cell bulk heterojunctions with nanoscale chemical specificity. PiFM is a relatively recent scanning probe microscopy technique that combines an AFM tip with a tunable infrared laser to induce a dipole for chemical imaging. Coupling the nanometer resolution of AFM with the chemical specificity of a tuned IR laser, we are able to spatially map the donor and acceptor domains in a model all-polymer bulk heterojunction with resolution approaching 10 nm. Domain size from PiFM images is compared to bulk-averaged results from resonant soft X-ray scattering, indicating excellent quantitative agreement. Further, we demonstrate that in our all-polymer system, the AFM topography, AFM phase, and PiFM show poor correlation, highlighting the need to move beyond standard AFM for morphology characterization of bulk heterojunctions.

  View details for PubMedID 29338202

• Deformable Organic Nanowire Field-Effect Transistors. Advanced materials (Deerfield Beach, Fla.) Lee, Y., Oh, J. Y., Kim, T. R., Gu, X., Kim, Y., Wang, G. N., Wu, H. C., Pfattner, R., To, J. W., Katsumata, T., Son, D., Kang, J., Matthews, J. R., Niu, W., He, M., Sinclair, R., Cui, Y., Tok, J. B., Lee, T. W., Bao, Z. 2018; 30 (7)

  Abstract

  Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next-generation implantable bioelectronic devices. Here, deformable field-effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high-molecular-weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field-effect mobility >8 cm2 V-1 s-1 with poly(vinylidenefluoride-co-trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine-like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min-1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.

  View details for DOI 10.1002/adma.201704401

  View details for PubMedID 29315845

• Stretchable Polymer Semiconductors for Plastic Electronics ADVANCED ELECTRONIC MATERIALS Wang, G., Gasperini, A., Bao, Z. 2018; 4 (2)

  View details for DOI 10.1002/aelm.201700429

  View details for Web of Science ID 000424888600010

• Understanding the Impact of Oligomeric Polystyrene Side Chain Arrangement on the All-Polymer Solar Cell Performance ADVANCED ENERGY MATERIALS Kurosawa, T., Gu, X., Gu, K. L., Zhou, Y., Yan, H., Wang, C., Wang, G., Toney, M. F., Bao, Z. 2018; 8 (2)

  View details for DOI 10.1002/aenm.201701552

  View details for Web of Science ID 000419864800009

• Analyzing the n-Doping Mechanism of an Air-Stable Small-Molecule Precursor ACS APPLIED MATERIALS & INTERFACES Schwarze, M., Naab, B. D., Tietze, M. L., Scholz, R., Pahner, P., Bussolotti, F., Kera, S., Kasemann, D., Bao, Z., Leo, K. 2018; 10 (1): 1340–46

  Abstract

  Efficient n-doping of organic semiconductors requires electron-donating molecules with small ionization energies, making such n-dopants usually sensitive to degradation under air exposure. A workaround consists in the usage of air-stable precursor molecules containing the actual n-doping species. Here, we systematically analyze the doping mechanism of the small-molecule precursor o-MeO-DMBI-Cl, which releases a highly reducing o-MeO-DMBI radical upon thermal evaporation. n-Doping of N,N-bis(fluoren-2-yl)-naphthalene tetracarboxylic diimide yields air-stable and highly conductive films suitable for application as electron transport layer in organic solar cells. By photoelectron spectroscopy, we determine a reduced doping efficiency at high doping concentrations. We attribute this reduction to a change of the precursor decomposition mechanism with rising crucible temperature, yielding an undesired demethylation at high evaporation rates. Our results do not only show the possibility of efficient and air-stable n-doping, but also support the design of novel air-stable precursor molecules of strong n-dopants.

  View details for PubMedID 29236472

• Compact Modeling of Carbon Nanotube Thin Film Transistors for Flexible Circuit Design Shao, L., Huang, T., Lei, T., Bao, Z., Beausolei, R., Cheng, K., IEEE IEEE. 2018: 491–96

  View details for Web of Science ID 000435148800089

• Roadmap on semiconductor-cell biointerfaces. Physical biology Tian, B., Xu, S., Rogers, J. A., Cestellos-Blanco, S., Yang, P., Carvalho-de-Souza, J. L., Bezanilla, F., Liu, J., Bao, Z., Hjort, M., Cao, Y., Melosh, N., Lanzani, G., Benfenati, F., Galli, G., Gygi, F., Kautz, R., Gorodetsky, A. A., Kim, S. S., Lu, T. K., Anikeeva, P., Cifra, M., Krivosudsky, O., Havelka, D., Jiang, Y. 2018; 15 (3): 031002

  Abstract

  This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world.

  View details for DOI 10.1088/1478-3975/aa9f34

  View details for PubMedID 29205173

• Soft conductive micropillar electrode arrays for biologically relevant electrophysiological recording. Proceedings of the National Academy of Sciences of the United States of America Liu, Y. n., McGuire, A. F., Lou, H. Y., Li, T. L., Tok, J. B., Cui, B. n., Bao, Z. n. 2018

  Abstract

  Multielectrode arrays (MEAs) are essential tools in neural and cardiac research as they provide a means for noninvasive, multiplexed recording of extracellular field potentials with high temporal resolution. To date, the mechanical properties of the electrode material, e.g., its Young's modulus, have not been taken into consideration in most MEA designs leaving hard materials as the default choice due to their established fabrication processes. However, the cell-electrode interface is known to significantly affect some aspects of the cell's behavior. In this paper, we describe the fabrication of a soft 3D micropillar electrode array. Using this array, we proceed to successfully record action potentials from monolayer cell cultures. Specifically, our conductive hydrogel micropillar electrode showed improved signal amplitude and signal-to-noise ratio, compared with conventional hard iridium oxide micropillar electrodes of the same diameter. Taken together, our fabricated soft micropillar electrode array will provide a tissue-like Young's modulus and thus a relevant mechanical microenvironment to fundamental cardiac and neural studies.

  View details for PubMedID 30377271

• Process Design Kit for Flexible Hybrid Electronics Shao, L., Huang, T., Lei, T., Bao, Z., Beausoleil, R., Cheng, K., ACM ASSOC COMPUTING MACHINERY. 2018: 651–57

  View details for Web of Science ID 000475955100123

• Defective Carbon-Based Materials for the Electrochemical Synthesis of Hydrogen Peroxide ACS SUSTAINABLE CHEMISTRY & ENGINEERING Chen, S., Chen, Z., Siahrostami, S., Kim, T., Nordlund, D., Sokaras, D., Nowak, S., To, J. F., Higgins, D., Sinclair, R., Norskov, J. K., Jaramillo, T. F., Bao, Z. 2018; 6 (1): 311–17

  View details for DOI 10.1021/acssuschemeng.7b02517

  View details for Web of Science ID 000419536800034

• Process Design Kit for Flexible Hybrid Electronics Shao, L., Huang, T., Lei, T., Bao, Z., Beausoleil, R., Cheng, K., IEEE IEEE. 2018: 651–57

  View details for Web of Science ID 000426987100122

• On the Working Mechanisms of Solid-State Double-Layer-Dielectric-Based Organic Field-Effect Transistors and Their Implication for Sensors ADVANCED ELECTRONIC MATERIALS Pfattner, R., Foudeh, A. M., Liong, C., Bettinson, L., Hinckley, A. C., Kong, D., Bao, Z. 2018; 4 (1)

  View details for DOI 10.1002/aelm.201700326

  View details for Web of Science ID 000419670400008

• Robust and conductive two-dimensional metal-organic frameworks with exceptionally high volumetric and areal capacitance NATURE ENERGY Feng, D., Lei, T., Lukatskaya, M. R., Park, J., Huang, Z., Lee, M., Shaw, L., Chen, S., Yakovenko, A. A., Kulkarni, A., Xiao, J., Fredrickson, K., Tok, J. B., Zou, X., Cui, Y., Bao, Z. 2018; 3 (1): 30–36

  View details for DOI 10.1038/s41560-017-0044-5

  View details for Web of Science ID 000419976100011

• Solution-Phase Conformation and Dynamics of Conjugated Isoindigo-Based Donor-Acceptor Polymer Single Chains JOURNAL OF PHYSICAL CHEMISTRY LETTERS Lee, F. L., Farimani, A., Gu, K. L., Yan, H., Toney, M. F., Bao, Z., Pande, V. S. 2017; 8 (22): 5479–86

  Abstract

  Conjugated polymers are the key material in thin-film organic optoelectronic devices due to the versatility of these molecules combined with their semiconducting properties. A molecular-scale understanding of conjugated polymers is important to the optimization of the thin-film morphology. We examine the solution-phase behavior of conjugated isoindigo-based donor-acceptor polymer single chains of various chain lengths using atomistic molecular dynamics simulations. Our simulations elucidate the transition from a rod-like to a coil-like conformation from an analysis of normal modes and persistence length. In addition, we find another transition based on the solvent environment, contrasting the coil-like conformation in a good solvent with a globule-like conformation in a poor solvent. Overall, our results provide valuable insights into the transition between conformational regimes for conjugated polymers as a function of both the chain length and the solvent environment, which will help to accurately parametrize higher level models.

  View details for PubMedID 29065685

• Stretchable Lithium-Ion Batteries Enabled by Device-Scaled Wavy Structure and Elastic-Sticky Separator ADVANCED ENERGY MATERIALS Liu, W., Chen, J., Chen, Z., Liu, K., Zhou, G., Sun, Y., Song, M., Bao, Z., Cui, Y. 2017; 7 (21)

  View details for DOI 10.1002/aenm.201701076

  View details for Web of Science ID 000414711100018

• High-performance sodium-organic battery by realizing four-sodium storage in disodium rhodizonate NATURE ENERGY Lee, M., Hong, J., Lopez, J., Sun, Y., Feng, D., Lim, K., Chueh, W. C., Toney, M. F., Cui, Y., Bao, Z. 2017; 2 (11)

  View details for DOI 10.1038/s41560-017-0014-y

  View details for Web of Science ID 000418243200002

• Enhanced Cycling Stability of Sulfur Electrodes through Effective Binding of Pyridine-Functionalized Polymer ACS ENERGY LETTERS Tsao, Y., Chen, Z., Rondeau-Gagne, S., Zhang, Q., Yao, H., Chen, S., Zhou, G., Zu, C., Cui, Y., Bao, Z. 2017; 2 (10): 2454–62

  View details for DOI 10.1021/acsenergylett.7b00772

  View details for Web of Science ID 000415914200040

• The Effects of Counter Anions on the Dynamic Mechanical Response in Polymer Networks Crosslinked by Metal-Ligand Coordination JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Rao, Y., Feig, V., Gu, X., Wang, G., Bao, Z. 2017; 55 (18): 3110–16

  View details for DOI 10.1002/pola.28675

  View details for Web of Science ID 000406937100029

• Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains ADVANCED FUNCTIONAL MATERIALS Schroeder, B. C., Kurosawa, T., Fu, T., Chiu, Y., Mun, J., Wang, G., Gu, X., Shaw, L., Kneller, J. E., Kreouzis, T., Toney, M. F., Bao, Z. 2017; 27 (34)

  View details for DOI 10.1002/adfm.201701973

  View details for Web of Science ID 000410162200010

• Reducing the contact resistance in bottom-contact-type organic field-effect transitors using an AgOx interface layer APPLIED PHYSICS EXPRESS Minagawa, M., Kim, Y., Claus, M., Bao, Z. 2017; 10 (9)

  View details for DOI 10.7567/APEX.10.091601

  View details for Web of Science ID 000408773900001

• Tunable electronic properties in a 2D metal-organic framework platform Park, J., Feng, D., Bao, Z. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000429556700389

• Roll-to-Roll Printed Large-Area All-Polymer Solar Cells with 5% Efficiency Based on a Low Crystallinity Conjugated Polymer Blend ADVANCED ENERGY MATERIALS Gu, X., Zhou, Y., Gu, K., Kurosawa, T., Guo, Y., Li, Y., Lin, H., Schroeder, B. C., Yan, H., Molina-Lopez, F., Tassone, C. J., Wang, C., Mannsfeld, S. B., Yan, H., Zhao, D., Toney, M. F., Bao, Z. 2017; 7 (14)

  View details for DOI 10.1002/aenm.201602742

  View details for Web of Science ID 000405839400019

• Universal Selective Dispersion of Semiconducting Carbon Nanotubes from Commercial Sources Using a Supramolecular Polymer. ACS nano Chortos, A., Pochorovski, I., Lin, P., Pitner, G., Yan, X., Gao, T. Z., To, J. W., Lei, T., Will, J. W., Wong, H. P., Bao, Z. 2017

  Abstract

  Selective extraction of semiconducting carbon nanotubes is a key step in the production of high-performance, solution-processed electronics. Here, we describe the ability of a supramolecular sorting polymer to selectively disperse semiconducting carbon nanotubes from five commercial sources with diameters ranging from 0.7 to 2.2 nm. The sorting purity of the largest-diameter nanotubes (1.4 to 2.2 nm; from Tuball) was confirmed by short channel measurements to be 97.5%. Removing the sorting polymer by acid-induced disassembly increased the transistor mobility by 94 and 24% for medium-diameter and large-diameter carbon nanotubes, respectively. Among the tested single-walled nanotube sources, the highest transistor performance of 61 cm(2)/V·s and on/off ratio >10(4) were realized with arc discharge carbon nanotubes with a diameter range from 1.2 to 1.7 nm. The length and quality of nanotubes sorted from different sources is compared using measurements from atomic force microscopy and Raman spectroscopy. The transistor mobility is found to correlate with the G/D ratio extracted from the Raman spectra.

  View details for DOI 10.1021/acsnano.7b01076

  View details for PubMedID 28528552

• Biocompatible and totally disintegrable semiconducting polymer for ultrathin and ultralightweight transient electronics PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Lei, T., Guan, M., Liu, J., Lin, H., Pfattner, R., Shaw, L., McGuire, A. F., Huang, T., Shao, L., Cheng, K., Tok, J. B., Bao, Z. 2017; 114 (20): 5107-5112

  Abstract

  Increasing performance demands and shorter use lifetimes of consumer electronics have resulted in the rapid growth of electronic waste. Currently, consumer electronics are typically made with nondecomposable, nonbiocompatible, and sometimes even toxic materials, leading to serious ecological challenges worldwide. Here, we report an example of totally disintegrable and biocompatible semiconducting polymers for thin-film transistors. The polymer consists of reversible imine bonds and building blocks that can be easily decomposed under mild acidic conditions. In addition, an ultrathin (800-nm) biodegradable cellulose substrate with high chemical and thermal stability is developed. Coupled with iron electrodes, we have successfully fabricated fully disintegrable and biocompatible polymer transistors. Furthermore, disintegrable and biocompatible pseudo-complementary metal-oxide-semiconductor (CMOS) flexible circuits are demonstrated. These flexible circuits are ultrathin (<1 μm) and ultralightweight (∼2 g/m(2)) with low operating voltage (4 V), yielding potential applications of these disintegrable semiconducting polymers in low-cost, biocompatible, and ultralightweight transient electronics.

  View details for DOI 10.1073/pnas.1701478114

  View details for Web of Science ID 000401314700044

  View details for PubMedID 28461459

• Lithium Metal Anodes with an Adaptive "Solid-Liquid" Interfacial Protective Layer JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, K., Pei, A., Lee, H. R., Kong, B., Liu, N., Lin, D., Liu, Y., Liu, C., Hsu, P., Bao, Z., Cui, Y. 2017; 139 (13): 4815-4820

  Abstract

  Lithium metal is an attractive anode for the next generation of high energy density lithium-ion batteries due to its high specific capacity (3,860 mAh g(-1)) and lowest overall anode potential. However, the key issue is that the static solid electrolyte interphase cannot match the dynamic volume changes of the Li anode, resulting in side reactions, dendrite growth, and poor electrodeposition behavior, which prevent its practical applications. Here, we show that the "solid-liquid" hybrid behavior of a dynamically cross-linked polymer enables its use as an excellent adaptive interfacial layer for Li metal anodes. The dynamic polymer can reversibly switch between its "liquid" and "solid" properties in response to the rate of lithium growth to provide uniform surface coverage and dendrite suppression, respectively, thereby enabling the stable operation of lithium metal electrodes. We believe that this example of engineering an adaptive Li/electrolyte interface brings about a new and promising way to address the intrinsic problems of lithium metal anodes.

  View details for DOI 10.1021/jacs.6b13314

  View details for Web of Science ID 000398764000034

  View details for PubMedID 28303712

• All-solution-processed stretchable transistor arrays based on polymer semiconductor and dielectric Wang, S., Lopez, F., Xu, J., Liu, J., Chung, J., Bao, Z. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569107451

• Degradable and biocompatible conjugated polymer for solution-processed imperceptible transient electronics Lei, T., Bao, Z. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569106849

• Separation of Semiconducting Carbon Nanotubes for Flexible and Stretchable Electronics Using Polymer Removable Method ACCOUNTS OF CHEMICAL RESEARCH Lei, T., Pochorovski, I., Bao, Z. 2017; 50 (4): 1096-1104

  Abstract

  Electronics that are soft, conformal, and stretchable are highly desirable for wearable electronics, prosthetics, and robotics. Among the various available electronic materials, single walled carbon nanotubes (SWNTs) and their network have exhibited high mechanical flexibility and stretchability, along with comparable electrical performance to traditional rigid materials, e.g. polysilicon and metal oxides. Unfortunately, SWNTs produced en masse contain a mixture of semiconducting (s-) and metallic (m-) SWNTs, rendering them unsuitable for electronic applications. Moreover, the poor solubility of SWNTs requires the introduction of insulating surfactants to properly disperse them into individual tubes for device fabrication. Compared to other SWNT dispersion and separation methods, e.g., DNA wrapping, density gradient ultracentrifugation, and gel chromatography, polymer wrapping can selectively disperse s-SWNTs with high selectivity (>99.7%), high concentration (>0.1 mg/mL), and high yield (>20%). In addition, this method only requires simple sonication and centrifuge equipment with short processing time down to 1 h. Despite these advantages, the polymer wrapping method still faces two major issues: (i) The purified s-SWNTs usually retain a substantial amount of polymers on their surface even after thorough rinsing. The low conductivity of the residual polymers impedes the charge transport in SWNT networks. (ii) Conjugated polymers used for SWNT wrapping are expensive. Their prices ($100-1000/g) are comparable or even higher than those of SWNTs ($10-300/g). These utilized conjugated polymers represent a large portion of the overall separation cost. In this Account, we summarize recent progresses in polymer design for selective dispersion and separation of SWNTs. We focus particularly on removable and/or recyclable polymers that enable low-cost and scalable separation methods. First, different separation methods are compared to show the advantages of the polymer wrapping methods. In specific, we compare different characterization methods used for purity evaluation. For s-SWNTs with high purity, i.e., >99%, short-channel (smaller than SWNT length) electrical measurement is more reliable than optical methods. Second, possible sorting mechanism and molecular design strategies are discussed. Polymer parameters such as backbone design and side chain engineering affect the polymer-SWNT interactions, leading to different dispersion concentration and selectivity. To address the above-mentioned limiting factors in both polymer contamination and cost issues, we describe two important polymer removal and cycling approaches: (i) changing polymer wrapping conformation to release SWNTs; (ii) depolymerization of conjugated polymer into small molecular units that have less affinity toward SWNTs. These methods allow the removal and recycling of the wrapping polymers, thus providing low-cost and clean s-SWNTs. Third, we discuss various applications of polymer-sorted s-SWNTs, including flexible/stretchable thin-film transistors, thermoelectric devices, and solar cells. In these applications, polymer-sorted s-SWNTs and their networks have exhibited good processability, attractive mechanical properties, and high electrical performance. An increasing number of studies have shown that the removable polymer approaches can completely remove polymer residues in SWNT networks and lead to enhanced charge carrier mobility, higher conductivity, and better heterojunction interface.

  View details for DOI 10.1021/acs.accounts.7b00062

  View details for Web of Science ID 000399859800047

  View details for PubMedID 28358486

• Development of a reactor with carbon catalysts for modular-scale, low-cost electrochemical generation of H2O2 REACTION CHEMISTRY & ENGINEERING Chen, Z., Chen, S., Siahrostami, S., Chakthranont, P., Hahn, C., Nordlund, D., Dimosthenis, S., Norskov, J. K., Bao, Z., Jaramillo, T. F. 2017; 2 (2): 239–45

  View details for DOI 10.1039/c6re00195e

  View details for Web of Science ID 000403324600016

• High-performance oxygen reduction and evolution carbon catalysis: From mechanistic studies to device integration NANO RESEARCH To, J. W., Ng, J. W., Siahrostami, S., Koh, A. L., Lee, Y., Chen, Z., Fong, K. D., Chen, S., He, J., Bae, W., Wilcox, J., Jeong, H. Y., Kim, K., Studt, F., Norskov, J. K., Jaramillo, T. F., Bao, Z. 2017; 10 (4): 1163-1177

  View details for DOI 10.1007/s12274-016-1347-8

  View details for Web of Science ID 000398382300005

• Chemical Vapor-Deposited Hexagonal Boron Nitride as a Scalable Template for High-Performance Organic Field-Effect Transistors CHEMISTRY OF MATERIALS Lee, T. H., Kim, K., Kim, G., Park, H. J., Scullion, D., Shaw, L., Kim, M., Gu, X., Bae, W., Santos, E. J., Lee, Z., Shin, H. S., Nishi, Y., Bao, Z. 2017; 29 (5): 2341-2347

  View details for DOI 10.1021/acs.chemmater.6b05517

  View details for Web of Science ID 000396639400049

• A highly stretchable, transparent, and conductive polymer. Science advances Wang, Y., Zhu, C., Pfattner, R., Yan, H., Jin, L., Chen, S., Molina-Lopez, F., Lissel, F., Liu, J., Rabiah, N. I., Chen, Z., Chung, J. W., Linder, C., Toney, M. F., Murmann, B., Bao, Z. 2017; 3 (3)

  Abstract

  Previous breakthroughs in stretchable electronics stem from strain engineering and nanocomposite approaches. Routes toward intrinsically stretchable molecular materials remain scarce but, if successful, will enable simpler fabrication processes, such as direct printing and coating, mechanically robust devices, and more intimate contact with objects. We report a highly stretchable conducting polymer, realized with a range of enhancers that serve a dual function: (i) they change morphology and (ii) they act as conductivity-enhancing dopants in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The polymer films exhibit conductivities comparable to the best reported values for PEDOT:PSS, with over 3100 S/cm under 0% strain and over 4100 S/cm under 100% strain-among the highest for reported stretchable conductors. It is highly durable under cyclic loading, with the conductivity maintained at 3600 S/cm even after 1000 cycles to 100% strain. The conductivity remained above 100 S/cm under 600% strain, with a fracture strain of 800%, which is superior to even the best silver nanowire- or carbon nanotube-based stretchable conductor films. The combination of excellent electrical and mechanical properties allowed it to serve as interconnects for field-effect transistor arrays with a device density that is five times higher than typical lithographically patterned wavy interconnects.

  View details for DOI 10.1126/sciadv.1602076

  View details for PubMedID 28345040

• n-Type Doped Conjugated Polymer for Nonvolatile Memory. Advanced materials Lee, W., Wu, H., Lu, C., Naab, B. D., Chen, W., Bao, Z. 2017

  Abstract

  This study demonstrates a facile way to efficiently induce strong memory behavior from common p-type conjugated polymers by adding n-type dopant 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole. The n-type doped p-channel conjugated polymers not only enhance n-type charge transport characteristics of the polymers, but also facilitate to storage charges and cause reversible bistable (ON and OFF states) switching upon application of gate bias. The n-type doped memory shows a large memory window of up to 47 V with an on/off current ratio larger than 10 000. The charge retention time can maintain over 100 000 s. Similar memory behaviors are also observed in other common semiconducting polymers such as poly(3-hexyl thiophene) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene], and a high mobility donor-acceptor polymer, poly(isoindigo-bithiophene). In summary, these observations suggest that this approach is a general method to induce memory behavior in conjugated polymers. To the best of the knowledge, this is the first report for p-type polymer memory achieved using n-type charge-transfer doping.

  View details for DOI 10.1002/adma.201605166

  View details for PubMedID 28234405

• Electric Field Tuning Molecular Packing and Electrical Properties of Solution-Shearing Coated Organic Semiconducting Thin Films ADVANCED FUNCTIONAL MATERIALS Molina-Lopez, F., Yan, H., Gu, X., Kim, Y., Toney, M. F., Bao, Z. 2017; 27 (8)

  View details for DOI 10.1002/adfm.201605503

  View details for Web of Science ID 000394683400008

• Electric Field Tuning Molecular Packing and Electrical Properties of Solution-Shearing Coated Organic Semiconducting Thin Films ADVANCED FUNCTIONAL MATERIALS Molina-Lopez, F., Yan, H., Gu, X., Kim, Y., Toney, M. F., Bao, Z. 2017; 27 (8)

  View details for DOI 10.1002/adfm.201605503

  View details for Web of Science ID 000394683400009

• Effects of Molecular Structure and Packing Order on the Stretchability of Semicrystalline Conjugated Poly(Tetrathienoacene-diketopyrrolopyrrole) Polymers ADVANCED ELECTRONIC MATERIALS Lu, C., Lee, W., Gu, X., Xu, J., Chou, H., Yan, H., Chiu, Y., He, M., Matthews, J. R., Niu, W., Tok, J. B., Toney, M. F., Chen, W., Bao, Z. 2017; 3 (2)

  View details for DOI 10.1002/aelm.201600311

  View details for Web of Science ID 000394901900002

• Stretchable and ultraflexible organic electronics MRS BULLETIN Lipomi, D. J., Bao, Z. 2017; 42 (2): 93-97

  View details for DOI 10.1557/mrs.2016.325

  View details for Web of Science ID 000398471500008

• Highly stretchable polymer semiconductor films through the nanoconfinement effect SCIENCE Xu, J., Wang, S., Wang, G. N., Zhu, C., Luo, S., Jin, L., Gu, X., Chen, S., Feig, V. R., To, J. W., Rondeau-Gagne, S., Park, J., Schroeder, B. C., Lu, C., Oh, J. Y., Wang, Y., Kim, Y., Yan, H., Sinclair, R., Zhou, D., Xue, G., Murmann, B., Linder, C., Cai, W., Tok, J. B., Chung, J. W., Bao, Z. 2017; 355 (6320): 59-?

  Abstract

  Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.

  View details for DOI 10.1126/science.aah4496

  View details for PubMedID 28059762

• Robust Design and Design Automation for Flexible Hybrid Electronics Huang, T., Shao, L., Lei, T., Beausoleil, R., Bao, Z., Cheng, K., IEEE IEEE. 2017

  View details for Web of Science ID 000424890101177

• Ultratransparent and stretchable graphene electrodes. Science advances Liu, N. n., Chortos, A. n., Lei, T. n., Jin, L. n., Kim, T. R., Bae, W. G., Zhu, C. n., Wang, S. n., Pfattner, R. n., Chen, X. n., Sinclair, R. n., Bao, Z. n. 2017; 3 (9): e1700159

  Abstract

  Two-dimensional materials, such as graphene, are attractive for both conventional semiconductor applications and nascent applications in flexible electronics. However, the high tensile strength of graphene results in fracturing at low strain, making it challenging to take advantage of its extraordinary electronic properties in stretchable electronics. To enable excellent strain-dependent performance of transparent graphene conductors, we created graphene nanoscrolls in between stacked graphene layers, referred to as multilayer graphene/graphene scrolls (MGGs). Under strain, some scrolls bridged the fragmented domains of graphene to maintain a percolating network that enabled excellent conductivity at high strains. Trilayer MGGs supported on elastomers retained 65% of their original conductance at 100% strain, which is perpendicular to the direction of current flow, whereas trilayer films of graphene without nanoscrolls retained only 25% of their starting conductance. A stretchable all-carbon transistor fabricated using MGGs as electrodes exhibited a transmittance of >90% and retained 60% of its original current output at 120% strain (parallel to the direction of charge transport). These highly stretchable and transparent all-carbon transistors could enable sophisticated stretchable optoelectronics.

  View details for PubMedID 28913422

• Investigating Limiting Factors in Stretchable All-Carbon Transistors for Reliable Stretchable Electronics. ACS nano Chortos, A. n., Zhu, C. n., Oh, J. Y., Yan, X. n., Pochorovski, I. n., To, J. W., Liu, N. n., Kraft, U. n., Murmann, B. n., Bao, Z. n. 2017; 11 (8): 7925–37

  Abstract

  Stretchable form factors enable electronic devices to conform to irregular 3D structures, including soft and moving entities. Intrinsically stretchable devices have potential advantages of high surface coverage of active devices, improved durability, and reduced processing costs. This work describes intrinsically stretchable transistors composed of single-walled carbon nanotube (SWNT) electrodes and semiconductors and a dielectric that consists of a nonpolar elastomer. The use of a nonpolar elastomer dielectric enabled hysteresis-free device characteristics. Compared to devices on SiO2 dielectrics, stretchable devices with nonpolar dielectrics showed lower mobility in ambient conditions because of the absence of doping from water. The effect of a SWNT band gap on device characteristics was investigated by using different SWNT sources as the semiconductor. Large-band-gap SWNTs exhibited trap-limited behavior caused by the low capacitance of the dielectric. In contrast, high-current devices based on SWNTs with smaller band gaps were more limited by contact resistance. Of the tested SWNT sources, SWNTs with a maximum diameter of 1.5 nm performed the best, with a mobility of 15.4 cm2/Vs and an on/off ratio >103 for stretchable transistors. Large-band-gap devices showed increased sensitivity to strain because of a pronounced dependence on the dielectric thickness, whereas contact-limited devices showed substantially less strain dependence.

  View details for PubMedID 28745872

• Bring on the bodyNET. Nature Chu, B. n., Burnett, W. n., Chung, J. W., Bao, Z. n. 2017; 549 (7672): 328–30

  View details for PubMedID 28933443

• Surface Fluorination of Reactive Battery Anode Materials for Enhanced Stability. Journal of the American Chemical Society Zhao, J. n., Liao, L. n., Shi, F. n., Lei, T. n., Chen, G. n., Pei, A. n., Sun, J. n., Yan, K. n., Zhou, G. n., Xie, J. n., Liu, C. n., Li, Y. n., Liang, Z. n., Bao, Z. n., Cui, Y. n. 2017; 139 (33): 11550–58

  Abstract

  Significant increases in the energy density of batteries must be achieved by exploring new materials and cell configurations. Lithium metal and lithiated silicon are two promising high-capacity anode materials. Unfortunately, both of these anodes require a reliable passivating layer to survive the serious environmental corrosion during handling and cycling. Here we developed a surface fluorination process to form a homogeneous and dense LiF coating on reactive anode materials, with in situ generated fluorine gas, by using a fluoropolymer, CYTOP, as the precursor. The process is effectively a "reaction in the beaker", avoiding direct handling of highly toxic fluorine gas. For lithium metal, this LiF coating serves as a chemically stable and mechanically strong interphase, which minimizes the corrosion reaction with carbonate electrolytes and suppresses dendrite formation, enabling dendrite-free and stable cycling over 300 cycles with current densities up to 5 mA/cm2. Lithiated silicon can serve as either a pre-lithiation additive for existing lithium-ion batteries or a replacement for lithium metal in Li-O2 and Li-S batteries. However, lithiated silicon reacts vigorously with the standard slurry solvent N-methyl-2-pyrrolidinone (NMP), indicating it is not compatible with the real battery fabrication process. With the protection of crystalline and dense LiF coating, LixSi can be processed in anhydrous NMP with a high capacity of 2504 mAh/g. With low solubility of LiF in water, this protection layer also allows LixSi to be stable in humid air (∼40% relative humidity). Therefore, this facile surface fluorination process brings huge benefit to both the existing lithium-ion batteries and next-generation lithium metal batteries.

  View details for PubMedID 28743184

• Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing ORGANIC ELECTRONICS Gu, K. L., Zhou, Y., Gu, X., Yan, H., Diao, Y., Kurosawa, T., Ganapathysubramanian, B., Toney, M. E., Bao, Z. 2017; 40: 79-87

  View details for DOI 10.1016/j.orgel.2016.10.033

  View details for Web of Science ID 000390585800012

• Characterization and Understanding of Thermoresponsive Polymer Composites Based on Spiky Nanostructured Fillers ADVANCED ELECTRONIC MATERIALS Chen, Z., Pfattner, R., Bao, Z. 2017; 3 (1)

  View details for DOI 10.1002/aelm.201600397

  View details for Web of Science ID 000393670800015

• Trade-Off between Trap Filling, Trap Creation, and Charge Recombination Results in Performance Increase at Ultralow Doping Levels in Bulk Heterojunction Solar Cells ADVANCED ENERGY MATERIALS Shang, Z., Heumueller, T., Prasanna, R., Burkhard, G. F., Naab, B. D., Bao, Z., McGehee, M. D., Salleo, A. 2016; 6 (24)

  View details for DOI 10.1002/aenm.201601149

  View details for Web of Science ID 000396320500008

• The rise of plastic bioelectronics NATURE Someya, T., Bao, Z., Malliaras, G. G. 2016; 540 (7633): 379-385

  Abstract

  Plastic bioelectronics is a research field that takes advantage of the inherent properties of polymers and soft organic electronics for applications at the interface of biology and electronics. The resulting electronic materials and devices are soft, stretchable and mechanically conformable, which are important qualities for interacting with biological systems in both wearable and implantable devices. Work is currently aimed at improving these devices with a view to making the electronic-biological interface as seamless as possible.

  View details for DOI 10.1038/nature21004

  View details for Web of Science ID 000389716800032

  View details for PubMedID 27974769

• High-Performance Lithium Metal Negative Electrode with a Soft and Flowable Polymer Coating ACS ENERGY LETTERS Zheng, G., Wang, C., Pei, A., Lopez, J., Shi, F., Chen, Z., Sendek, A. D., Lee, H., Lu, Z., Schneider, H., Safont-Sempere, M. M., Chu, S., Bao, Z., Cui, Y. 2016; 1 (6): 1247-1255

  View details for DOI 10.1021/acsenergylett.6b00456

  View details for Web of Science ID 000390086400028

• Surpassing the Exciton Diffusion Limit in Single-Walled Carbon Nanotube Sensitized Solar Cells ACS NANO Koleilat, G. I., Vosgueritchian, M., Lei, T., Zhou, Y., Lin, D. W., Lissel, F., Lin, P., To, J. W., Xie, T., England, K., Zhang, Y., Bao, Z. 2016; 10 (12): 11258-11265

  Abstract

  Semiconducting single-walled carbon nanotube (s-SWNT) light sensitized devices, such as infrared photodetectors and solar cells, have recently been widely reported. Despite their excellent individual electrical properties, efficient carrier transport from one carbon nanotube to another remains a fundamental challenge. Specifically, photovoltaic devices with active layers made from s-SWNTs have suffered from low efficiencies caused by three main challenges: the overwhelming presence of high-bandgap polymers in the films, the weak bandgap offset between the LUMO of the s-SWNTs and the acceptor C60, and the limited exciton diffusion length from one SWNT to another of around 5 nm that limits the carrier extraction efficiency. Herein, we employ a combination of processing and device architecture design strategies to address each of these transport challenges and fabricate photovoltaic devices with s-SWNT films well beyond the exciton diffusion limit of 5 nm. While our solution processing method minimizes the presence of undesired polymers in our active films, our interfacial designs led to a significant increase in current generation with the addition of a highly doped C60 layer (n-doped C60), resulting in increased carrier separation efficiency from the s-SWNTs films. We create a dense interconnected nanoporous mesh of s-SWNTs using solution shearing and infiltrate it with the acceptor C60. Thus, our final engineered bulk heterojunction allows carriers from deep within to be extracted by the C60 registering a 10-fold improvement in performance from our preliminary structures.

  View details for DOI 10.1021/acsnano.6b06358

  View details for Web of Science ID 000391079700071

  View details for PubMedID 28024326

• Comparison of the Morphology Development of Polymer-Fullerene and Polymer-Polymer Solar Cells during Solution-Shearing Blade Coating ADVANCED ENERGY MATERIALS Gu, X., Yan, H., Kurosawa, T., Schroeder, B. C., Gu, K. L., Zhou, Y., To, J. W., Oosterhout, S. D., Savikhin, V., Molina-Lopez, F., Tassone, C. J., Mannsfeld, S. C., Wang, C., Toney, M. F., Bao, Z. 2016; 6 (22)

  View details for DOI 10.1002/aenm.201601225

  View details for Web of Science ID 000388993100014

• Doped Organic Transistors CHEMICAL REVIEWS Lussem, B., Keum, C., Kasemann, D., Naab, B., Bao, Z., Leo, K. 2016; 116 (22): 13714-13751

  Abstract

  Organic field-effect transistors hold the promise of enabling low-cost and flexible electronics. Following its success in organic optoelectronics, the organic doping technology is also used increasingly in organic field-effect transistors. Doping not only increases device performance, but it also provides a way to fine-control the transistor behavior, to develop new transistor concepts, and even improve the stability of organic transistors. This Review summarizes the latest progress made in the understanding of the doping technology and its application to organic transistors. It presents the most successful doping models and an overview of the wide variety of materials used as dopants. Further, the influence of doping on charge transport in the most relevant polycrystalline organic semiconductors is reviewed, and a concise overview on the influence of doping on transistor behavior and performance is given. In particular, recent progress in the understanding of contact doping and channel doping is summarized.

  View details for DOI 10.1021/acs.chemrev.6b00329

  View details for Web of Science ID 000388913000010

  View details for PubMedID 27696874

• Intrinsically stretchable and healable semiconducting polymer for organic transistors NATURE Oh, J. Y., Rondeau-Gagne, S., Chiu, Y., Chortos, A., Lissel, F., Wang, G. N., Schroeder, B. C., Kurosawa, T., Lopez, J., Katsumata, T., Xu, J., Zhu, C., Gu, X., Bae, W., Kim, Y., Jin, L., Chung, J. W., Tok, J. B., Bao, Z. 2016; 539 (7629): 411-415

  Abstract

  Thin-film field-effect transistors are essential elements of stretchable electronic devices for wearable electronics. All of the materials and components of such transistors need to be stretchable and mechanically robust. Although there has been recent progress towards stretchable conductors, the realization of stretchable semiconductors has focused mainly on strain-accommodating engineering of materials, or blending of nanofibres or nanowires into elastomers. An alternative approach relies on using semiconductors that are intrinsically stretchable, so that they can be fabricated using standard processing methods. Molecular stretchability can be enhanced when conjugated polymers, containing modified side-chains and segmented backbones, are infused with more flexible molecular building blocks. Here we present a design concept for stretchable semiconducting polymers, which involves introducing chemical moieties to promote dynamic non-covalent crosslinking of the conjugated polymers. These non-covalent crosslinking moieties are able to undergo an energy dissipation mechanism through breakage of bonds when strain is applied, while retaining high charge transport abilities. As a result, our polymer is able to recover its high field-effect mobility performance (more than 1 square centimetre per volt per second) even after a hundred cycles at 100 per cent applied strain. Organic thin-film field-effect transistors fabricated from these materials exhibited mobility as high as 1.3 square centimetres per volt per second and a high on/off current ratio exceeding a million. The field-effect mobility remained as high as 1.12 square centimetres per volt per second at 100 per cent strain along the direction perpendicular to the strain. The field-effect mobility of damaged devices can be almost fully recovered after a solvent and thermal healing treatment. Finally, we successfully fabricated a skin-inspired stretchable organic transistor operating under deformations that might be expected in a wearable device.

  View details for DOI 10.1038/nature20102

  View details for Web of Science ID 000388161700050

  View details for PubMedID 27853213

• Skin-inspired organic electronic materials and devices MRS BULLETIN Bao, Z. 2016; 41 (11): 897-902

  View details for DOI 10.1557/mrs.2016.247

  View details for Web of Science ID 000389136500017

• Inducing Elasticity through Oligo-Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers ADVANCED FUNCTIONAL MATERIALS Wang, G. N., Shaw, L., Xu, J., Kurosawa, T., Schroeder, B. C., Oh, J. Y., Benight, S. J., Bao, Z. 2016; 26 (40): 7254-7262

  View details for DOI 10.1002/adfm.201602603

  View details for Web of Science ID 000387545200005

• A Stiff and Healable Polymer Based on Dynamic-Covalent Boroxine Bonds ADVANCED MATERIALS Lai, J., Mei, J., Jia, X., Li, C., You, X., Bao, Z. 2016; 28 (37): 8277-8282

  Abstract

  A stiff and healable polymer is obtained by using the dynamic-covalent boroxine bond to crosslink PDMS chain into 3D networks. The as-prepared polymer is very strong and stiff, and can bear a load of more than 450 times its weight. When damaged, it can be completely healed upon heating after wetting.

  View details for DOI 10.1002/adma.201602332

  View details for Web of Science ID 000386103600024

  View details for PubMedID 27387198

• A Highly Stretchable and Autonomous Self-Healing Polymer Based on Combination of Pt center dot center dot center dot Pt and pi-pi Interactions MACROMOLECULAR RAPID COMMUNICATIONS Mei, J., Jia, X., Lai, J., Sun, Y., Li, C., Wu, J., Cao, Y., You, X., Bao, Z. 2016; 37 (20): 1667-1675

  Abstract

  A new self-healing polymer has been obtained by incorporating a cyclometalated platinum(II) complex Pt(C(∧) N(∧) N)Cl (C(∧) N(∧) N = 6-phenyl-2,2'-bipyridyl) into a polydimethylsiloxane (PDMS) backbone. The molecular interactions (a combination of Pt···Pt and π-π interactions) between cyclometalated platinum(II) complexes are strong enough to crosslink the linear PDMS polymer chains into an elastic film. The as prepared polymer can be stretched to over 20 times of its original length. When damaged, the polymer can be healed at room temperature without any healants or external stimuli. Moreover, the self-healing is insensitive to surface aging. This work represents the first example where the attractive metallophilic inter-actions are utilized to design self-healing materials. Moreover, our results suggest that the stretchability and self-healing properties can be obtained simultaneously without any conflict by optimizing the strength of crosslinking interactions.

  View details for DOI 10.1002/marc.201600428

  View details for Web of Science ID 000386631200005

• A Highly Stretchable and Autonomous Self-Healing Polymer Based on Combination of Pt···Pt and p-p Interactions. Macromolecular rapid communications Mei, J., Jia, X., Lai, J., Sun, Y., Li, C., Wu, J., Cao, Y., You, X., Bao, Z. 2016; 37 (20): 1667-1675

  Abstract

  A new self-healing polymer has been obtained by incorporating a cyclometalated platinum(II) complex Pt(C(∧) N(∧) N)Cl (C(∧) N(∧) N = 6-phenyl-2,2'-bipyridyl) into a polydimethylsiloxane (PDMS) backbone. The molecular interactions (a combination of Pt···Pt and π-π interactions) between cyclometalated platinum(II) complexes are strong enough to crosslink the linear PDMS polymer chains into an elastic film. The as prepared polymer can be stretched to over 20 times of its original length. When damaged, the polymer can be healed at room temperature without any healants or external stimuli. Moreover, the self-healing is insensitive to surface aging. This work represents the first example where the attractive metallophilic inter-actions are utilized to design self-healing materials. Moreover, our results suggest that the stretchability and self-healing properties can be obtained simultaneously without any conflict by optimizing the strength of crosslinking interactions.

  View details for DOI 10.1002/marc.201600428

  View details for PubMedID 27569252

• Pursuing prosthetic electronic skin. Nature materials Chortos, A., Liu, J., Bao, Z. 2016; 15 (9): 937-950

  Abstract

  Skin plays an important role in mediating our interactions with the world. Recreating the properties of skin using electronic devices could have profound implications for prosthetics and medicine. The pursuit of artificial skin has inspired innovations in materials to imitate skin's unique characteristics, including mechanical durability and stretchability, biodegradability, and the ability to measure a diversity of complex sensations over large areas. New materials and fabrication strategies are being developed to make mechanically compliant and multifunctional skin-like electronics, and improve brain/machine interfaces that enable transmission of the skin's signals into the body. This Review will cover materials and devices designed for mimicking the skin's ability to sense and generate biomimetic signals.

  View details for DOI 10.1038/nmat4671

  View details for PubMedID 27376685

• Investigation of a Solution-Processable, Nonspecific Surface Modifier for Low Cost, High Work Function Electrodes. ACS applied materials & interfaces Hinckley, A. C., Wang, C., Pfattner, R., Kong, D., Zhou, Y., Ecker, B., Gao, Y., Bao, Z. 2016; 8 (30): 19658-19664

  Abstract

  We demonstrate the ability of the highly fluorinated, chemically inert copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to significantly increase the work function of a variety of common electrode materials. The work function change is hypothesized to occur via physisorption of the polymer layer and formation of a surface dipole at the polymer/conductor interface. When incorporated into organic solar cells, an interlayer of PVDF-HFP at an Ag anode increases the open circuit voltage by 0.4 eV and improves device power conversion efficiency by approximately an order of magnitude relative to Ag alone. Solution-processable in air, PVDF-HFP thin films provide one possible route toward achieving low cost, nonreactive, high work function electrodes.

  View details for DOI 10.1021/acsami.6b05348

  View details for PubMedID 27428045

• All-Polymer Solar Cells Employing Non-Halogenated Solvent and Additive CHEMISTRY OF MATERIALS Zhou, Y., Gu, K. L., Gu, X., Kurosawa, T., Yan, H., Guo, Y., Koleilat, G. I., Zhao, D., Toney, M. F., Bao, Z. 2016; 28 (14): 5037-5042

  View details for DOI 10.1021/acs.chemmater.6b01776

  View details for Web of Science ID 000380576700020

• Tunable Polyaniline-Based Porous Carbon with Ultrahigh Surface Area for CO2 Capture at Elevated Pressure ADVANCED ENERGY MATERIALS He, J., To, J. W., Psarras, P. C., Yan, H., Atkinson, T., Holmes, R. T., Nordlund, D., Bao, Z., Wilcox, J. 2016; 6 (14)

  View details for DOI 10.1002/aenm.201502491

  View details for Web of Science ID 000381693700002

• Capacitance Characterization of Elastomeric Dielectrics for Applications in Intrinsically Stretchable Thin Film Transistors ADVANCED FUNCTIONAL MATERIALS Kong, D., Pfattner, R., Chortos, A., Lu, C., Hinckley, A. C., Wang, C., Lee, W., Chung, J. W., Bao, Z. 2016; 26 (26): 4680-4686

  View details for DOI 10.1002/adfm.201600612

  View details for Web of Science ID 000380887300007

• Combinatorial Study of Temperature-Dependent Nanostructure and Electrical Conduction of Polymer Semiconductors: Even Bimodal Orientation Can Enhance 3D Charge Transport ADVANCED FUNCTIONAL MATERIALS Park, S., Lee, M. H., Ahn, K. S., Choi, H. H., Shin, J., Xu, J., Mei, J., Cho, K., Bao, Z., Lee, D. R., Kang, M. S., Kim, D. H. 2016; 26 (26): 4627-4634

  View details for DOI 10.1002/adfm.201601164

  View details for Web of Science ID 000380887300001

• Non-Conjugated Flexible Linkers in Semiconducting Polymers: A Pathway to Improved Processability without Compromising Device Performance ADVANCED ELECTRONIC MATERIALS Schroeder, B. C., Chiu, Y., Gu, X., Zhou, Y., Xu, J., Lopez, J., Lu, C., Toney, M. F., Bao, Z. 2016; 2 (7)

  View details for DOI 10.1002/aelm.201600104

  View details for Web of Science ID 000379913000010

• Mechanically Durable and Highly Stretchable Transistors Employing Carbon Nanotube Semiconductor and Electrodes ADVANCED MATERIALS Chortos, A., Koleilat, G. I., Pfattner, R., Kong, D., Lin, P., Nur, R., Lei, T., Wang, H., Liu, N., Lai, Y., Kim, M., Chung, J. W., Lee, S., Bao, Z. 2016; 28 (22): 4441-?

  Abstract

  Mechanically durable stretchable trans-istors are fabricated using carbon nanotube electrical components and tough thermoplastic elastomers. After an initial conditioning step, the electrical characteristics remain constant with strain. The strain-dependent characteristics are similar in orthogonal stretching directions. Devices can be impacted with a hammer and punctured with a needle while remaining functional and stretchable.

  View details for DOI 10.1002/adma.201501828

  View details for PubMedID 26179120

• A highly stretchable autonomous self-healing elastomer NATURE CHEMISTRY Li, C., Wang, C., Keplinger, C., Zuo, J., Jin, L., Sun, Y., Zheng, P., Cao, Y., Lissel, F., Linder, C., You, X., Bao, Z. 2016; 8 (6): 619-625

  Abstract

  It is a challenge to synthesize materials that possess the properties of biological muscles-strong, elastic and capable of self-healing. Herein we report a network of poly(dimethylsiloxane) polymer chains crosslinked by coordination complexes that combines high stretchability, high dielectric strength, autonomous self-healing and mechanical actuation. The healing process can take place at a temperature as low as -20 °C and is not significantly affected by surface ageing and moisture. The crosslinking complexes used consist of 2,6-pyridinedicarboxamide ligands that coordinate to Fe(III) centres through three different interactions: a strong pyridyl-iron one, and two weaker carboxamido-iron ones through both the nitrogen and oxygen atoms of the carboxamide groups. As a result, the iron-ligand bonds can readily break and re-form while the iron centres still remain attached to the ligands through the stronger interaction with the pyridyl ring, which enables reversible unfolding and refolding of the chains. We hypothesize that this behaviour supports the high stretchability and self-healing capability of the material.

  View details for DOI 10.1038/NCHEM.2492

  View details for Web of Science ID 000376529000020

• A highly stretchable autonomous self-healing elastomer. Nature chemistry Li, C., Wang, C., Keplinger, C., Zuo, J., Jin, L., Sun, Y., Zheng, P., Cao, Y., Lissel, F., Linder, C., You, X., Bao, Z. 2016; 8 (6): 618-624

  Abstract

  It is a challenge to synthesize materials that possess the properties of biological muscles-strong, elastic and capable of self-healing. Herein we report a network of poly(dimethylsiloxane) polymer chains crosslinked by coordination complexes that combines high stretchability, high dielectric strength, autonomous self-healing and mechanical actuation. The healing process can take place at a temperature as low as -20 °C and is not significantly affected by surface ageing and moisture. The crosslinking complexes used consist of 2,6-pyridinedicarboxamide ligands that coordinate to Fe(III) centres through three different interactions: a strong pyridyl-iron one, and two weaker carboxamido-iron ones through both the nitrogen and oxygen atoms of the carboxamide groups. As a result, the iron-ligand bonds can readily break and re-form while the iron centres still remain attached to the ligands through the stronger interaction with the pyridyl ring, which enables reversible unfolding and refolding of the chains. We hypothesize that this behaviour supports the high stretchability and self-healing capability of the material.

  View details for DOI 10.1038/nchem.2492

  View details for PubMedID 27219708

• 3D Porous Sponge-Inspired Electrode for Stretchable Lithium-Ion Batteries ADVANCED MATERIALS Liu, W., Chen, Z., Zhou, G., Sun, Y., Lee, H. R., Liu, C., Yao, H., Bao, Z., Cui, Y. 2016; 28 (18): 3578-?

  Abstract

  A stretchable Li4 Ti5 O12 anode and a LiFePO4 cathode with 80% stretchability are prepared using a 3D interconnected porous polydimethylsiloxane sponge based on sugar cubes. 82% and 91% capacity retention for anode and cathode are achieved after 500 stretch-release cycles. Slight capacity decay of 6% in the battery using the electrode in stretched state is observed.

  View details for DOI 10.1002/adma.201505299

  View details for PubMedID 26992146

• Stretchable Self-Healing Polymeric Dielectrics Cross-Linked Through Metal-Ligand Coordination JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Rao, Y., Chortos, A., Pfattner, R., Lissel, F., Chiu, Y., Feig, V., Xu, J., Kurosawa, T., Gu, X., Wang, C., He, M., Chung, J. W., Bao, Z. 2016; 138 (18): 6020-6027

  Abstract

  A self-healing dielectric elastomer is achieved by the incorporation of metal-ligand coordination as cross-linking sites in nonpolar polydimethylsiloxane (PDMS) polymers. The ligand is 2,2'-bipyridine-5,5'-dicarboxylic amide, while the metal salts investigated here are Fe(2+) and Zn(2+) with various counteranions. The kinetically labile coordination between Zn(2+) and bipyridine endows the polymer fast self-healing ability at ambient condition. When integrated into organic field-effect transistors (OFETs) as gate dielectrics, transistors with FeCl2 and ZnCl2 salts cross-linked PDMS exhibited increased dielectric constants compared to PDMS and demonstrated hysteresis-free transfer characteristics, owing to the low ion conductivity in PDMS and the strong columbic interaction between metal cations and the small Cl(-) anions which can prevent mobile anions drifting under gate bias. Fully stretchable transistors with FeCl2-PDMS dielectrics were fabricated and exhibited ideal transfer characteristics. The gate leakage current remained low even after 1000 cycles at 100% strain. The mechanical robustness and stable electrical performance proved its suitability for applications in stretchable electronics. On the other hand, transistors with gate dielectrics containing large-sized anions (BF4(-), ClO4(-), CF3SO3(-)) displayed prominent hysteresis due to mobile anions drifting under gate bias voltage. This work provides insights on future design of self-healing stretchable dielectric materials based on metal-ligand cross-linked polymers.

  View details for DOI 10.1021/jacs.6b02428

  View details for Web of Science ID 000375889100044

  View details for PubMedID 27099162

• Role of Polymer Structure on the Conductivity of N-Doped Polymers ADVANCED ELECTRONIC MATERIALS Naab, B. D., Gu, X., Kurosawa, T., To, J. W., Salleo, A., Bao, Z. 2016; 2 (5)

  View details for DOI 10.1002/aelm.201600004

  View details for Web of Science ID 000377583600020

• Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing. ACS applied materials & interfaces Shaw, L., Hayoz, P., Diao, Y., Reinspach, J. A., To, J. W., Toney, M. F., Weitz, R. T., Bao, Z. 2016; 8 (14): 9285-9296

  Abstract

  The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used to tune polymer alignment in a one-step deposition process not requiring substrate patterning or any postdeposition treatment.

  View details for DOI 10.1021/acsami.6b01607

  View details for PubMedID 26985638

• A Stretchable Graphitic Carbon/Si Anode Enabled by Conformal Coating of a Self-Healing Elastic Polymer ADVANCED MATERIALS Sun, Y., Lopez, J., Lee, H., Liu, N., Zheng, G., Wu, C., Sun, J., Liu, W., Chung, J. W., Bao, Z., Cui, Y. 2016; 28 (12): 2455-2461

  Abstract

  A high-capacity stretchable graphitic carbon/Si foam electrode is enabled by a conformal self-healing elastic polymer coating. The composite electrode exhibits high stretchability (up to 88%) and endures 1000 stretching-releasing cycles at 25% strain with detrimental resistance increase. Meanwhile, the electrode delivers a high reversible specific capacity of 719 mA g(-1) and good cycling stability with 81% capacity retention after 100 cycles.

  View details for DOI 10.1002/adma.201504723

  View details for Web of Science ID 000372459600022

• A Stretchable Graphitic Carbon/Si Anode Enabled by Conformal Coating of a Self-Healing Elastic Polymer. Advanced materials Sun, Y., Lopez, J., Lee, H., Liu, N., Zheng, G., Wu, C., Sun, J., Liu, W., Chung, J. W., Bao, Z., Cui, Y. 2016; 28 (12): 2455-2461

  Abstract

  A high-capacity stretchable graphitic carbon/Si foam electrode is enabled by a conformal self-healing elastic polymer coating. The composite electrode exhibits high stretchability (up to 88%) and endures 1000 stretching-releasing cycles at 25% strain with detrimental resistance increase. Meanwhile, the electrode delivers a high reversible specific capacity of 719 mA g(-1) and good cycling stability with 81% capacity retention after 100 cycles.

  View details for DOI 10.1002/adma.201504723

  View details for PubMedID 26813780

• Impact of Polystyrene Oligomer Side Chains on Naphthalene Diimide-Bithiophene Polymers as n-Type Semiconductors for Organic Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Kurosawa, T., Chiu, Y., Zhou, Y., Gu, X., Chen, W., Bao, Z. 2016; 26 (8): 1261-1270

  View details for DOI 10.1002/adfm.201504255

  View details for Web of Science ID 000371078100013

• Hierarchical N-Doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor JOURNAL OF THE AMERICAN CHEMICAL SOCIETY To, J. W., He, J., Mei, J., Haghpanah, R., Chen, Z., Kurosawa, T., Chen, S., Bae, W., Pan, L., Tok, J. B., Wilcox, J., Bao, Z. 2016; 138 (3): 1001-1009

  Abstract

  Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry's law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultrasmall pores (d < 0.5 nm) and preservation of nitrogen moieties, essential for enhanced CO2 affinity. Furthermore, our described work provides a strategy to initiate developments of rationally designed porous conjugated polymer structures and carbon-based materials for various potential applications.

  View details for DOI 10.1021/jacs.5b11955

  View details for Web of Science ID 000369044400047

  View details for PubMedID 26717034

• Tuning the Morphology of Solution-Sheared P3HT:PCBM Films ACS APPLIED MATERIALS & INTERFACES Reinspach, J. A., Diao, Y., Giri, G., Sachse, T., England, K., Zhou, Y., Tassone, C., Worfolk, B. J., Presselt, M., Toney, M. F., Mannsfeld, S., Bao, Z. 2016; 8 (3): 1742-1751

  Abstract

  Organic bulk heterojunction (BHJ) solar cells are a promising alternative for future clean-energy applications. However, to become attractive for consumer applications, such as wearable, flexible, or semitransparent power-generating electronics, they need to be manufactured by high-throughput, low-cost, large-area-capable printing techniques. However, most research reported on BHJ solar cells is conducted using spin coating, a single batch fabrication method, thus limiting the reported results to the research lab. In this work, we investigate the morphology of solution-sheared films for BHJ solar cell applications, using the widely studied model blend P3HT:PCBM. Solution shearing is a coating technique that is upscalable to industrial manufacturing processes and has demonstrated to yield record performance organic field-effect transistors. Using grazing incident small-angle X-ray scattering, grazing incident wide-angle X-ray scattering, and UV-vis spectroscopy, we investigate the influence of solvent, film drying time, and substrate temperature on P3HT aggregation, conjugation length, crystallite orientation, and PCBM domain size. One important finding of this study is that, in contrast to spin-coated films, the P3HT molecular orientation can be controlled by the substrate chemistry, withPSS substrates yielding face-on orientation at the substrate-film interface, an orientation highly favorable for organic solar cells.

  View details for DOI 10.1021/acsami.5b09349

  View details for Web of Science ID 000369044100024

  View details for PubMedID 26771274

• The Effects of Cross-Linking in a Supramolecular Binder on Cycle Life in Silicon Microparticle Anodes. ACS applied materials & interfaces Lopez, J., Chen, Z., Wang, C., Andrews, S. C., Cui, Y., Bao, Z. 2016; 8 (3): 2318-2324

  Abstract

  Self-healing supramolecular binder was previously found to enhance the cycling stability of micron-sized silicon particles used as the active material in lithium-ion battery anodes. In this study, we systematically control the density of cross-linking junctions in a modified supramolecular polymer binder in order to better understand how viscoelastic materials properties affect cycling stability. We found that binders with relaxation times on the order of 0.1 s gave the best cycling stability with 80% capacity maintained for over 175 cycles using large silicon particles (∼0.9 um). We attributed this to an improved balance between the viscoelastic stress relaxation in the binder and the stiffness needed to maintain mechanical integrity of the electrode. The more cross-linked binder showed markedly worse performance confirming the need for liquid-like flow in order for our self-healing polymer electrode concept to be effective.

  View details for DOI 10.1021/acsami.5b11363

  View details for PubMedID 26716873

• Removable and Recyclable Conjugated Polymers for Highly Selective and High-Yield Dispersion and Release of Low-Cost Carbon Nanotubes. Journal of the American Chemical Society Lei, T., Chen, X., Pitner, G., Wong, H. P., Bao, Z. 2016; 138 (3): 802-805

  Abstract

  High-purity semiconducting single-walled carbon nanotubes (s-SWNTs) with little contamination are desired for high-performance electronic devices. Although conjugated polymer wrapping has been demonstrated as a powerful and scalable strategy for enriching s-SWNTs, this approach suffers from significant contaminations by polymer residues and high cost of conjugated polymers. Here, we present a simple but general approach using removable and recoverable conjugated polymers for separating s-SWNTs with little polymer contamination. A conjugated polymer with imine linkages was synthesized to demonstrate this concept. Moreover, the SWNTs used are without prepurifications and very low cost. The polymer exhibits strong dispersion for large-diameter s-SWNTs with high yield (23.7%) and high selectivity (99.7%). After s-SWNT separation, the polymer can be depolymerized into monomers and be cleanly removed under mild acidic conditions, yielding polymer-free s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize polymer. This approach enables isolation of "clean" s-SWNTs and, at the same time, greatly lowers costs for SWNT separation.

  View details for DOI 10.1021/jacs.5b12797

  View details for PubMedID 26731376

• Compact Roll-to-Roll Coater for in Situ X-ray Diffraction Characterization of Organic Electronics Printing. ACS applied materials & interfaces Gu, X., Reinspach, J., Worfolk, B. J., Diao, Y., Zhou, Y., Yan, H., Gu, K., Mannsfeld, S., Toney, M. F., Bao, Z. 2016; 8 (3): 1687-1694

  Abstract

  We describe a compact roll-to-roll (R2R) coater that is capable of tracking the crystallization process of semiconducting polymers during solution printing using X-ray scattering at synchrotron beamlines. An improved understanding of the morphology evolution during the solution-processing of organic semiconductor materials during R2R coating processes is necessary to bridge the gap between "lab" and "fab". The instrument consists of a vacuum chuck to hold the flexible plastic substrate uniformly flat for grazing incidence X-ray scattering. The time resolution of the drying process that is achievable can be tuned by controlling two independent motor speeds, namely, the speed of the moving flexible substrate and the speed of the printer head moving in the opposite direction. With this novel design, we are able to achieve a wide range of drying time resolutions, from tens of milliseconds to seconds. This allows examination of the crystallization process over either fast or slow drying processes depending on coating conditions. Using regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) inks based on two different solvents as a model system, we demonstrate the capability of our in situ R2R printing tool by observing two distinct crystallization processes for inks drying from the solvents with different boiling points (evaporation rates). We also observed delayed on-set point for the crystallization of P3HT polymer in the 1:1 P3HT/PCBM BHJ blend, and the inhibited crystallization of the P3HT during the late stage of the drying process.

  View details for DOI 10.1021/acsami.5b09174

  View details for PubMedID 26714412

• Fast and reversible thermoresponsive polymer switching materials for safer batteries NATURE ENERGY Chen, Z., Hsu, P., Lopez, J., Li, Y., To, J. W., Liu, N., Wang, C., Andrews, S. C., Liu, J., Cui, Y., Bao, Z. 2016; 1

  View details for DOI 10.1038/NENERGY.2015.9

  View details for Web of Science ID 000394094100009

• Semiconducting Carbon Nanotubes for Improved Efficiency and Thermal Stability of Polymer-Fullerene Solar Cells ADVANCED FUNCTIONAL MATERIALS Salim, T., Lee, H., Wong, L. H., Oh, J. H., Bao, Z., Lam, Y. M. 2016; 26 (1): 51-65

  View details for DOI 10.1002/adfm.201503256

  View details for Web of Science ID 000368039700006

• Dispersion of High-Purity Semiconducting Arc-Discharged Carbon Nanotubes Using Backbone Engineered Diketopyrrolopyrrole (DPP)-Based Polymers ADVANCED ELECTRONIC MATERIALS Lei, T., Pitner, G., Chen, X., Hong, G., Park, S., Hayoz, P., Weitz, R. T., Wong, H. P., Bao, Z. 2016; 2 (1)

  View details for DOI 10.1002/aelm.201500299

  View details for Web of Science ID 000370335000018

• A sensor measuring deformation and pressure, entirely biodegradable, for orthopedic applications Boutry, C. M., Schroeder, B. C., Bao, Z., Legrand, A., Fox, P., IEEE IEEE. 2016: 144-147

  View details for Web of Science ID 000401795900043

• OFETs: BASIC CONCEPTS AND MATERIAL DESIGNS WSPC REFERENCE ON ORGANIC ELECTRONICS: ORGANIC SEMICONDUCTORS, VOL: 2: FUNDAMENTAL ASPECTS OF MATERIALS AND APPLICATIONS Lee, W., Mei, J., Bao, Z., Bredas, J. L., Marder 2016; 7: 19-83

  View details for Web of Science ID 000467594700002

• Development of Organic Semiconducting Technology to Realize Low Driving Voltages He, M., Wang, C., Lee, W., Kong, D., Pfattner, R., Niu, W., Matthews, J. R., Wallace, A., Bao, Z., IEEE IEEE. 2016: 33-35

  View details for Web of Science ID 000389600900010

• Flexible and Stretchable Devices. Advanced materials (Deerfield Beach, Fla.) Bao, Z. n., Chen, X. n. 2016; 28 (22): 4177–79

  View details for PubMedID 27273438

• An ultra-narrow bandgap derived from thienoisoindigo polymers: structural influence on reducing the bandgap and self-organization POLYMER CHEMISTRY Hasegawa, T., Ashizawa, M., Hiyoshi, J., Kawauchi, S., Mei, J., Bao, Z., Matsumoto, H. 2016; 7 (5): 1181-1190

  View details for DOI 10.1039/c5py01870f

  View details for Web of Science ID 000368896300018

• Direct imaging of rotating molecules anchored on graphene NANOSCALE Choe, J., Lee, Y., Fang, L., Lee, G., Bao, Z., Kim, K. 2016; 8 (27): 13174-13180

  Abstract

  There has been significant research interest in controlling and imaging molecular dynamics, such as translational and rotational motions, especially at a single molecular level. Here we applied aberration-corrected transmission electron microscopy (ACTEM) to actuate and directly image the rotational motions of molecules anchored on a single-layer-graphene sheet. Nanometer-sized carbonaceous molecules anchored on graphene provide ideal systems for monitoring rotational motions via ACTEM. We observed the preferential registry of longer molecular axis along graphene zigzag or armchair lattice directions due to the stacking-dependent molecule-graphene energy landscape. The calculated cross section from elastic scattering theory was used to experimentally estimate the rotational energy barriers of molecules on graphene. The observed energy barrier was within the range of 1.5-12 meV per atom, which is in good agreement with previous calculation results. We also performed molecular dynamics simulations, which revealed that the edge atoms of the molecule form stably bonds to graphene defects and can serve as a pivot point for rotational dynamics. Our study demonstrates the versatility of ACTEM for the investigation of molecular dynamics and configuration-dependent energetics at a single molecular level.

  View details for DOI 10.1039/c6nr04251a

  View details for Web of Science ID 000379489000005

  View details for PubMedID 27333828

• Impact of the Crystallite Orientation Distribution on Exciton Transport in Donor-Acceptor Conjugated Polymers ACS APPLIED MATERIALS & INTERFACES Ayzner, A. L., Mei, J., Appleton, A., DeLongchamp, D., Nardes, A., Benight, S., Kopidakis, N., Toney, M. F., Bao, Z. 2015; 7 (51): 28035-28041

  Abstract

  Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their extended electronic wave functions, they often form semicrystalline thin films. In this work, we aim to understand whether distribution of crystallographic orientations affects exciton diffusion using a low-band-gap polymer backbone motif that is representative of the donor/acceptor copolymer class. Using the fact that the polymer side chain can tune the dominant crystallographic orientation in the thin film, we have measured the quenching of polymer photoluminescence, and thus the extent of exciton dissociation, as a function of crystal orientation with respect to a quenching substrate. We find that the crystallite orientation distribution has little effect on the average exciton diffusion length. We suggest several possibilities for the lack of correlation between crystallographic texture and exciton transport in semicrystalline conjugated polymer films.

  View details for DOI 10.1021/acsami.5b02968

  View details for Web of Science ID 000369448200008

  View details for PubMedID 26292836

• Fabrication of flexible pressure sensors with microstructured polydimethylsiloxane dielectrics using the breath figures method JOURNAL OF MATERIALS RESEARCH Miller, S., Bao, Z. 2015; 30 (23): 3584-3594

  View details for DOI 10.1557/jmr.2015.334

  View details for Web of Science ID 000367253100003

• Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors SCIENTIFIC REPORTS Wang, C., Lee, W., Kong, D., Pfattner, R., Schweicher, G., Nakajima, R., Lu, C., Mei, J., Lee, T. H., Wu, H., Lopez, J., Diao, Y., Gu, X., Himmelberger, S., Niu, W., Matthews, J. R., He, M., Salleo, A., Nishi, Y., Bao, Z. 2015; 5

  Abstract

  Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10(-10) S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water.

  View details for DOI 10.1038/srep17849

  View details for PubMedID 26658331

• Conjugated polymer sorting of semiconducting carbon nanotubes and their electronic applications NANO TODAY Wang, H., Bao, Z. 2015; 10 (6): 737-758

  View details for DOI 10.1016/j.nantod.2015.11.008

  View details for Web of Science ID 000370906400009

• A Sensitive and Biodegradable Pressure Sensor Array for Cardiovascular Monitoring ADVANCED MATERIALS Boutry, C. M., Nguyen, A., Lawal, Q. O., Chortos, A., Rondeau-Gagne, S., Bao, Z. 2015; 27 (43): 6954-?

  Abstract

  An array of highly sensitive pressure sensors entirely made of biodegradable materials is presented, designed as a single-use flexible patch for application in cardiovascular monitoring. The high sensitivity in combination with fast response time is unprecedented when compared to recent reports on biodegradable pressure sensors (sensitivity three orders of magnitude higher), as illustrated by pulse wave velocity measurements, toward hypertension detection.

  View details for DOI 10.1002/adma.201502535

  View details for Web of Science ID 000366402500024

• A Sensitive and Biodegradable Pressure Sensor Array for Cardiovascular Monitoring. Advanced materials (Deerfield Beach, Fla.) Boutry, C. M., Nguyen, A., Lawal, Q. O., Chortos, A., Rondeau-Gagné, S., Bao, Z. 2015; 27 (43): 6954-61

  Abstract

  An array of highly sensitive pressure sensors entirely made of biodegradable materials is presented, designed as a single-use flexible patch for application in cardiovascular monitoring. The high sensitivity in combination with fast response time is unprecedented when compared to recent reports on biodegradable pressure sensors (sensitivity three orders of magnitude higher), as illustrated by pulse wave velocity measurements, toward hypertension detection.

  View details for DOI 10.1002/adma.201502535

  View details for PubMedID 26418964

• Ultrahigh electrical conductivity in solution-sheared polymeric transparent films. Proceedings of the National Academy of Sciences of the United States of America Worfolk, B. J., Andrews, S. C., Park, S., Reinspach, J., Liu, N., Toney, M. F., Mannsfeld, S. C., Bao, Z. 2015; 112 (46): 14138-14143

  Abstract

  With consumer electronics transitioning toward flexible products, there is a growing need for high-performance, mechanically robust, and inexpensive transparent conductors (TCs) for optoelectronic device integration. Herein, we report the scalable fabrication of highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PSS) thin films via solution shearing. Specific control over deposition conditions allows for tunable phase separation and preferential PEDOT backbone alignment, resulting in record-high electrical conductivities of 4,600 ± 100 S/cm while maintaining high optical transparency. High-performance solution-sheared TC PEDOT:PSS films were used as patterned electrodes in capacitive touch sensors and organic photovoltaics to demonstrate practical viability in optoelectronic applications.

  View details for DOI 10.1073/pnas.1509958112

  View details for PubMedID 26515096

  View details for PubMedCentralID PMC4655535

• Partially-Screened Field Effect and Selective Carrier Injection at Organic Semiconductor/Graphene Heterointerface NANO LETTERS Shih, C., Pfattner, R., Chiu, Y., Liu, N., Lei, T., Kong, D., Kim, Y., Chou, H., Bae, W., Bao, Z. 2015; 15 (11): 7587-7595

  Abstract

  Due to the lack of a bandgap, applications of graphene require special device structures and engineering strategies to enable semiconducting characteristics at room temperature. To this end, graphene-based vertical field-effect transistors (VFETs) are emerging as one of the most promising candidates. Previous work attributed the current modulation primarily to gate-modulated graphene-semiconductor Schottky barrier. Here, we report the first experimental evidence that the partially screened field effect and selective carrier injection through graphene dominate the electronic transport at the organic semiconductor/graphene heterointerface. The new mechanistic insight allows us to rationally design graphene VFETs. Flexible organic/graphene VFETs with bending radius <1 mm and the output current per unit layout area equivalent to that of the best oxide planar FETs can be achieved. We suggest driving organic light emitting diodes with such VFETs as a promising application.

  View details for DOI 10.1021/acs.nanolett.5b03378

  View details for Web of Science ID 000364725400062

  View details for PubMedID 26496513

• A skin-inspired organic digital mechanoreceptor SCIENCE Tee, B. C., Chortos, A., Berndt, A., Nguyen, A. K., Tom, A., McGuire, A., Lin, Z. C., Tien, K., Bae, W., Wang, H., Mei, P., Chou, H., Cui, B., Deisseroth, K., Ng, T. N., Bao, Z. 2015; 350 (6258): 313-?

  Abstract

  Human skin relies on cutaneous receptors that output digital signals for tactile sensing in which the intensity of stimulation is converted to a series of voltage pulses. We present a power-efficient skin-inspired mechanoreceptor with a flexible organic transistor circuit that transduces pressure into digital frequency signals directly. The output frequency ranges between 0 and 200 hertz, with a sublinear response to increasing force stimuli that mimics slow-adapting skin mechanoreceptors. The output of the sensors was further used to stimulate optogenetically engineered mouse somatosensory neurons of mouse cortex in vitro, achieving stimulated pulses in accordance with pressure levels. This work represents a step toward the design and use of large-area organic electronic skins with neural-integrated touch feedback for replacement limbs.

  View details for DOI 10.1126/science.aaa9306

  View details for Web of Science ID 000362838700039

  View details for PubMedID 26472906

• Few-layer, large-area, 2D covalent organic framework semiconductor thin films. Chemical communications (Cambridge, England) Feldblyum, J. I., McCreery, C. H., Andrews, S. C., Kurosawa, T., Santos, E. J., Duong, V., Fang, L., Ayzner, A. L., Bao, Z. 2015; 51 (73): 13894-7

  Abstract

  In this work, we synthesize large-area thin films of a conjugated, imine-based, two-dimensional covalent organic framework at the solution/air interface. Thicknesses between ∼2-200 nm are achieved. Films can be transferred to any desired substrate by lifting from underneath, enabling their use as the semiconducting active layer in field-effect transistors.

  View details for DOI 10.1039/c5cc04679c

  View details for PubMedID 26234770

• Diketopyrrolopyrrole-Based Semiconducting Polymer Nanoparticles for In Vivo Photoacoustic Imaging. Advanced materials Pu, K., Mei, J., Jokerst, J. V., Hong, G., Antaris, A. L., Chattopadhyay, N., Shuhendler, A. J., Kurosawa, T., Zhou, Y., Gambhir, S. S., Bao, Z., Rao, J. 2015; 27 (35): 5184-5190

  Abstract

  Diketopyrrolopyrrole-based semiconducting polymer nanoparticles with high photostability and strong photoacoustic brightness are designed and synthesized, which results in 5.3-fold photoacoustic signal enhancement in tumor xenografts after systemic administration.

  View details for DOI 10.1002/adma.201502285

  View details for PubMedID 26247171

  View details for PubMedCentralID PMC4567488

• Shape-Controlled, Self-Wrapped Carbon Nanotube 3D Electronics. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Wang, H., Wang, Y., Tee, B. C., Kim, K., Lopez, J., Cai, W., Bao, Z. 2015; 2 (9): 1500103

  Abstract

  The mechanical flexibility and structural softness of ultrathin devices based on organic thin films and low-dimensional nanomaterials have enabled a wide range of applications including flexible display, artificial skin, and health monitoring devices. However, both living systems and inanimate systems that are encountered in daily lives are all 3D. It is therefore desirable to either create freestanding electronics in a 3D form or to incorporate electronics onto 3D objects. Here, a technique is reported to utilize shape-memory polymers together with carbon nanotube flexible electronics to achieve this goal. Temperature-assisted shape control of these freestanding electronics in a programmable manner is demonstrated, with theoretical analysis for understanding the shape evolution. The shape control process can be executed with prepatterned heaters, desirable for 3D shape formation in an enclosed environment. The incorporation of carbon nanotube transistors, gas sensors, temperature sensors, and memory devices that are capable of self-wrapping onto any irregular shaped-objects without degradations in device performance is demonstrated.

  View details for DOI 10.1002/advs.201500103

  View details for PubMedID 27980972

  View details for PubMedCentralID PMC5115380

• Effect of Chemical Structure on Polymer-Templated Growth of Graphitic Nanoribbons ACS NANO Liu, N., Kim, K., Jeong, H. Y., Hsu, P., Cui, Y., Bao, Z. 2015; 9 (9): 9043-9049

  Abstract

  Graphene nanoribbon (GNR) is an important candidate for future nanoelectronics due to its high carrier mobility and dimension-controlled band gap. Polymer-templated growth is a promising method toward high quality and massive production of GNRs. However, the obtained GNRs so far are still quite defective. In order to rationally control the crystallinity of the synthesized GNRs, herein we systematically investigate the effect of polymer chemical structure on their templated growth of GNRs. We studied the morphology/dimensions, composition, graphitization degree, and electrical conductivity of GNRs derived from four different types of electrospun polymers. The four polymers polystyrene (PS), poly(vinyl alcohol) (PVA), polyvinylphenol (PVP), and Novolac (a phenolic resin) are chosen to investigate the effect of metal binding and the effect of aromatic moieties. We found that metal-binding functional groups are crucial for obtaining uniform and continuous GNRs. On the other hand, a polymer with aromatic moieties leads to a higher sp(2) percentage in the resulting GNRs, showing a higher graphitization degree and electrical conductivity.

  View details for DOI 10.1021/acsnano.5b03134

  View details for Web of Science ID 000361935800042

  View details for PubMedID 26267798

• Shape-Controlled, Self-Wrapped Carbon Nanotube 3D Electronics ADVANCED SCIENCE Wang, H., Wang, Y., Tee, B. C., Kim, K., Lopez, J., Cai, W., Bao, Z. 2015; 2 (9)

  Abstract

  The mechanical flexibility and structural softness of ultrathin devices based on organic thin films and low-dimensional nanomaterials have enabled a wide range of applications including flexible display, artificial skin, and health monitoring devices. However, both living systems and inanimate systems that are encountered in daily lives are all 3D. It is therefore desirable to either create freestanding electronics in a 3D form or to incorporate electronics onto 3D objects. Here, a technique is reported to utilize shape-memory polymers together with carbon nanotube flexible electronics to achieve this goal. Temperature-assisted shape control of these freestanding electronics in a programmable manner is demonstrated, with theoretical analysis for understanding the shape evolution. The shape control process can be executed with prepatterned heaters, desirable for 3D shape formation in an enclosed environment. The incorporation of carbon nanotube transistors, gas sensors, temperature sensors, and memory devices that are capable of self-wrapping onto any irregular shaped-objects without degradations in device performance is demonstrated.

  View details for DOI 10.1002/advs.201500103

  View details for Web of Science ID 000368998500004

  View details for PubMedCentralID PMC5115380

• A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing. Nature communications Chou, H. H., Nguyen, A., Chortos, A., To, J. W., Lu, C., Mei, J., Kurosawa, T., Bae, W. G., Tok, J. B., Bao, Z. 2015; 6: 8011

  Abstract

  Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin's colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control. This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.

  View details for DOI 10.1038/ncomms9011

  View details for PubMedID 26300307

  View details for PubMedCentralID PMC4560774

• A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing NATURE COMMUNICATIONS Chou, H., Nguyen, A., Chortos, A., To, J. W., Lu, C., Mei, J., Kurosawa, T., Bae, W., Tok, J. B., Bao, Z. 2015; 6

  Abstract

  Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin's colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control. This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.

  View details for DOI 10.1038/ncomms9011

  View details for Web of Science ID 000360351600003

  View details for PubMedCentralID PMC4560774

• Flow-enhanced solution printing of all-polymer solar cells NATURE COMMUNICATIONS Diao, Y., Zhou, Y., Kurosawa, T., Shaw, L., Wang, C., Park, S., Guo, Y., Reinspach, J. A., Gu, K., Gu, X., Tee, B. C., Pang, C., Yan, H., Zhao, D., Toney, M. F., Mannsfeld, S. C., Bao, Z. 2015; 6

  Abstract

  Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

  View details for DOI 10.1038/ncomms8955

  View details for Web of Science ID 000360346700010

  View details for PubMedCentralID PMC4557117

• n-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions. Chemistry (Weinheim an der Bergstrasse, Germany) Zhang, S., Naab, B. D., Jucov, E. V., Parkin, S., Evans, E. G., Millhauser, G. L., Timofeeva, T. V., Risko, C., Brédas, J., Bao, Z., Barlow, S., Marder, S. R. 2015; 21 (30): 10878-10885

  Abstract

  Dimers of 2-substituted N,N'-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer CC bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2 , yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2 ) dissociation and of D2 -to-A electron transfer, D2 reacts with A to form D(+) and A(-) by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D(+) /0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. -1.9 V vs. FeCp2 (+/0) ) (Cp=cyclopentadienyl) due to cancelation of trends in the D(+/0) potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed.

  View details for DOI 10.1002/chem.201500611

  View details for PubMedID 26088609

  View details for PubMedCentralID PMC4529998

• Diketopyrrolopyrrole (DPP)-Based Donor-Acceptor Polymers for Selective Dispersion of Large-Diameter Semiconducting Carbon Nanotubes SMALL Lei, T., Lai, Y., Hong, G., Wang, H., Hayoz, P., Weitz, R. T., Chen, C., Dai, H., Bao, Z. 2015; 11 (24): 2946-2954

  Abstract

  Low-bandgap diketopyrrolopyrrole (DPP)-based polymers are used for the selective dispersion of semiconducting single-walled carbon nanotubes (s-SWCNTs). Through rational molecular design to tune the polymer-SWCNT interactions, highly selective dispersions of s-SWCNTs with diameters mainly around 1.5 nm are achieved. The influences of the polymer alkyl side-chain substitution (i.e., branched vs linear side chains) on the dispersing yield and selectivity of s-SWCNTs are investigated. Introducing linear alkyl side chains allows increased polymer-SWCNT interactions through close π-π stacking and improved C-H-π interactions. This work demonstrates that polymer side-chain engineering is an effective method to modulate the polymer-SWCNT interactions and thereby affecting both critical parameters in dispersing yield and selectivity. Using these sorted s-SWCNTs, high-performance SWCNT network thin-film transistors are fabricated. The solution-deposited s-SWCNT transistors yield simultaneously high mobilities of 41.2 cm(2) V(-1) s(-1) and high on/off ratios of greater than 10(4) . In summary, low-bandgap DPP donor-acceptor polymers are a promising class of polymers for selective dispersion of large-diameter s-SWCNTs.

  View details for DOI 10.1002/smll.201403761

  View details for PubMedID 25711378

• Effect of Spacer Length of Siloxane-Terminated Side Chains on Charge Transport in Isoindigo-Based Polymer Semiconductor Thin Films ADVANCED FUNCTIONAL MATERIALS Mei, J., Wu, H., Diao, Y., Appleton, A., Wang, H., Zhou, Y., Lee, W., Kurosawa, T., Chen, W., Bao, Z. 2015; 25 (23): 3455-3462

  View details for DOI 10.1002/adfm.201500684

  View details for Web of Science ID 000356376600002

• Tuning Local Molecular Orientation-Composition Correlations in Binary Organic Thin Films by Solution Shearing ADVANCED FUNCTIONAL MATERIALS Ma, W., Reinspach, J., Zhou, Y., Diao, Y., McAfee, T., Mannsfeld, S. C., Bao, Z., Ade, H. 2015; 25 (21): 3131-3137

  View details for DOI 10.1002/adfm.201500468

  View details for Web of Science ID 000355635300003

• Structural and Electrical Investigation of C-60-Graphene Vertical Heterostructures ACS NANO Kim, K., Lee, T. H., Santos, E. J., Jo, P. S., Salleo, A., Nishi, Y., Bao, Z. 2015; 9 (6): 5922-5928

  Abstract

  Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C60 thin film on graphene. The assembled film structure of C60 on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C60 film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C60 crystal and graphene lattice directions are found, and van der Waals ab initio calculations support the observed phenomena. Moreover, using C60-graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10(3). Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications.

  View details for DOI 10.1021/acsnano.5b00581

  View details for Web of Science ID 000356988500032

  View details for PubMedID 26027690

• Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework ACS CENTRAL SCIENCE To, J. W., Chen, Z., Yao, H., He, J., Kim, K., Chou, H., Pan, L., Wilcox, J., Cui, Y., Bao, Z. 2015; 1 (2): 68-76

  Abstract

  Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 °C with record-high surface area (4073 m(2) g(-1)), large pore volume (2.26 cm(-3)), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.

  View details for DOI 10.1021/acscentsci.5b00149

  View details for Web of Science ID 000365966800007

  View details for PubMedCentralID PMC4827563

• Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework. ACS central science To, J. W., Chen, Z., Yao, H., He, J., Kim, K., Chou, H. H., Pan, L., Wilcox, J., Cui, Y., Bao, Z. 2015; 1 (2): 68-76

  Abstract

  Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 °C with record-high surface area (4073 m(2) g(-1)), large pore volume (2.26 cm(-3)), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.

  View details for DOI 10.1021/acscentsci.5b00149

  View details for PubMedID 27162953

  View details for PubMedCentralID PMC4827563

• Bulky End-Capped [1]Benzothieno[3,2-b]benzothiophenes: Reaching High-Mobility Organic Semiconductors by Fine Tuning of the Crystalline Solid-State Order ADVANCED MATERIALS Schweicher, G., Lemaur, V., Niebel, C., Ruzie, C., Diao, Y., Goto, O., Lee, W., Kim, Y., Arlin, J., Karpinska, J., Kennedy, A. R., Parkin, S. R., Olivier, Y., Mannsfeld, S. C., Cornil, J., Geerts, Y. H., Bao, Z. 2015; 27 (19): 3066-3072

  Abstract

  A series of bulky end-capped [1]benzothieno[3,2-b]benzothiophenes (BTBTs) are developed in order to tune the packing structure via terminal substitution. A coupled theoretical and experimental study allows us to identify 2,7-di-tert-butylBTBT as a new high-performance organic semiconductor with large and well-balanced transfer integrals, as evidenced by quantum-chemical calculations. Single-crystal field-effect transistors show a remarkable average saturation mobility of 7.1 cm(2) V(-1) s(-1) .

  View details for DOI 10.1002/adma.201500322

  View details for Web of Science ID 000354487700016

  View details for PubMedID 25855909

• Epitaxially Grown Strained Pentacene Thin Film on Graphene Membrane SMALL Kim, K., Santos, E. J., Lee, T. H., Nishi, Y., Bao, Z. 2015; 11 (17): 2037-2043

  Abstract

  Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.

  View details for DOI 10.1002/smll.201403006

  View details for PubMedID 25565340

• Large-area formation of self-aligned crystalline domains of organic semiconductors on transistor channels using CONNECT PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Park, S., Giri, G., Shaw, L., Pitner, G., Ha, J., Koo, J. H., Gu, X., Park, J., Lee, T. H., Nam, J. H., Hong, Y., Bao, Z. 2015; 112 (18): 5561-5566

  Abstract

  The electronic properties of solution-processable small-molecule organic semiconductors (OSCs) have rapidly improved in recent years, rendering them highly promising for various low-cost large-area electronic applications. However, practical applications of organic electronics require patterned and precisely registered OSC films within the transistor channel region with uniform electrical properties over a large area, a task that remains a significant challenge. Here, we present a technique termed "controlled OSC nucleation and extension for circuits" (CONNECT), which uses differential surface energy and solution shearing to simultaneously generate patterned and precisely registered OSC thin films within the channel region and with aligned crystalline domains, resulting in low device-to-device variability. We have fabricated transistor density as high as 840 dpi, with a yield of 99%. We have successfully built various logic gates and a 2-bit half-adder circuit, demonstrating the practical applicability of our technique for large-scale circuit fabrication.

  View details for DOI 10.1073/pnas.1419771112

  View details for Web of Science ID 000353953800030

  View details for PubMedID 25902502

  View details for PubMedCentralID PMC4426406

• High performance top contact fused thiophene-diketopyrrolopyrrole copolymer transistors using a photolithographic metal lift-off process ORGANIC ELECTRONICS Xie, Y., Ouyang, S., Wang, D., Lee, W., Bao, Z., Matthews, J. R., Niu, W., Bellman, R. A., He, M., Fong, H. H. 2015; 20: 55-62

  View details for DOI 10.1016/j.orgel.2015.01.002

  View details for Web of Science ID 000351638600009

• Large-Area Assembly of Densely Aligned Single-Walled Carbon Nanotubes Using Solution Shearing and Their Application to Field-Effect Transistors ADVANCED MATERIALS Park, S., Pitner, G., Giri, G., Koo, J. H., Park, J., Kim, K., Wang, H., Sinclair, R., Wong, H. P., Bao, Z. 2015; 27 (16): 2656-2662

  Abstract

  Dense alignment of single-walled carbon nanotubes over a large area is demonstrated using a novel solution-shearing technique. A density of 150-200 single-walled carbon nanotubes per micro-meter is achieved with a current density of 10.08 μA μm(-1) at VDS = -1 V. The on-current density is improved by a factor of 45 over that of random-network single-walled carbon nanotubes.

  View details for DOI 10.1002/adma.201405289

  View details for PubMedID 25788393

• High-Areal-Capacity Silicon Electrodes with Low-Cost Silicon Particles Based on Spatial Control of Self-Healing Binder ADVANCED ENERGY MATERIALS Chen, Z., Wang, C., Lopez, J., Lu, Z., Cui, Y., Bao, Z. 2015; 5 (8)

  View details for DOI 10.1002/aenm.201401826

  View details for Web of Science ID 000353357600005

• Effect of Solution Shearing Method on Packing and Disorder of Organic Semiconductor Polymers CHEMISTRY OF MATERIALS Giri, G., Delongchamp, D. M., Reinspach, J., Fischer, D. A., Richter, L. J., Xu, J., Benight, S., Ayzner, A., He, M., Fang, L., Xue, G., Toney, M. F., Bao, Z. 2015; 27 (7): 2350-2359

  View details for DOI 10.1021/cm503780u

  View details for Web of Science ID 000353176100013

• H-Bonded Supramolecular Polymer for the Selective Dispersion and Subsequent Release of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Pochorovski, I., Wang, H., Feldblyum, J. I., Zhang, X., Antaris, A. L., Bao, Z. 2015; 137 (13): 4328-4331

  Abstract

  Semiconducting, single-walled carbon nanotubes (SWNTs) are promising candidates for applications in thin-film transistors, solar cells, and biological imaging. To harness their full potential, however, it is necessary to separate the semiconducting from the metallic SWNTs present in the as-synthesized SWNT mixture. While various polymers are able to selectively disperse semiconducting SWNTs, the subsequent removal of the polymer is challenging. However, many applications require semiconducting SWNTs in their pure form. Toward this goal, we have designed a 2-ureido-6[1H]-pyrimidinone (UPy)-based H-bonded supramolecular polymer that can selectively disperse semiconducting SWNTs. The dispersion purity is inversely related to the dispersion yield. In contrast to conventional polymers, the polymer described herein was shown to disassemble into monomeric units upon addition of an H-bond-disrupting agent, enabling isolation of dispersant-free, semiconducting SWNTs.

  View details for DOI 10.1021/jacs.5b01704

  View details for PubMedID 25815604

• N-Type Conjugated Polymer-Enabled Selective Dispersion of Semiconducting Carbon Nanotubes for Flexible CMOS-Like Circuits ADVANCED FUNCTIONAL MATERIALS Wang, H., Li, Y., Jimenez-Oses, G., Liu, P., Fang, Y., Zhang, J., Lai, Y., Park, S., Chen, L., Houk, K. N., Bao, Z. 2015; 25 (12): 1837-1844

  View details for DOI 10.1002/adfm.201404126

  View details for Web of Science ID 000351683200015

• Enhancement of ambipolar characteristics in single-walled carbon nanotubes using C-60 and fabrication of logic gates APPLIED PHYSICS LETTERS Park, S., Nam, J. H., Koo, J. H., Lei, T., Bao, Z. 2015; 106 (10)

  View details for DOI 10.1063/1.4914476

  View details for Web of Science ID 000351397600059

• Thermotropic Phase Transition of Benzodithiophene Copolymer Thin Films and Its Impact on Electrical and Photovoltaic Characteristics CHEMISTRY OF MATERIALS Ko, S., Kim, D. H., Ayzner, A. L., Mannsfeld, S. C., Verploegen, E., Nardes, A. M., Kopidakis, N., Toney, M. F., Bao, Z. 2015; 27 (4): 1223-1232

  View details for DOI 10.1021/cm503773j

  View details for Web of Science ID 000350192500013

• Highly skin-conformal microhairy sensor for pulse signal amplification. Advanced materials Pang, C., Koo, J. H., Nguyen, A., Caves, J. M., Kim, M., Chortos, A., Kim, K., Wang, P. J., Tok, J. B., Bao, Z. 2015; 27 (4): 634-640

  Abstract

  A bioinspired microhairy sensor is developed to enable ultraconformability on nonflat surfaces and significant enhancement in the signal-to-noise ratio of the retrieved signals. The device shows ≈12 times increase in the signal-to-noise ratio in the generated capacitive signals, allowing the ultraconformal microhair pressure sensors to be capable of measuring weak pulsations of internal jugular venous pulses stemming from a human neck.

  View details for DOI 10.1002/adma.201403807

  View details for PubMedID 25358966

• Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation. The journal of physical chemistry letters Ayzner, A. L., Nordlund, D., Kim, D. H., Bao, Z., Toney, M. F. 2015; 6 (1): 6-12

  Abstract

  Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.

  View details for DOI 10.1021/jz502253r

  View details for PubMedID 26263084

• An imaging and analysis toolset for the study of Caenorhabditis elegans neurodevelopment Conference on Optical Methods in Developmental Biology III Christensen, R., Bokinsky, A., Santella, A., Wu, Y., Marquina, J., Kovacevic, I., Kumar, A., Winter, P., McCreedy, E., Mohler, W., Bao, Z., Colon-Ramos, D., Shroff, H. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2082394

  View details for Web of Science ID 000353408400003

• Themed issue on "Organic field-effect transistors: interfacial phenomena and electronic properties'' PHYSICAL CHEMISTRY CHEMICAL PHYSICS Krishnamoorthy, K., Facchetti, A. F., Hu, W., Bao, Z. 2015; 17 (40): 26509-26511

  View details for DOI 10.1039/c5cp90162f

  View details for Web of Science ID 000362679300001

  View details for PubMedID 26412332

• Fully biodegradable pressure sensor, viscoelastic behavior of PGS dielectric elastomer upon degradation Boutry, C. M., Amanda Nguyen, Lawal, Q., Chortos, A., Bao, Z., IEEE IEEE. 2015: 1893-1896

  View details for Web of Science ID 000380440800495

• High performance all polymer solar cells fabricated via non-halogenated solvents Zhou, Y., Bao, Z., Kafafi, Z. H., Lane, P. A., Samuel, I. D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2187663

  View details for Web of Science ID 000365813100018

• Efficient Metallic Carbon Nanotube Removal for Highly-Scaled Technologies Shulaker, M. M., Hills, G., Wu, T. F., Bao, Z., Wong, H., Mitra, S., IEEE IEEE. 2015

  View details for Web of Science ID 000380472500209

• Thienoacene dimers based on the thieno[3,2-b] thiophene moiety: synthesis, characterization and electronic properties JOURNAL OF MATERIALS CHEMISTRY C Niebel, C., Kim, Y., Ruzie, C., Karpinska, J., Chattopadhyay, B., Schweicher, G., Richard, A., Lemaur, V., Olivier, Y., Cornil, J., Kennedy, A. R., Diao, Y., Lee, W., Mannsfeld, S., Bao, Z., Geerts, Y. H. 2015; 3 (3): 674-685

  View details for DOI 10.1039/c4tc02158d

  View details for Web of Science ID 000346569700024

• Highly skin-conformal microhairy sensor for pulse signal amplification. Advanced materials Pang, C., Koo, J. H., Nguyen, A., Caves, J. M., Kim, M., Chortos, A., Kim, K., Wang, P. J., Tok, J. B., Bao, Z. 2015; 27 (4): 634-640

  View details for DOI 10.1002/adma.201403807

  View details for PubMedID 25358966

• Flow-enhanced solution printing of all-polymer solar cells. Nature communications Diao, Y., Zhou, Y., Kurosawa, T., Shaw, L., Wang, C., Park, S., Guo, Y., Reinspach, J. A., Gu, K., Gu, X., Tee, B. C., Pang, C., Yan, H., Zhao, D., Toney, M. F., Mannsfeld, S. C., Bao, Z. 2015; 6: 7955-?

  Abstract

  Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

  View details for DOI 10.1038/ncomms8955

  View details for PubMedID 26264528

• Few-layer, large-area, 2D covalent organic framework semiconductor thin films CHEMICAL COMMUNICATIONS Feldblyum, J. I., McCreery, C. H., Andrews, S. C., Kurosawa, T., Santos, E. J., Duong, V., Fang, L., Ayzner, A. L., Bao, Z. 2015; 51 (73): 13894-13897

  Abstract

  In this work, we synthesize large-area thin films of a conjugated, imine-based, two-dimensional covalent organic framework at the solution/air interface. Thicknesses between ∼2-200 nm are achieved. Films can be transferred to any desired substrate by lifting from underneath, enabling their use as the semiconducting active layer in field-effect transistors.

  View details for DOI 10.1039/c5cc04679c

  View details for Web of Science ID 000360398900006

• Solvent effects on polymer sorting of carbon nanotubes with applications in printed electronics. Small Wang, H., Hsieh, B., Jiménez-Osés, G., Liu, P., Tassone, C. J., Diao, Y., Lei, T., Houk, K. N., Bao, Z. 2015; 11 (1): 126-133

  Abstract

  Regioregular poly(3-alkylthiophene) (P3AT) polymers have been previously reported for the selective, high-yield dispersion of semiconducting single-walled carbon nanotubes (SWCNTs) in toluene. Here, five alternative solvents are investigated, namely, tetrahydrofuran, decalin, tetralin, m-xylene, and o-xylene, for the dispersion of SWCNTs by poly(3-dodecylthiophene) P3DDT. The dispersion yield could be increased to over 40% using decalin or o-xylene as the solvents while maintaining high selectivity towards semiconducting SWCNTs. Molecular dynamics (MD) simulations in explicit solvents are used to explain the improved sorting yield. In addition, a general mechanism is proposed to explain the selective dispersion of semiconducting SWCNTs by conjugated polymers. The possibility to perform selective sorting of semiconducting SWCNTs using various solvents provides a greater diversity of semiconducting SWCNT ink properties, such as boiling point, viscosity, and surface tension as well as toxicity. The efficacy of these new semiconducting SWCNT inks is demonstrated by using the high boiling point and high viscosity solvent tetralin for inkjet-printed transistors, where solvent properties are more compatible with the inkjet printing head and improved droplet formation.

  View details for DOI 10.1002/smll.201401890

  View details for PubMedID 25138541

• Significant enhancement of infrared photodetector sensitivity using a semiconducting single-walled carbon nanotube/c60 phototransistor. Advanced materials Park, S., Kim, S. J., Nam, J. H., Pitner, G., Lee, T. H., Ayzner, A. L., Wang, H., Fong, S. W., Vosgueritchian, M., Park, Y. J., Brongersma, M. L., Bao, Z. 2015; 27 (4): 759-765

  Abstract

  A highly sensitive single-walled carbon nanotube/C60 -based infrared photo-transistor is fabricated with a responsivity of 97.5 A W(-1) and detectivity of 1.17 × 10(9) Jones at 1 kHz under a source/drain bias of -0.5 V. The much improved performance is enabled by this unique device architecture that enables a high photoconductive gain of ≈10(4) with a response time of several milliseconds.

  View details for DOI 10.1002/adma.201404544

  View details for PubMedID 25607919

• Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation JOURNAL OF PHYSICAL CHEMISTRY LETTERS Ayzner, A. L., Nordlund, D., Kim, D., Bao, Z., Toney, M. F. 2015; 6 (1): 6-12

  Abstract

  Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.

  View details for DOI 10.1021/jz502253r

  View details for Web of Science ID 000347513700002

• Understanding Polymorphism in Organic Semiconductor Thin Films through Nanoconfinement JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Diao, Y., Lenn, K. M., Lee, W., Blood-Forsythe, M. A., Xu, J., Mao, Y., Kim, Y., Reinspach, J. A., Park, S., Aspuru-Guzik, A., Xue, G., Clancy, P., Bao, Z., Mannsfeld, S. C. 2014; 136 (49): 17046-17057

  Abstract

  Understanding crystal polymorphism is a long-standing challenge relevant to many fields, such as pharmaceuticals, organic semiconductors, pigments, food, and explosives. Controlling polymorphism of organic semiconductors (OSCs) in thin films is particularly important given that such films form the active layer in most organic electronics devices and that dramatic changes in the electronic properties can be induced even by small changes in the molecular packing. However, there are very few polymorphic OSCs for which the structure-property relationships have been elucidated so far. The major challenges lie in the transient nature of metastable forms and the preparation of phase-pure, highly crystalline thin films for resolving the crystal structures and evaluating the charge transport properties. Here we demonstrate that the nanoconfinement effect combined with the flow-enhanced crystal engineering technique is a powerful and likely material-agnostic method to identify existing polymorphs in OSC materials and to prepare the individual pure forms in thin films at ambient conditions. With this method we prepared high quality crystal polymorphs and resolved crystal structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), including a new polymorph discovered via in situ grazing incidence X-ray diffraction and confirmed by molecular mechanic simulations. We further correlated molecular packing with charge transport properties using quantum chemical calculations and charge carrier mobility measurements. In addition, we applied our methodology to a [1]benzothieno[3,2-b][1]1benzothiophene (BTBT) derivative and successfully stabilized its metastable form.

  View details for DOI 10.1021/ja507179d

  View details for Web of Science ID 000346544200021

  View details for PubMedID 25333565

• Large-Scale Production of Graphene Nanoribbons from Electrospun Polymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, N., Kim, K., Hsu, P., Sokolov, A. N., Yap, F. L., Yuan, H., Xie, Y., Yan, H., Cui, Y., Hwang, H. Y., Bao, Z. 2014; 136 (49): 17284-17291

  Abstract

  Graphene nanoribbons (GNRs) are promising building blocks for high-performance electronics due to their high electron mobility and dimensionality-induced bandgap. Despite many past efforts, direct synthesis of GNRs with controlled dimensions and scalability remains challenging. Here we report the scalable synthesis of GNRs using electrospun polymer nanofiber templates. Palladium-incorporated poly(4-vinylphenol) nanofibers were prepared by electrospinning with controlled diameter and orientation. Highly graphitized GNRs as narrow as 10 nm were then synthesized from these templates by chemical vapor deposition. A transport gap can be observed in 30 nm-wide GNRs, enabling them to function as field-effect transistors at room temperature. Our results represent the first success on the scalable synthesis of highly graphitized GNRs from polymer templates. Furthermore, the generality of this method allows various polymers to be explored, which will lead to understanding of growth mechanism and rational control over crystallinity, feature size and bandgap to enable a new pathway for graphene electronics.

  View details for DOI 10.1021/ja509871n

  View details for PubMedID 25407608

• Selective solution shearing deposition of high performance TIPS-pentacene polymorphs through chemical patterning JOURNAL OF MATERIALS RESEARCH Giri, G., Miller, E., Bao, Z. 2014; 29 (22): 2615-2624

  View details for DOI 10.1557/jmr.2014.305

  View details for Web of Science ID 000346429500002

• Stretchable Energy-Harvesting Tactile Electronic Skin Capable of Differentiating Multiple Mechanical Stimuli Modes ADVANCED MATERIALS Park, S., Kim, H., Vosgueritchian, M., Cheon, S., Kim, H., Koo, J. H., Kim, T. R., Lee, S., Schwartz, G., Chang, H., Bao, Z. 2014; 26 (43): 7324-7332

  Abstract

  The first stretchable energy-harvesting electronic-skin device capable of differentiating and generating energy from various mechanical stimuli, such as normal pressure, lateral strain, bending, and vibration, is presented. A pressure sensitivity of 0.7 kPa(-1) is achieved in the pressure region <1 kPa with power generation of tens of μW cm(-2) from a gentle finger touch.

  View details for DOI 10.1002/adma.201402574

  View details for Web of Science ID 000345223600006

• Stretchable energy-harvesting tactile electronic skin capable of differentiating multiple mechanical stimuli modes. Advanced materials Park, S., Kim, H., Vosgueritchian, M., Cheon, S., Kim, H., Koo, J. H., Kim, T. R., Lee, S., Schwartz, G., Chang, H., Bao, Z. 2014; 26 (43): 7324-7332

  Abstract

  The first stretchable energy-harvesting electronic-skin device capable of differentiating and generating energy from various mechanical stimuli, such as normal pressure, lateral strain, bending, and vibration, is presented. A pressure sensitivity of 0.7 kPa(-1) is achieved in the pressure region <1 kPa with power generation of tens of μW cm(-2) from a gentle finger touch.

  View details for DOI 10.1002/adma.201402574

  View details for PubMedID 25256696

• Self-Assembled Monolayers of Cyclohexyl-Terminated Phosphonic Acids as a General Dielectric Surface for High-Performance Organic Thin-Film Transistors ADVANCED MATERIALS Liu, D., He, Z., Su, Y., Diao, Y., Mannsfeld, S. C., Bao, Z., Xu, J., Miao, Q. 2014; 26 (42): 7190-7196

  Abstract

  A novel self-assembled monolayer (SAM) on AlOy /TiOx is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlOy /TiOx functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm(2) V(-1) s(-1) for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors.

  View details for DOI 10.1002/adma.201402822

  View details for Web of Science ID 000344783300006

• Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care NATURE COMMUNICATIONS Chen, L. Y., Tee, B. C., Chortos, A. L., Schwartz, G., Tse, V., Lipomi, D. J., Wong, H. P., McConnell, M. V., Bao, Z. 2014; 5

  Abstract

  Continuous monitoring of internal physiological parameters is essential for critical care patients, but currently can only be practically achieved via tethered solutions. Here we report a wireless, real-time pressure monitoring system with passive, flexible, millimetre-scale sensors, scaled down to unprecedented dimensions of 1 × 1 × 0.1 cubic millimeters. This level of dimensional scaling is enabled by novel sensor design and detection schemes, which overcome the operating frequency limits of traditional strategies and exhibit insensitivity to lossy tissue environments. We demonstrate the use of this system to capture human pulse waveforms wirelessly in real time as well as to monitor in vivo intracranial pressure continuously in proof-of-concept mice studies using sensors down to 2.5 × 2.5 × 0.1 cubic millimeters. We further introduce printable wireless sensor arrays and show their use in real-time spatial pressure mapping. Looking forward, this technology has broader applications in continuous wireless monitoring of multiple physiological parameters for biomedical research and patient care.

  View details for DOI 10.1038/ncomms6028

  View details for Web of Science ID 000343935600001

• Polypyrrole/Agarose-Based Electronically Conductive and Reversibly Restorable Hydrogel ACS NANO Hur, J., Im, K., Kim, S. W., Kim, J., Chung, D., Kim, T., Jo, K. H., Hahn, J. H., Bao, Z., Hwang, S., Park, N. 2014; 8 (10): 10066-10076

  Abstract

  Conductive hydrogels are a class of composite materials that consist of hydrated and conducting polymers. Due to the mechanical similarity to biointerfaces such as human skin, conductive hydrogels have been primarily utilized as bioelectrodes, specifically neuroprosthetic electrodes, in an attempt to replace metallic electrodes by enhancing the mechanical properties and long-term stability of the electrodes within living organisms. Here, we report a conductive, smart hydrogel, which is thermoplastic and self-healing owing to its unique properties of reversible liquefaction and gelation in response to thermal stimuli. In addition, we demonstrated that our conductive hydrogel could be utilized to fabricate bendable, stretchable, and patternable electrodes directly on human skin. The excellent mechanical and thermal properties of our hydrogel make it potentially useful in a variety of biomedical applications such as electronic skin.

  View details for DOI 10.1021/nn502704g

  View details for Web of Science ID 000343952600041

• Electronic Readout Enzyme-Linked Immunosorbent Assay with Organic Field-Effect Transistors as a Preeclampsia Prognostic ADVANCED MATERIALS Hammock, M. L., Knopfmacher, O., Ng, T. N., Tok, J. B., Bao, Z. 2014; 26 (35): 6138-?

  Abstract

  Organic field-effect transistor (OFET) sensors can meet the need for portable and real-time diagnostics. An electronicreadout enzyme-linked immunosorbent assay using OFETs for the detection of a panel of three biomarkers in complex media to create a pre-eclampsia prognostic is demonstrated, along with biodetection utilizing a fully inkjet-printed and flexible OFET to underscore our ability to produce disposable devices.

  View details for DOI 10.1002/adma.201401829

  View details for Web of Science ID 000342148600013

  View details for PubMedID 25047764

• Tunable Flexible Pressure Sensors using Microstructured Elastomer Geometries for Intuitive Electronics ADVANCED FUNCTIONAL MATERIALS Tee, B. C., Chortos, A., Dunn, R. R., Schwartz, G., Eason, E., Bao, Z. 2014; 24 (34): 5427-5434

  View details for DOI 10.1002/adfm.201400712

  View details for Web of Science ID 000341834000013

• High performance organic thin film transistors using chemically modified bottom contacts and dielectric surfaces ORGANIC ELECTRONICS Xie, Y., Cai, S., Shi, Q., Ouyang, S., Lee, W., Bao, Z., Matthews, J. R., Bellman, R. A., He, M., Fong, H. H. 2014; 15 (9): 2073-2078

  View details for DOI 10.1016/j.orgel.2014.05.015

  View details for Web of Science ID 000340072200025

• Skin-inspired electronic devices MATERIALS TODAY Chortos, A., Bao, Z. 2014; 17 (7): 321-331

  View details for DOI 10.1016/j.mattod.2014.05.006

  View details for Web of Science ID 000342360600014

• A Three-Dimensionally Interconnected Carbon Nanotube-Conducting Polymer Hydrogel Network for High-Performance Flexible Battery Electrodes ADVANCED ENERGY MATERIALS Chen, Z., To, J. W., Wang, C., Lu, Z., Liu, N., Chortos, A., Pan, L., Wei, F., Cui, Y., Bao, Z. 2014; 4 (12)

  View details for DOI 10.1002/aenm.201400207

  View details for Web of Science ID 000341234600011

• Comparing the Device Physics and Morphology of Polymer Solar Cells Employing Fullerenes and Non-Fullerene Acceptors ADVANCED ENERGY MATERIALS Bloking, J. T., Giovenzana, T., Higgs, A. T., Ponec, A. J., Hoke, E. T., Vandewal, K., Ko, S., Bao, Z., Sellinger, A., McGehee, M. D. 2014; 4 (12)

  View details for DOI 10.1002/aenm.201301426

  View details for Web of Science ID 000341234600001

• A Rapid and Facile Soft Contact Lamination Method: Evaluation of Polymer Semiconductors for Stretchable Transistors CHEMISTRY OF MATERIALS Wu, H., Benight, S. J., Chortos, A., Lee, W., Mei, J., To, J. W., Lu, C., He, M., Tok, J. B., Chen, W., Bao, Z. 2014; 26 (15): 4544-4551

  View details for DOI 10.1021/cm502271j

  View details for Web of Science ID 000340346300029

• Using in-Situ Polymerization of Conductive Polymers to Enhance the Electrical Properties of Solution-Processed Carbon Nanotube Films and Fibers ACS APPLIED MATERIALS & INTERFACES Allen, R., Pan, L., Fuller, G. G., Bao, Z. 2014; 6 (13): 9966-9974

  Abstract

  Single-walled carbon nanotubes/polymer composites typically have limited conductivity due to a low concentration of nanotubes and the insulating nature of the polymers used. Here we combined a method to align carbon nanotubes with in-situ polymerization of conductive polymer to form composite films and fibers. Use of the conducting polymer raised the conductivity of the films by 2 orders of magnitude. On the other hand, CNT fiber formation was made possible with in-situ polymerization to provide more mechanical support to the CNTs from the formed conducting polymer. The carbon nanotube/conductive polymer composite films and fibers had conductivities of 3300 and 170 S/cm, respectively. The relatively high conductivities were attributed to the polymerization process, which doped both the SWNTs and the polymer. In-situ polymerization can be a promising solution-processable method to enhance the conductivity of carbon nanotube films and fibers.

  View details for DOI 10.1021/am5019995

  View details for Web of Science ID 000338979900010

  View details for PubMedID 24914703

• Highly Stable Carbon Nanotube Top-Gate Transistors with Tunable Threshold Voltage ADVANCED MATERIALS Wang, H., Cobb, B., van Breemen, A., Gelinck, G., Bao, Z. 2014; 26 (26): 4588-?

  Abstract

  Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time.

  View details for DOI 10.1002/adma.201400540

  View details for PubMedID 24789423

• Large-area, transparent, and flexible infrared photodetector fabricated using p-N junctions formed by N-doping chemical vapor deposition grown graphene. Nano letters Liu, N., Tian, H., Schwartz, G., Tok, J. B., Ren, T., Bao, Z. 2014; 14 (7): 3702-3708

  Abstract

  Graphene is a highly promising material for high speed, broadband, and multicolor photodetection. Because of its lack of bandgap, individually gated P- and N-regions are needed to fabricate photodetectors. Here we report a technique for making a large-area photodetector on the basis of controllable fabrication of graphene P-N junctions. Our selectively doped chemical vapor deposition (CVD) graphene photodetector showed a ∼5% modulation of conductance under global IR irradiation. By comparing devices of various geometries, we identify that both the homogeneous and the P-N junction regions contribute competitively to the photoresponse. Furthermore, we demonstrate that our two-terminal graphene photodetector can be fabricated on both transparent and flexible substrates without the need for complex fabrication processes used in electrically gated three-terminal devices. This represents the first demonstration of a fully transparent and flexible graphene-based IR photodetector that exhibits both good photoresponsivity and high bending capability. This simple approach should facilitate the development of next generation high-performance IR photodetectors.

  View details for DOI 10.1021/nl500443j

  View details for PubMedID 24927382

• Morphology control strategies for solution-processed organic semiconductor thin films ENERGY & ENVIRONMENTAL SCIENCE Diao, Y., Shaw, L., Bao, Z., Mannsfeld, S. C. 2014; 7 (7): 2145-2159

  View details for DOI 10.1039/c4ee00688g

  View details for Web of Science ID 000337977600005

• Effective Solution- and Vacuum-Processed n-Doping by Dimers of Benzimidazoline Radicals. Advanced materials Naab, B. D., Zhang, S., Vandewal, K., Salleo, A., Barlow, S., Marder, S. R., Bao, Z. 2014; 26 (25): 4268-4272

  View details for DOI 10.1002/adma.201400668

  View details for PubMedID 24753007

• Highly stretchable transistors using a microcracked organic semiconductor. Advanced materials Chortos, A., Lim, J., To, J. W., Vosgueritchian, M., Dusseault, T. J., Kim, T., Hwang, S., Bao, Z. 2014; 26 (25): 4253-4259

  View details for DOI 10.1002/adma.201305462

  View details for PubMedID 24740928

• Effect of Non-Chlorinated Mixed Solvents on Charge Transport and Morphology of Solution-Processed Polymer Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Lee, W., Giri, G., Diao, Y., Tassone, C. J., Matthews, J. R., Sorensen, M. L., Mannsfeld, S. C., Chen, W., Fong, H. H., Tok, J. B., Toney, M. F., He, M., Bao, Z. 2014; 24 (23): 3524-3534

  View details for DOI 10.1002/adfm.201303794

  View details for Web of Science ID 000337484300007

• The Large-Area, Solution-Based Deposition of Single-Crystal Organic Semiconductors ISRAEL JOURNAL OF CHEMISTRY Shaw, L., Bao, Z. 2014; 54 (5-6): 496-512

  View details for DOI 10.1002/ijch.201400032

  View details for Web of Science ID 000338035200007

• High Performance All-Polymer Solar Cell via Polymer Side-Chain Engineering. Advanced materials Zhou, Y., Kurosawa, T., Ma, W., Guo, Y., Fang, L., Vandewal, K., Diao, Y., Wang, C., Yan, Q., Reinspach, J., Mei, J., Appleton, A. L., Koleilat, G. I., Gao, Y., Mannsfeld, S. C., Salleo, A., Ade, H., Zhao, D., Bao, Z. 2014; 26 (22): 3767-3772

  View details for DOI 10.1002/adma.201306242

  View details for PubMedID 24664632

• High performance tetrathienoacene-DDP based polymer thin-film transistors using a photo-patternable epoxy gate insulating layer ORGANIC ELECTRONICS Shi, Q., Xie, Y., Cai, S., Lee, W., Bao, Z., Matthews, J. R., Simonton, K. L., Myers, T. E., Bellman, R. A., He, M., Fong, H. H. 2014; 15 (5): 991-996

  View details for DOI 10.1016/j.orgel.2014.01.022

  View details for Web of Science ID 000334292900004

• VLSI-Compatible Carbon Nanotube Doping Technique with Low Work-Function Metal Oxides. Nano letters Suriyasena Liyanage, L., Xu, X., Pitner, G., Bao, Z., Wong, H. P. 2014; 14 (4): 1884-1890

  Abstract

  Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, as-made carbon nanotube field effect transistors (CNFETs) are p-type in ambient, and a consistent and reproducible n-type carbon nanotube (CNT) doping technique has yet to be realized. In addition, for very large scale integration (VLSI) of CNT transistors, it is imperative to use a solid-state method that can be applied on the wafer scale. Herein we present a novel, VLSI-compatible doping technique to fabricate n-type CNT transistors using low work-function metal oxides as gate dielectrics. Using this technique we demonstrate wafer-scale, aligned CNT transistors with yttrium oxide (Y2Ox) gate dielectrics that exhibit n-type behavior with Ion/Ioff of 10(6) and inverse subthreshold slope of 95 mV/dec. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses confirm that slow (∼1 Å/s) evaporation of yttrium on the CNTs can form a smooth surface that provides excellent wetting to CNTs. Further analysis of the yttrium oxide gate dielectric using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques revealed that partially oxidized elemental yttrium content increases underneath the surface where it acts as a reducing agent on nanotubes by donating electrons that gives rise to n-type doping in CNTs. We further confirm the mechanism for this technique with other low work-function metals such as lanthanum (La), erbium (Er), and scandium (Sc) which also provide similar CNT NFET behavior after transistor fabrication. This study paves the way to exploiting a wide range of materials for an effective n-type carbon nanotube transistor for a complementary (p- and n-type) transistor technology.

  View details for DOI 10.1021/nl404654j

  View details for PubMedID 24628497

• Tuning the threshold voltage of carbon nanotube transistors by n-type molecular doping for robust and flexible complementary circuits. Proceedings of the National Academy of Sciences of the United States of America Wang, H., Wei, P., Li, Y., Han, J., Lee, H. R., Naab, B. D., Liu, N., Wang, C., Adijanto, E., Tee, B. C., Morishita, S., Li, Q., Gao, Y., Cui, Y., Bao, Z. 2014; 111 (13): 4776-4781

  Abstract

  Tuning the threshold voltage of a transistor is crucial for realizing robust digital circuits. For silicon transistors, the threshold voltage can be accurately controlled by doping. However, it remains challenging to tune the threshold voltage of single-wall nanotube (SWNT) thin-film transistors. Here, we report a facile method to controllably n-dope SWNTs using 1H-benzoimidazole derivatives processed via either solution coating or vacuum deposition. The threshold voltages of our polythiophene-sorted SWNT thin-film transistors can be tuned accurately and continuously over a wide range. Photoelectron spectroscopy measurements confirmed that the SWNT Fermi level shifted to the conduction band edge with increasing doping concentration. Using this doping approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants. We observed an unprecedented noise margin of 28 V at VDD = 80 V (70% of 1/2VDD) and a gain of 85. Additionally, robust SWNT complementary metal-oxide-semiconductor inverter (noise margin 72% of 1/2VDD) and logic gates with rail-to-rail output voltage swing and subnanowatt power consumption were fabricated onto a highly flexible substrate.

  View details for DOI 10.1073/pnas.1320045111

  View details for PubMedID 24639537

• VLSI-Compatible Carbon Nanotube Doping Technique with Low Work-Function Metal Oxides NANO LETTERS Liyanage, L., Xu, X., Pitner, G., Bao, Z., Wong, H. 2014; 14 (4): 1884-1890

  View details for DOI 10.1021/nl404654j

  View details for Web of Science ID 000334572400031

• High-yield sorting of small-diameter carbon nanotubes for solar cells and transistors. ACS nano Wang, H., Koleilat, G. I., Liu, P., Jiménez-Osés, G., Lai, Y., Vosgueritchian, M., Fang, Y., Park, S., Houk, K. N., Bao, Z. 2014; 8 (3): 2609-2617

  Abstract

  We describe herein a high-yield method to selectively disperse semiconducting CoMoCAT (CO disproportionation on Co-Mo catalysts) single-walled carbon nanotubes (SWNTs) with regioregular poly(3-alkylthiophenes) polymers. We observed that the dispersion yield was directly related to the length of the polymer's alkyl side chains. Molecular dynamics simulations in explicit toluene (real toluene molecules) indicate that polythiophenes with longer alkyl side chains bind strongly to SWNTs, due to the increased overall surface contact area with the nanotube. Furthermore, the sorting process selectively enriches smaller-diameter CoMoCAT SWNTs with larger bandgaps, which is ideal for solar cell applications. Compared to the larger diameter sorted HiPco (High-Pressure CO) SWNTs, solar cells fabricated using our sorted CoMoCAT SWNTs demonstrated higher open-circuit voltage (Voc) and infrared external quantum efficiency (EQE). The Voc achieved is the highest reported for solar cells based on SWNT absorbers under simulated AM1.5 solar illumination. Additionally, we employed the sorted CoMoCAT SWNTs to fabricate thin film transistors with excellent uniformity and device performance.

  View details for DOI 10.1021/nn406256y

  View details for PubMedID 24484388

• Semiconducting polymer nanoparticles as photoacoustic molecular imaging probes in living mice. Nature nanotechnology Pu, K., Shuhendler, A. J., Jokerst, J. V., Mei, J., Gambhir, S. S., Bao, Z., Rao, J. 2014; 9 (3): 233-239

  Abstract

  Photoacoustic imaging holds great promise for the visualization of physiology and pathology at the molecular level with deep tissue penetration and fine spatial resolution. To fully utilize this potential, photoacoustic molecular imaging probes have to be developed. Here, we introduce near-infrared light absorbing semiconducting polymer nanoparticles as a new class of contrast agents for photoacoustic molecular imaging. These nanoparticles can produce a stronger signal than the commonly used single-walled carbon nanotubes and gold nanorods on a per mass basis, permitting whole-body lymph-node photoacoustic mapping in living mice at a low systemic injection mass. Furthermore, the semiconducting polymer nanoparticles possess high structural flexibility, narrow photoacoustic spectral profiles and strong resistance to photodegradation and oxidation, enabling the development of the first near-infrared ratiometric photoacoustic probe for in vivo real-time imaging of reactive oxygen species-vital chemical mediators of many diseases. These results demonstrate semiconducting polymer nanoparticles to be an ideal nanoplatform for developing photoacoustic molecular probes.

  View details for DOI 10.1038/nnano.2013.302

  View details for PubMedID 24463363

  View details for PubMedCentralID PMC3947658

• Sequentially solution-processed, nanostructured polymer photovoltaics using selective solvents ENERGY & ENVIRONMENTAL SCIENCE Kim, D. H., Mei, J., Ayzner, A. L., Schmidt, K., Giri, G., Appleton, A. L., Toney, M. F., Bao, Z. 2014; 7 (3): 1103-1109

  View details for DOI 10.1039/c3ee43541e

  View details for Web of Science ID 000333203900028

• Lead candidates for high-performance organic photovoltaics from high-throughput quantum chemistry - the Harvard Clean Energy Project ENERGY & ENVIRONMENTAL SCIENCE Hachmann, J., Olivares-Amaya, R., Jinich, A., Appleton, A. L., Blood-Forsythe, M. A., Seress, L. R., Roman-Salgado, C., Trepte, K., Atahan-Evrenk, S., Er, S., Shrestha, S., Mondal, R., Sokolov, A., Bao, Z., Aspuru-Guzik, A. 2014; 7 (2): 698-704

  View details for DOI 10.1039/c3ee42756k

  View details for Web of Science ID 000331413700023

• A flexible bimodal sensor array for simultaneous sensing of pressure and temperature. Advanced materials Tien, N. T., Jeon, S., Kim, D., Trung, T. Q., Jang, M., Hwang, B., Byun, K., Bae, J., Lee, E., Tok, J. B., Bao, Z., Lee, N., Park, J. 2014; 26 (5): 796-804

  Abstract

  Diverse signals generated from the sensing elements embedded in flexible electronic skins (e-skins) are typically interfered by strain energy generated through processes such as touching, bending, stretching or twisting. Herein, we demonstrate a flexible bimodal sensor that can separate a target signal from the signal by mechanical strain through the integration of a multi-stimuli responsive gate dielectric and semiconductor channel into the single field-effect transistor (FET) platform.

  View details for DOI 10.1002/adma.201302869

  View details for PubMedID 24493054

• Ultrafast energy transfer from rigid, branched side-chains into a conjugated, alternating copolymer JOURNAL OF CHEMICAL PHYSICS Griffin, G. B., Lundin, P. M., Rolczynski, B. S., Linkin, A., McGillicuddy, R. D., Bao, Z., Engel, G. S. 2014; 140 (3)

  Abstract

  We present the synthesis and characterization of a benzodithiophene/thiophene alternating copolymer decorated with rigid, singly branched pendant side chains. We characterize exciton migration and recombination dynamics in these molecules in tetrahydrofuran solution, using a combination of static and time-resolved spectroscopies. As control experiments, we also measure electronic relaxation dynamics in isolated molecular analogues of both the side chain and polymer moieties. We employ semi-empirical and time-dependent density functional theory calculations to show that photoexcitation of the decorated copolymer using 395 nm laser pulses results in excited states primarily localized on the pendant side chains. We use ultrafast transient absorption spectroscopy to show that excitations are transferred to the polymer backbone faster than the instrumental response function, ∼250 fs.

  View details for DOI 10.1063/1.4855156

  View details for Web of Science ID 000330614400056

  View details for PubMedCentralID PMC3977892

• Ultrafast energy transfer from rigid, branched side-chains into a conjugated, alternating copolymer. journal of chemical physics Griffin, G. B., Lundin, P. M., Rolczynski, B. S., Linkin, A., McGillicuddy, R. D., Bao, Z., Engel, G. S. 2014; 140 (3): 034903-?

  Abstract

  We present the synthesis and characterization of a benzodithiophene/thiophene alternating copolymer decorated with rigid, singly branched pendant side chains. We characterize exciton migration and recombination dynamics in these molecules in tetrahydrofuran solution, using a combination of static and time-resolved spectroscopies. As control experiments, we also measure electronic relaxation dynamics in isolated molecular analogues of both the side chain and polymer moieties. We employ semi-empirical and time-dependent density functional theory calculations to show that photoexcitation of the decorated copolymer using 395 nm laser pulses results in excited states primarily localized on the pendant side chains. We use ultrafast transient absorption spectroscopy to show that excitations are transferred to the polymer backbone faster than the instrumental response function, ∼250 fs.

  View details for DOI 10.1063/1.4855156

  View details for PubMedID 25669410

• Side Chain Engineering in Solution-Processable Conjugated Polymers CHEMISTRY OF MATERIALS Mei, J., Bao, Z. 2014; 26 (1): 604-615

  View details for DOI 10.1021/cm4020805

  View details for Web of Science ID 000330416900050

• Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method. Nature communications Yuan, Y., Giri, G., Ayzner, A. L., Zoombelt, A. P., Mannsfeld, S. C., Chen, J., Nordlund, D., Toney, M. F., Huang, J., Bao, Z. 2014; 5: 3005-?

  Abstract

  Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.

  View details for DOI 10.1038/ncomms4005

  View details for PubMedID 24398476

• An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film. Nature communications Pan, L., Chortos, A., Yu, G., Wang, Y., Isaacson, S., Allen, R., Shi, Y., Dauskardt, R., Bao, Z. 2014; 5: 3002-?

  Abstract

  Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

  View details for DOI 10.1038/ncomms4002

  View details for PubMedID 24389734

• Highly stable organic polymer field-effect transistor sensor for selective detection in the marine environment. Nature communications Knopfmacher, O., Hammock, M. L., Appleton, A. L., Schwartz, G., Mei, J., Lei, T., Pei, J., Bao, Z. 2014; 5: 2954-?

  Abstract

  In recent decades, the susceptibility to degradation in both ambient and aqueous environments has prevented organic electronics from gaining rapid traction for sensing applications. Here we report an organic field-effect transistor sensor that overcomes this barrier using a solution-processable isoindigo-based polymer semiconductor. More importantly, these organic field-effect transistor sensors are stable in both freshwater and seawater environments over extended periods of time. The organic field-effect transistor sensors are further capable of selectively sensing heavy-metal ions in seawater. This discovery has potential for inexpensive, ink-jet printed, and large-scale environmental monitoring devices that can be deployed in areas once thought of as beyond the scope of organic materials.

  View details for DOI 10.1038/ncomms3954

  View details for PubMedID 24389531

• Selective metal deposition at graphene line defects by atomic layer deposition. Nature communications Kim, K., Lee, H., Johnson, R. W., Tanskanen, J. T., Liu, N., Kim, M., Pang, C., Ahn, C., Bent, S. F., Bao, Z. 2014; 5: 4781-?

  Abstract

  One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene's line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphene's grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt-graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively.

  View details for DOI 10.1038/ncomms5781

  View details for PubMedID 25179368

• Facile Synthesis of Nitrogen-Doped Porous Carbon for Selective CO2 Capture He, J., To, J., Mei, J., Bao, Z., Wilcox, J., Dixon, T., Herzog, H., Twinning, S. ELSEVIER SCIENCE BV. 2014: 2144-2151

  View details for DOI 10.1016/j.egypro.2014.11.233

  View details for Web of Science ID 000361211502031

• An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film. Nature communications Pan, L., Chortos, A., Yu, G., Wang, Y., Isaacson, S., Allen, R., Shi, Y., Dauskardt, R., Bao, Z. 2014; 5: 3002-?

  Abstract

  Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

  View details for DOI 10.1038/ncomms4002

  View details for PubMedID 24389734

• One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films. Nature communications Giri, G., Li, R., Smilgies, D., Li, E. Q., Diao, Y., Lenn, K. M., Chiu, M., Lin, D. W., Allen, R., Reinspach, J., Mannsfeld, S. C., Thoroddsen, S. T., Clancy, P., Bao, Z., Amassian, A. 2014; 5: 3573-?

  Abstract

  A crystal's structure has significant impact on its resulting biological, physical, optical and electronic properties. In organic electronics, 6,13(bis-triisopropylsilylethynyl)pentacene (TIPS-pentacene), a small-molecule organic semiconductor, adopts metastable polymorphs possessing significantly faster charge transport than the equilibrium crystal when deposited using the solution-shearing method. Here, we use a combination of high-speed polarized optical microscopy, in situ microbeam grazing incidence wide-angle X-ray-scattering and molecular simulations to understand the mechanism behind formation of metastable TIPS-pentacene polymorphs. We observe that thin-film crystallization occurs first at the air-solution interface, and nanoscale vertical spatial confinement of the solution results in formation of metastable polymorphs, a one-dimensional and large-area analogy to crystallization of polymorphs in nanoporous matrices. We demonstrate that metastable polymorphism can be tuned with unprecedented control and produced over large areas by either varying physical confinement conditions or by tuning energetic conditions during crystallization through use of solvent molecules of various sizes.

  View details for DOI 10.1038/ncomms4573

  View details for PubMedID 24736391

• Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care. Nature communications Chen, L. Y., Tee, B. C., Chortos, A. L., Schwartz, G., Tse, V., Lipomi, D. J., Wong, H. P., McConnell, M. V., Bao, Z. 2014; 5: 5028-?

  Abstract

  Continuous monitoring of internal physiological parameters is essential for critical care patients, but currently can only be practically achieved via tethered solutions. Here we report a wireless, real-time pressure monitoring system with passive, flexible, millimetre-scale sensors, scaled down to unprecedented dimensions of 1 × 1 × 0.1 cubic millimeters. This level of dimensional scaling is enabled by novel sensor design and detection schemes, which overcome the operating frequency limits of traditional strategies and exhibit insensitivity to lossy tissue environments. We demonstrate the use of this system to capture human pulse waveforms wirelessly in real time as well as to monitor in vivo intracranial pressure continuously in proof-of-concept mice studies using sensors down to 2.5 × 2.5 × 0.1 cubic millimeters. We further introduce printable wireless sensor arrays and show their use in real-time spatial pressure mapping. Looking forward, this technology has broader applications in continuous wireless monitoring of multiple physiological parameters for biomedical research and patient care.

  View details for DOI 10.1038/ncomms6028

  View details for PubMedID 25284074

• Probing the interfacial molecular packing in TIPS-pentacene organic semiconductors by surface enhanced Raman scattering JOURNAL OF MATERIALS CHEMISTRY C Xu, J., Diao, Y., Zhou, D., Mao, Y., Giri, G., Chen, W., Liu, N., Mannsfeld, S. C., Xue, G., Bao, Z. 2014; 2 (16): 2985-2991

  View details for DOI 10.1039/c3tc32581d

  View details for Web of Science ID 000334123800020

• Nanostructured conductive polypyrrole hydrogels as high-performance, flexible supercapacitor electrodes JOURNAL OF MATERIALS CHEMISTRY A Shi, Y., Pan, L., Liu, B., Wang, Y., Cui, Y., Bao, Z., Yu, G. 2014; 2 (17): 6086-6091

  View details for DOI 10.1039/c4ta00484a

  View details for Web of Science ID 000333580700016

• High-Mobility, Aligned Crystalline Domains of TIPS-Pentacene with Metastable Polymorphs Through Lateral Confinement of Crystal Growth. Advanced materials Giri, G., Park, S., Vosgueritchian, M., Shulaker, M. M., Bao, Z. 2014; 26 (3): 487-493

  Abstract

  Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals. This lateral confinement causes aligned crystal growth, and the smallest patterns of 0.5 μm wide solvent wetting regions promotes formation of highly strained, aligned, and single-crystalline TIPS-pentacene regions with mobility as high as 2.7 cm(2) V(-1) s(-1) .

  View details for DOI 10.1002/adma.201302439

  View details for PubMedID 24133041

• One-dimensional self-confinement promotes polymorph selection in large-area organic semiconductor thin films. Nature communications Giri, G., Li, R., Smilgies, D., Li, E. Q., Diao, Y., Lenn, K. M., Chiu, M., Lin, D. W., Allen, R., Reinspach, J., Mannsfeld, S. C., Thoroddsen, S. T., Clancy, P., Bao, Z., Amassian, A. 2014; 5: 3573-?

  Abstract

  A crystal's structure has significant impact on its resulting biological, physical, optical and electronic properties. In organic electronics, 6,13(bis-triisopropylsilylethynyl)pentacene (TIPS-pentacene), a small-molecule organic semiconductor, adopts metastable polymorphs possessing significantly faster charge transport than the equilibrium crystal when deposited using the solution-shearing method. Here, we use a combination of high-speed polarized optical microscopy, in situ microbeam grazing incidence wide-angle X-ray-scattering and molecular simulations to understand the mechanism behind formation of metastable TIPS-pentacene polymorphs. We observe that thin-film crystallization occurs first at the air-solution interface, and nanoscale vertical spatial confinement of the solution results in formation of metastable polymorphs, a one-dimensional and large-area analogy to crystallization of polymorphs in nanoporous matrices. We demonstrate that metastable polymorphism can be tuned with unprecedented control and produced over large areas by either varying physical confinement conditions or by tuning energetic conditions during crystallization through use of solvent molecules of various sizes.

  View details for DOI 10.1038/ncomms4573

  View details for PubMedID 24736391

• Swelling of Polymer Dielectric Thin Films for Organic-Transistor-Based Aqueous Sensing Applications CHEMISTRY OF MATERIALS Verploegen, E., Sokolov, A. N., Akgun, B., Satija, S. K., Wei, P., Kim, D., Kapelewski, M. T., Bao, Z., Toney, M. F. 2013; 25 (24): 5018-5022

  View details for DOI 10.1021/cm4032013

  View details for Web of Science ID 000329137800022

• Side-Chain Engineering of Isoindigo-Containing Conjugated Polymers Using Polystyrene for High-Performance Bulk Heterojunction Solar Cells CHEMISTRY OF MATERIALS Fang, L., Zhou, Y., Yao, Y., Diao, Y., Lee, W., Appleton, A. L., Allen, R., Reinspach, J., Mannsfeld, S. C., Bao, Z. 2013; 25 (24): 4874-4880

  View details for DOI 10.1021/cm4024259

  View details for Web of Science ID 000329137800006

• Thiol-ene Cross-Linked Polymer Gate Dielectrics for Low-Voltage Organic Thin-Film Transistors CHEMISTRY OF MATERIALS Wang, C., Lee, W., Nakajima, R., Mei, J., Kim, D. H., Bao, Z. 2013; 25 (23): 4806-4812

  View details for DOI 10.1021/cm403203k

  View details for Web of Science ID 000328437300021

• Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries NATURE CHEMISTRY Wang, C., Wu, H., Chen, Z., McDowell, M. T., Cui, Y., Bao, Z. 2013; 5 (12): 1043-1049

  Abstract

  The ability to repair damage spontaneously, which is termed self-healing, is an important survival feature in nature because it increases the lifetime of most living creatures. This feature is highly desirable for rechargeable batteries because the lifetime of high-capacity electrodes, such as silicon anodes, is shortened by mechanical fractures generated during the cycling process. Here, inspired by nature, we apply self-healing chemistry to silicon microparticle (SiMP) anodes to overcome their short cycle-life. We show that anodes made from low-cost SiMPs (~3-8 µm), for which stable deep galvanostatic cycling was previously impossible, can now have an excellent cycle life when coated with a self-healing polymer. We attain a cycle life ten times longer than state-of-art anodes made from SiMPs and still retain a high capacity (up to ~3,000 mA h g(-1)). Cracks and damage in the coating during cycling can be healed spontaneously by the randomly branched hydrogen-bonding polymer used.

  View details for DOI 10.1038/NCHEM.1802

  View details for Web of Science ID 000327450500014

• Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries. Nature chemistry Wang, C., Wu, H., Chen, Z., McDowell, M. T., Cui, Y., Bao, Z. 2013; 5 (12): 1042-8

  Abstract

  The ability to repair damage spontaneously, which is termed self-healing, is an important survival feature in nature because it increases the lifetime of most living creatures. This feature is highly desirable for rechargeable batteries because the lifetime of high-capacity electrodes, such as silicon anodes, is shortened by mechanical fractures generated during the cycling process. Here, inspired by nature, we apply self-healing chemistry to silicon microparticle (SiMP) anodes to overcome their short cycle-life. We show that anodes made from low-cost SiMPs (~3-8 µm), for which stable deep galvanostatic cycling was previously impossible, can now have an excellent cycle life when coated with a self-healing polymer. We attain a cycle life ten times longer than state-of-art anodes made from SiMPs and still retain a high capacity (up to ~3,000 mA h g(-1)). Cracks and damage in the coating during cycling can be healed spontaneously by the randomly branched hydrogen-bonding polymer used.

  View details for DOI 10.1038/nchem.1802

  View details for PubMedID 24256869

• Stretchable and self-healing polymers and devices for electronic skin PROGRESS IN POLYMER SCIENCE Benight, S. J., Wang, C., Tok, J. B., Bao, Z. 2013; 38 (12): 1961-1977

  View details for DOI 10.1016/j.progpolymsci.2013.08.001

  View details for Web of Science ID 000327803700008

• 25th anniversary article: The evolution of electronic skin (e-skin): a brief history, design considerations, and recent progress. Advanced materials Hammock, M. L., Chortos, A., Tee, B. C., Tok, J. B., Bao, Z. 2013; 25 (42): 5997-6038

  Abstract

  Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

  View details for DOI 10.1002/adma.201302240

  View details for PubMedID 24151185

• Conjugated Polymer-Mediated Polymorphism of a High Performance, Small-Molecule Organic Semiconductor with Tuned Intermolecular Interactions, Enhanced Long-Range Order, and Charge Transport CHEMISTRY OF MATERIALS Chen, J., Shao, M., Xiao, K., He, Z., Li, D., Lokitz, B. S., Hensley, D. K., Kilbey, S. M., Anthony, J. E., Keum, J. K., Rondinone, A. J., Lee, W., Hong, S., Bao, Z. 2013; 25 (21): 4378-4386

  View details for DOI 10.1021/cm403039y

  View details for Web of Science ID 000327045000029

• 25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress ADVANCED MATERIALS Hammock, M. L., Chortos, A., Tee, B. C., Tok, J. B., Bao, Z. 2013; 25 (42): 5997-6037

  Abstract

  Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

  View details for DOI 10.1002/adma.201302240

  View details for Web of Science ID 000327801900001

• A rapid and efficient self-healing thermo-reversible elastomer crosslinked with graphene oxide. Advanced materials Wang, C., Liu, N., Allen, R., Tok, J. B., Wu, Y., Zhang, F., Chen, Y., Bao, Z. 2013; 25 (40): 5785-5790

  Abstract

  A self-healing thermo-reversible elastomer is synthesized by cross-linking a hydrogen bonding polymer network with chemically-modified graphene oxide. This nanocomposite allows for both rapid and efficient self-healing (in only several minutes) at room temperature, without the need for any external stimuli (e.g., heating or light exposure), healing agents, plasticizers or solvents.

  View details for DOI 10.1002/adma.201302962

  View details for PubMedID 23946261

• Mechanistic Study on the Solution-Phase n-Doping of 1,3-Dimethyl-2-aryl-2,3-dihydro-1H-benzoimidazole Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Naab, B. D., Guo, S., Olthof, S., Evans, E. G., Wei, P., Millhauser, G. L., Kahn, A., Barlow, S., Marder, S. R., Bao, Z. 2013; 135 (40): 15018-15025

  Abstract

  The discovery of air-stable n-dopants for organic semiconductor materials has been hindered by the necessity of high-energy HOMOs and the air sensitivity of compounds that satisfy this requirement. One strategy for circumventing this problem is to utilize stable precursor molecules that form the active doping complex in situ during the doping process or in a postdeposition thermal- or photo-activation step. Some of us have reported on the use of 1H-benzimidazole (DMBI) and benzimidazolium (DMBI-I) salts as solution- and vacuum-processable n-type dopant precursors, respectively. It was initially suggested that DMBI dopants function as single-electron radical donors wherein the active doping species, the imidazoline radical, is generated in a postdeposition thermal annealing step. Herein we report the results of extensive mechanistic studies on DMBI-doped fullerenes, the results of which suggest a more complicated doping mechanism is operative. Specifically, a reaction between the dopant and host that begins with either hydride or hydrogen atom transfer and which ultimately leads to the formation of host radical anions is responsible for the doping effect. The results of this research will be useful for identifying applications of current organic n-doping technology and will drive the design of next-generation n-type dopants that are air stable and capable of doping low-electron-affinity host materials in organic devices.

  View details for DOI 10.1021/ja403906d

  View details for Web of Science ID 000326356400025

  View details for PubMedID 24011269

• A rapid and efficient self-healing thermo-reversible elastomer crosslinked with graphene oxide. Advanced materials Wang, C., Liu, N., Allen, R., Tok, J. B., Wu, Y., Zhang, F., Chen, Y., Bao, Z. 2013; 25 (40): 5785-5790

  Abstract

  A self-healing thermo-reversible elastomer is synthesized by cross-linking a hydrogen bonding polymer network with chemically-modified graphene oxide. This nanocomposite allows for both rapid and efficient self-healing (in only several minutes) at room temperature, without the need for any external stimuli (e.g., heating or light exposure), healing agents, plasticizers or solvents.

  View details for DOI 10.1002/adma.201302962

  View details for PubMedID 23946261

• STRETCHABLE LEDS Light-emitting electronic skin NATURE PHOTONICS Vosgueritchian, M., Tok, J. B., Bao, Z. 2013; 7 (10): 769-771

  View details for DOI 10.1038/nphoton.2013.251

  View details for Web of Science ID 000325003100005

• Solution-Grown Organic Single-Crystalline p-n Junctions with Ambipolar Charge Transport ADVANCED MATERIALS Fan, C., Zoombelt, A. P., Jiang, H., Fu, W., Wu, J., Yuan, W., Wang, Y., Li, H., Chen, H., Bao, Z. 2013; 25 (40): 5762-?

  Abstract

  Organic single-crystalline p-n junctions are grown from mixed solutions. First, C60 crystals (n-type) form and, subsequently, C8-BTBT crystals (p-type) nucleate heterogeneously on the C60 crystals. Both crystals continue to grow simultaneously into single-crystalline p-n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single-crystalline p-n junctions.

  View details for DOI 10.1002/adma.201302605

  View details for Web of Science ID 000330773400011

  View details for PubMedID 23956037

• High Mobility N-Type Transistors Based on Solution-Sheared Doped 6,13-Bis(triisopropylsilylethynyl)pentacene Thin Films. Advanced materials Naab, B. D., Himmelberger, S., Diao, Y., Vandewal, K., Wei, P., Lussem, B., Salleo, A., Bao, Z. 2013; 25 (33): 4663-4667

  Abstract

  An N-Type organic thin-film transistor (OTFT) based on doped 6,13-Bis(triisopropylsilylethynyl)pentacene is presented. A transition from p-type to n-type occurrs with increasing doping concentrations, and the highest performing n-channel OTFTs are obtained with 50 mol% dopant. X-ray diffraction, scanning Auger microscopy, and secondary ionization mass spectrometry are used to characterize the morphology of the blends. The high performance of the obtained transistors is attributed to the highly crystalline and aligned nature of the doped thin films.

  View details for DOI 10.1002/adma.201205098

  View details for PubMedID 23813467

• Direct growth of aligned graphitic nanoribbons from a DNA template by chemical vapour deposition. Nature communications Sokolov, A. N., Yap, F. L., Liu, N., Kim, K., Ci, L., Johnson, O. B., Wang, H., Vosgueritchian, M., Koh, A. L., Chen, J., Park, J., Bao, Z. 2013; 4: 2402-?

  Abstract

  Graphene, laterally confined within narrow ribbons, exhibits a bandgap and is envisioned as a next-generation material for high-performance electronics. To take advantage of this phenomenon, there is a critical need to develop methodologies that result in graphene ribbons <10 nm in width. Here we report the use of metal salts infused within stretched DNA as catalysts to grow nanoscopic graphitic nanoribbons. The nanoribbons are termed graphitic as they have been determined to consist of regions of sp(2) and sp(3) character. The nanoscopic graphitic nanoribbons are micrometres in length, <10 nm in width, and take on the shape of the DNA template. The DNA strand is converted to a graphitic nanoribbon by utilizing chemical vapour deposition conditions. Depending on the growth conditions, metallic or semiconducting graphitic nanoribbons are formed. Improvements in the growth method have potential to lead to bottom-up synthesis of pristine single-layer graphene nanoribbons.

  View details for DOI 10.1038/ncomms3402

  View details for PubMedID 23989553

• Aligned SWNT Films from Low-Yield Stress Gels and Their Transparent Electrode Performance ACS APPLIED MATERIALS & INTERFACES Allen, R., Fuller, G. G., Bao, Z. 2013; 5 (15): 7244-7252

  Abstract

  Carbon nanotube films are promising for transparent electrodes for solar cells and displays. Large-area alignment of the nanotubes in these films is needed to minimize the sheet resistance. We present a novel coating method to coat high-density, aligned nanotubes over large areas. Carbon nanotube gel dispersions used in this study have aligned domains and a low yield stress. A simple shearing force allows these domains to uniformly align. We use this to correlate the transparent electrode performance of single-walled carbon nanotube films with the level of partial alignment. We have found that the transparent electrode performance improves with increasing levels of alignment and in a manner slightly better than what has been previously predicted.

  View details for DOI 10.1021/am401592v

  View details for Web of Science ID 000323241100066

  View details for PubMedID 23823600

• Effects of Odd-Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Akkerman, H. B., Mannsfeld, S. C., Kaushik, A. P., Verploegen, E., Burnier, L., Zoombelt, A. P., Saathoff, J. D., Hong, S., Atahan-Evrenk, S., Liu, X., Aspuru-Guzik, A., Toney, M. F., Clancy, P., Bao, Z. 2013; 135 (30): 11006-11014

  Abstract

  Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5'bis(4-alkylphenyl)-2,2'-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling.

  View details for DOI 10.1021/ja400015e

  View details for Web of Science ID 000322752900031

  View details for PubMedID 23822850

• Observation of orientation-dependent photovoltaic behaviors in aligned organic nanowires APPLIED PHYSICS LETTERS Oh, J. H., Wong, L. H., Yu, H., Park, Y. J., Kim, J. M., Bao, Z. 2013; 103 (5)

  View details for DOI 10.1063/1.4817299

  View details for Web of Science ID 000322723000099

• Ultra-Smooth and Ultra-Strong Ion-Exchanged Glass as Substrates for Organic Electronics ADVANCED FUNCTIONAL MATERIALS Kaefer, D., He, M., Li, J., Pambianchi, M. S., Feng, J., Mauro, J. C., Bao, Z. 2013; 23 (25): 3233-3238

  View details for DOI 10.1002/adfm.201202009

  View details for Web of Science ID 000322362500012

• Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nature materials Diao, Y., Tee, B. C., Giri, G., Xu, J., Kim, D. H., Becerril, H. A., Stoltenberg, R. M., Lee, T. H., Xue, G., Mannsfeld, S. C., Bao, Z. 2013; 12 (7): 665-671

  Abstract

  Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach-termed fluid-enhanced crystal engineering (FLUENCE)-that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm(2) V(-1) s(-1) and 11 cm(2) V(-1) s(-1). FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics.

  View details for DOI 10.1038/nmat3650

  View details for PubMedID 23727951

• Atomic layer deposition of high-k dielectrics on single-walled carbon nanotubes: a Raman study NANOTECHNOLOGY Liyanage, L. S., Cott, D. J., Delabie, A., Van Elshocht, S., Bao, Z., Wong, H. P. 2013; 24 (24)

  Abstract

  Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, to realize a carbon nanotube field effect transistor (CNTFET) with excellent gate control, the high-k dielectrics between the CNT and the metal gate must have superb electrical properties and extremely high uniformity. Thus it is essential to understand the interactions between high-k materials and the SWCNTs to effectively control the transistor characteristics. In this study, we investigate the effects of atomic layer deposited (ALD) high-k dielectrics (Al2O3 and HfO2) on SWCNTs using Raman spectroscopy. We subjected the SWCNTs to various ALD cycles and studied the nucleation and growth of ALD dielectrics at defect sites using scanning electron microscopy and transmission electron microscopy images. We analyzed these samples using Raman spectroscopy and x-ray photoelectron spectroscopy. The Raman peak shifts of the G-peak and the 2D (G') peaks suggest doping and stress induced effects on the CNTs by the surrounding high-k oxide environment. Trends in the G-peak FWHM and G/D-peak ratios were identified and compared between Al2O3 and HfO2. We confirmed the ALD-deposited HfO2 is polycrystalline using x-ray diffraction and analyzed dielectric-CNT bonding states using XPS measurements. This study provides insights on the effects of ALD high-k materials on SWCNTs for future high-speed transistor applications.

  View details for DOI 10.1088/0957-4484/24/24/245703

  View details for Web of Science ID 000319384300021

  View details for PubMedID 23696347

• Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. Nature communications Wu, H., Yu, G., Pan, L., Liu, N., McDowell, M. T., Bao, Z., Cui, Y. 2013; 4: 1943-?

  View details for DOI 10.1038/ncomms2941

  View details for PubMedID 23733138

• Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors. ACS nano Hammock, M. L., Knopfmacher, O., Naab, B. D., Tok, J. B., Bao, Z. 2013; 7 (5): 3970-3980

  Abstract

  Biodetection using organic field-effect transistors (OFETs) is gaining increasing interest for applications as diverse as food security, environmental monitoring, and medical diagnostics. However, there still lacks a comprehensive, empirical study on the fundamental limits of OFET sensors. In this paper, we present a thorough study of the various parameters affecting biosensing using an OFET decorated with gold nanoparticle (AuNP) binding sites. These parameters include the spacing between receptors, pH of the buffer, and ionic strength of the buffer. To this end, we employed the thrombin protein and its corresponding DNA binding aptamer to form our model detection system. We demonstrate a detection limit of 100 pM for this protein with high selectivity over other proteases in situ. We describe herein a feasible approach for protein detection with OFETs and a thorough investigation of parameters governing biodetection events using OFETs. Our obtained results should provide important guidelines to tailor the sensor's dynamic range to suit other desired OFET-based biodetection applications.

  View details for DOI 10.1021/nn305903q

  View details for PubMedID 23597051

• Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mei, J., Diao, Y., Appleton, A. L., Fang, L., Bao, Z. 2013; 135 (18): 6724-6746

  Abstract

  The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm(2)/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.

  View details for DOI 10.1021/ja400881n

  View details for Web of Science ID 000318839300001

  View details for PubMedID 23557391

• Tuning the Dirac Point in CVD-Grown Graphene through Solution Processed n-Type Doping with 2-(2-Methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole. Nano letters Wei, P., Liu, N., Lee, H. R., Adijanto, E., Ci, L., Naab, B. D., Zhong, J. Q., Park, J., Chen, W., Cui, Y., Bao, Z. 2013; 13 (5): 1890-1897

  Abstract

  Controlling the Dirac point of graphene is essential for complementary circuits. Here, we describe the use of 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole (o-MeO-DMBI) as a strong n-type dopant for chemical-vapor-deposition (CVD) grown graphene. The Dirac point of graphene can be tuned significantly by spin-coating o-MeO-DMBI solutions on the graphene sheets at different concentrations. The transport of graphene can be changed from p-type to ambipolar and finally n-type. The electron transfer between o-MeO-DMBI and graphene was additionally confirmed by Raman imaging and photoemission spectroscopy (PES) measurements. Finally, we fabricated a complementary inverter via inkjet printing patterning of o-MeO-DMBI solutions on graphene to demonstrate the potential of o-MeO-DMBI n-type doping on graphene for future applications in electrical devices.

  View details for DOI 10.1021/nl303410g

  View details for PubMedID 23537351

• p-Channel Field-Effect Transistors Based on C-60 Doped with Molybdenum Trioxide ACS APPLIED MATERIALS & INTERFACES Lee, T. H., Luessem, B., Kim, K., Giri, G., Nishi, Y., Bao, Z. 2013; 5 (7): 2337-2341

  Abstract

  Fullerene (C60) is a well-known n-channel organic semiconductor. We demonstrate that p-channel C60 field-effect transistors are possible by doping with molybdenum trioxide (MoO3). The device performance of the p-channel C60 field-effect transistors, such as mobility, threshold voltage, and on/off ratio is varied in a controlled manner by changing doping concentration. This work demonstrates the utility of charge transfer doping to obtain both n- and p-channel field-effect transistors with a single organic semiconductor.

  View details for DOI 10.1021/am3026568

  View details for Web of Science ID 000317549100007

  View details for PubMedID 23446111

• Scalable Synthesis of Fused Thiophene-Diketopyrrolopyrrole Semiconducting Polymers Processed from Nonchlorinated Solvents into High Performance Thin Film Transistors CHEMISTRY OF MATERIALS Matthews, J. R., Niu, W., Tandia, A., Wallace, A. L., Hu, J., Lee, W., Giri, G., Mannsfeld, S. C., Xie, Y., Cai, S., Fong, H. H., Bao, Z., He, M. 2013; 25 (5): 782-789

  View details for DOI 10.1021/cm303953e

  View details for Web of Science ID 000316168800017

• Scalable and Selective Dispersion of Semiconducting Arc-Discharged Carbon Nanotubes by Dithiafulvalene/Thiophene Copolymers for Thin Film Transistors ACS NANO Wang, H., Mei, J., Liu, P., Schmidt, K., Jimenez-Oses, G., Osuna, S., Fang, L., Tassone, C. J., Zoombelt, A. P., Sokolov, A. N., Houk, K. N., Toney, M. F., Bao, Z. 2013; 7 (3): 2659-2668

  Abstract

  We report a simple and scalable method to enrich large quantities of semiconducting arc-discharged single-walled carbon nanotubes (SWNTs) with diameters of 1.1-1.8 nm using dithiafulvalene/thiophene copolymers. Stable solutions of highly individualized and highly enriched semiconducting SWNTs were obtained after a simple sonication and centrifuge process. Molecular dynamics (MD) simulations of polymer backbone interactions with and without side chains indicated that the presence of long alkyl side chains gave rise to the selectivity toward semiconducting tubes, indicating the importance of the roles of the side chains to both solubilize and confer selectivity to the polymers. We found that, by increasing the ratio of thiophene to dithiafulvalene units in the polymer backbone (from pDTFF-1T to pDTFF-3T), we can slightly improve the selectivity toward semiconducting SWNTs. This is likely due to the more flexible backbone of pDTFF-3T that allows the favorable wrapping of SWNTs with certain chirality as characterized by small-angle X-ray scattering. However, the dispersion yield was reduced from pDTFF-1T to pDTFF-3T. MD simulations showed that the reduction is due to the smaller polymer/SWNT contact area, which reduces the dispersion ability of pDTFF-3T. These experimental and modeling results provide a better understanding for future rational design of polymers for sorting SWNTs. Finally, high on/off ratio solution-processed thin film transistors were fabricated from the sorted SWNTs to confirm the selective dispersion of semiconducting arc-discharge SWNTs.

  View details for DOI 10.1021/nn4000435

  View details for PubMedID 23402644

• Hybrid nanostructured materials for high-performance electrochemical capacitors NANO ENERGY Yu, G., Xie, X., Pan, L., Bao, Z., Cui, Y. 2013; 2 (2): 213-234

  View details for DOI 10.1016/j.nanoen.2012.10.006

  View details for Web of Science ID 000318319700009

• Look fast: Crystallization of conjugated molecules during solution shearing probed in-situ and in real time by X-ray scattering PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Smilgies, D., Li, R., Giri, G., Chou, K. W., Diao, Y., Bao, Z., Amassian, A. 2013; 7 (3): 177-179

  View details for DOI 10.1002/pssr.201206507

  View details for Web of Science ID 000318069900002

• A Comparison of the Properties of Two Structurally Equivalent but Regiochemically Different Mono-Alkylated Polybithiophenes Prepared Through AABB-Type Stille Polycondensation JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Lundin, P. M., Giri, G., Bao, Z. 2013; 51 (4): 908-915

  View details for DOI 10.1002/pola.26448

  View details for Web of Science ID 000314150500018

• Flexible Wireless Temperature Sensors Based on Ni Microparticle-Filled Binary Polymer Composites ADVANCED MATERIALS Jeon, J., Lee, H., Bao, Z. 2013; 25 (6): 850-855

  View details for DOI 10.1002/adma.201204082

  View details for Web of Science ID 000314653300006

  View details for PubMedID 23233317

• Comparison of the Photovoltaic Characteristics and Nanostructure of Fullerenes Blended with Conjugated Polymers with Siloxane-Terminated and Branched Aliphatic Side Chains CHEMISTRY OF MATERIALS Kim, D. H., Ayzner, A. L., Appleton, A. L., Schmidt, K., Mei, J., Toney, M. F., Bao, Z. 2013; 25 (3): 431-440

  View details for DOI 10.1021/cm303572d

  View details for Web of Science ID 000315018500020

• High-Performance Phototransistors Based on Single-Crystalline n-Channel Organic Nanowires and Photogenerated Charge-Carrier Behaviors ADVANCED FUNCTIONAL MATERIALS Yu, H., Bao, Z., Oh, J. H. 2013; 23 (5): 629-639

  View details for DOI 10.1002/adfm.201201848

  View details for Web of Science ID 000314468600012

• Oriented, polymer-stabilized carbon nanotube films: influence of dispersion rheology NANOTECHNOLOGY Allen, R., Bao, Z., Fuller, G. G. 2013; 24 (1)

  Abstract

  Thin carbon nanotube films have great potential for transparent electrodes for solar cells and displays. One advantage for using carbon nanotubes is the potential for solution processing. However, research has not been done to connect solution rheological properties with the corresponding film characteristics. Here we study the rheological properties of single-walled carbon nanotube/polythiophene composite dispersions to better understand the alignment that can be achieved during deposition. Several parameters are varied to explore the cause of the alignment and the requirements of achieving a uniform, aligned carbon nanotube/polythiophene film. By understanding the dispersions thoroughly, the film quality can be predicted.

  View details for DOI 10.1088/0957-4484/24/1/015709

  View details for Web of Science ID 000312272500031

  View details for PubMedID 23221393

• A review of fabrication and applications of carbon nanotube film-based flexible electronics NANOSCALE Park, S., Vosguerichian, M., Bao, Z. 2013; 5 (5): 1727-1752

  Abstract

  Flexible electronics offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags. Carbon nanotubes (CNTs) are a promising material for flexible electronics, both as the channel material in field-effect transistors (FETs) and as transparent electrodes, due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. In this feature article, we review the recent progress of CNTs in flexible electronics by describing both the processing and the applications of CNT-based flexible devices. To employ CNTs as the channel material in FETs, single-walled carbon nanotubes (SWNTs) are used. There are generally two methods of depositing SWNTs on flexible substrates-transferring CVD-grown SWNTs or solution-depositing SWNTs. Since CVD-grown SWNTs can be highly aligned, they often outperform solution-processed SWNT films that are typically in the form of random network. However, solution-based SWNTs can be printed at a large-scale and at low-cost, rendering them more appropriate for manufacturing. In either case, the removal of metallic SWNTs in an effective and a scalable manner is critical, which must still be developed and optimized. Nevertheless, promising results demonstrating SWNT-based flexible circuits, displays, RF-devices, and biochemical sensors have been reported by various research groups, proving insight into the exciting possibilities of SWNT-based FETs. In using carbon nanotubes as transparent electrodes (TEs), two main strategies have been implemented to fabricate highly conductive, transparent, and mechanically compliant films-superaligned films of CNTs drawn from vertically grown CNT forests using the "dry-drawing" technique and the deposition or embedding of CNTs onto flexible or stretchable substrates. The main challenge for CNT based TEs is to fabricate films that are both highly conductive and transparent. These CNT based TEs have been used in stretchable and flexible pressure, strain, and chemical and biological sensors. In addition, they have also been used as the anode and cathode in flexible light emitting diodes, solar cells, and supercapacitors. In summary, there are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.

  View details for DOI 10.1039/c3nr33560g

  View details for Web of Science ID 000314931900002

  View details for PubMedID 23381727

• Direct growth of aligned graphitic nanoribbons from a DNA template by chemical vapour deposition. Nature communications Sokolov, A. N., Yap, F. L., Liu, N., Kim, K., Ci, L., Johnson, O. B., Wang, H., Vosgueritchian, M., Koh, A. L., Chen, J., Park, J., Bao, Z. 2013; 4: 2402-?

  Abstract

  Graphene, laterally confined within narrow ribbons, exhibits a bandgap and is envisioned as a next-generation material for high-performance electronics. To take advantage of this phenomenon, there is a critical need to develop methodologies that result in graphene ribbons <10 nm in width. Here we report the use of metal salts infused within stretched DNA as catalysts to grow nanoscopic graphitic nanoribbons. The nanoribbons are termed graphitic as they have been determined to consist of regions of sp(2) and sp(3) character. The nanoscopic graphitic nanoribbons are micrometres in length, <10 nm in width, and take on the shape of the DNA template. The DNA strand is converted to a graphitic nanoribbon by utilizing chemical vapour deposition conditions. Depending on the growth conditions, metallic or semiconducting graphitic nanoribbons are formed. Improvements in the growth method have potential to lead to bottom-up synthesis of pristine single-layer graphene nanoribbons.

  View details for DOI 10.1038/ncomms3402

  View details for PubMedID 23989553

• Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. Nature communications Wu, H., Yu, G., Pan, L., Liu, N., McDowell, M. T., Bao, Z., Cui, Y. 2013; 4: 1943-?

  Abstract

  Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).

  View details for DOI 10.1038/ncomms2941

  View details for PubMedID 23733138

• Cooperative Spectrum Sensing With Adaptive Energy Threshold Control and Efficient Data Fusion 2nd IEEE/CIC International Conference on Communications in China (ICCC) Ling, X., Bao, Z., Wen, H., Wu, B., Xu, S., Pan, L. IEEE. 2013: 362–367

  View details for Web of Science ID 000334936200065

• A Novel X-band Differential Bandpass Filter Based on Oversized Substrate Integrated Waveguide Cavity Cross Strait Quad-Regional Radio Science and Wireless Technology Conference (CSQRWC) Jin, C., Chen, J., Chu, H., Bao, Z. IEEE. 2013: 62–65

  View details for Web of Science ID 000331839200018

• Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring. Nature communications Schwartz, G., Tee, B. C., Mei, J., Appleton, A. L., Kim, D. H., Wang, H., Bao, Z. 2013; 4: 1859-?

  Abstract

  Flexible pressure sensors are essential parts of an electronic skin to allow future biomedical prostheses and robots to naturally interact with humans and the environment. Mobile biomonitoring in long-term medical diagnostics is another attractive application for these sensors. Here we report the fabrication of flexible pressure-sensitive organic thin film transistors with a maximum sensitivity of 8.4 kPa(-1), a fast response time of <10 ms, high stability over >15,000 cycles and a low power consumption of <1 mW. The combination of a microstructured polydimethylsiloxane dielectric and the high-mobility semiconducting polyisoindigobithiophene-siloxane in a monolithic transistor design enabled us to operate the devices in the subthreshold regime, where the capacitance change upon compression of the dielectric is strongly amplified. We demonstrate that our sensors can be used for non-invasive, high fidelity, continuous radial artery pulse wave monitoring, which may lead to the use of flexible pressure sensors in mobile health monitoring and remote diagnostics in cardiovascular medicine.

  View details for DOI 10.1038/ncomms2832

  View details for PubMedID 23673644

• Tuning the Dirac Point in CVD-Grown Graphene through Solution Processed n-Type Doping with 2-(2-Methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzoimidazole Nano Lett. Wei, P., Liu, N., Lee, H., R., Adijanto, E., Ci, L., Naab, B., D., Bao, Z. 2013; 13: 1890-1897
• Stretchable LEDs: Light-emitting electronic skin Nature Photonics Vosgueritchian, M., Tok, J., B.-H., Bao, Z. 2013; 7: 769-771
• Ultra-High Mobility Transparent Organic Thin Film Transistors Via an Off-Center Spin-Coating Method Nature Comm. Yuan, Y., Giri, G., Ayzner, A., L., Zoombelt, A., P., Mannsfeld, S., C.B., Chen, J., Bao, Z. 2013
• Stable Li-ion Battery Anodes by In-situ Polymerization of Conducting Hydrogel to Conformally Coat Silicon Nanoparticles Nature Comm. Wu, H., Yu, G., Pan, L., Liu, N., McDowell, M., T., Bao, Z. 2013; 4: 1943

  Abstract

  Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).

  View details for DOI 10.1038/ncomms2941

• Solution-Grown Organic Single-Crystalline p-n Junctions with Ambipolar Charge Transport Adv. Mater. Fan, C., Zoombelt, A., P., Jiang, H., Fu, W., Wu, J., Yuan, W., Bao, Z. 2013
• Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains Nature Materials Diao, Y., Tee, B., C-K., Giri, G., Xu, J., Kim, D., H., Becerril, H., A., Bao, Z. 2013; 12: 665-671

  Abstract

  Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach-termed fluid-enhanced crystal engineering (FLUENCE)-that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm(2) V(-1) s(-1) and 11 cm(2) V(-1) s(-1). FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics.

  View details for DOI 10.1038/nmat3650

• Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring Nature Comm. Schwartz, G., Tee, B., C-K., Mei, J., Appleton, A., L., Kim, H., D, Wang, H., Bao, Z. 2013; 4: 1859

  Abstract

  Flexible pressure sensors are essential parts of an electronic skin to allow future biomedical prostheses and robots to naturally interact with humans and the environment. Mobile biomonitoring in long-term medical diagnostics is another attractive application for these sensors. Here we report the fabrication of flexible pressure-sensitive organic thin film transistors with a maximum sensitivity of 8.4 kPa(-1), a fast response time of <10 ms, high stability over >15,000 cycles and a low power consumption of <1 mW. The combination of a microstructured polydimethylsiloxane dielectric and the high-mobility semiconducting polyisoindigobithiophene-siloxane in a monolithic transistor design enabled us to operate the devices in the subthreshold regime, where the capacitance change upon compression of the dielectric is strongly amplified. We demonstrate that our sensors can be used for non-invasive, high fidelity, continuous radial artery pulse wave monitoring, which may lead to the use of flexible pressure sensors in mobile health monitoring and remote diagnostics in cardiovascular medicine.

  View details for DOI 10.1038/ncomms2832

• Effects of Odd-Even Side Chain Length of Alkyl-Substituted Diphenyl-bithiophenes on First Monolayer Thin Film Packing Structure J. Am. Chem. Soc. Akkerman, H., B., Mannsfeld, S., C.B., Kaushik, A., P., Verploegen, E., Burnier, L., Zoombelt, A., P., Bao, Z. 2013; 135: 11006-11014
• An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film Nature Comm. Pan, L., Chortos, A., Yu, G., Wang, Y., Isaacson, S., Allen, R., Bao, Z. 2013
• A Rapid and Efficient Self-Healing Thermo-Reversible Elastomer Crosslinked with Graphene Oxide Adv. Mater. Wang, C., Liu, N., Allen, R., Tok, J., B.-H., Wu, Y., Zhang, F., Bao, Z. 2013; 25: 5785-5790
• A Flexible Bimodal Sensor Array for Simultaneous Sensing of Pressure and Temperature Adv. Mater. Tien, N., T., Jeon, S., Kim, D., I., Trung, T., Q., Jang, M., Hwang, B., U., Bao, Z. 2013
• Confined organization of fullerene units along high polymer chains JOURNAL OF MATERIALS CHEMISTRY C Fang, L., Liu, P., Sveinbjornsson, B. R., Atahan-Evrenk, S., Vandewal, K., Osuna, S., Jimenez-Oses, G., Shrestha, S., Giri, G., Wei, P., Salleo, A., Aspuru-Guzik, A., Grubbs, R. H., Houk, K. N., Bao, Z. 2013; 1 (36): 5747-5755

  View details for DOI 10.1039/c3tc31158a

  View details for Web of Science ID 000323578000020

• Observation of orientation-dependent photovoltaic behaviors in aligned organic nanowires Appl. Phys. Lett. Oh, J., H., Wong, L., H., Yu, H., Park, Y., J., Kim, J., M., Bao, Z. 2013; 103: 53304
• Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors ACS Nano Hammock, M., L., Knopfmacher, O., Naab, B., D., Tok, J., B., Bao, Z. 2013; 7: 3970-3980
• High Mobility N-Type Transistors Based on Solution-sheared Doped TIPS-pentacene Thin Films Adv. Mat. Naab, B., D., Himmelberger, S., Diao, Y., Vandewal, k., Wei, P., Lussem, B., Bao, Z. 2013; 25: 4663-4667
• Direct Growth of Aligned Graphitic Nanoribbons from a DNA Template by Chemical Vapour Deposition Nature Comm. Sokolov, A., N., Yap, F., L., Liu, L., Kim, K., Ci, L., Johnson, O., B., Bao, Z. 2013; 4: 2402
• 25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress Adv. Mat. Hammock, M., L., Chortos, A., Tee, B., C-K., Tok, J., B.-H., Bao, Z. 2013; 25: 5997-6038
• Highly stable organic polymer field-effect transistor sensor for selective detection in the marine environment Nature Comm. Knopfmacher, O., Hammock, M., L., Appleton, A., L., Schwartz, G., Mei, J., Lei, T., Bao, Z. 2013
• Mechanistic Study on the Solution-Phase n-Doping of 1,3-Dimethyl-2-aryl-2,3-dihydro-1H-benzoimidazole Derivatives J. Am. Chem. Soc. Naab, B., D., Guo, S., Olthof, S., Evans, E. G., B., Wei, P., Millhauser, G., L., Bao, Z. 2013
• Toward high-mobility organic field-effect transistors: Control of molecular packing and large-area fabrication of single-crystal-based devices MRS BULLETIN Li, H., Giri, G., Tok, J. B., Bao, Z. 2013; 38 (1): 34-42

  View details for DOI 10.1557/mrs.2012.309

  View details for Web of Science ID 000317549400011

• An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications NATURE NANOTECHNOLOGY Tee, B. C., Wang, C., Allen, R., Bao, Z. 2012; 7 (12): 825-832

  Abstract

  Pressure sensitivity and mechanical self-healing are two vital functions of the human skin. A flexible and electrically conducting material that can sense mechanical forces and yet be able to self-heal repeatably can be of use in emerging fields such as soft robotics and biomimetic prostheses, but combining all these properties together remains a challenging task. Here, we describe a composite material composed of a supramolecular organic polymer with embedded nickel nanostructured microparticles, which shows mechanical and electrical self-healing properties at ambient conditions. We also show that our material is pressure- and flexion-sensitive, and therefore suitable for electronic skin applications. The electrical conductivity can be tuned by varying the amount of nickel particles and can reach values as high as 40 S cm(-1). On rupture, the initial conductivity is repeatably restored with ∼90% efficiency after 15 s healing time, and the mechanical properties are completely restored after ∼10 min. The composite resistance varies inversely with applied flexion and tactile forces. These results demonstrate that natural skin's repeatable self-healing capability can be mimicked in conductive and piezoresistive materials, thus potentially expanding the scope of applications of current electronic skin systems.

  View details for DOI 10.1038/NNANO.2012.192

  View details for Web of Science ID 000312003700019

  View details for PubMedID 23142944

• Toward mechanically robust and intrinsically stretchable organic solar cells: Evolution of photovoltaic properties with tensile strain SOLAR ENERGY MATERIALS AND SOLAR CELLS Lipomi, D. J., Chong, H., Vosgueritchian, M., Mei, J., Bao, Z. 2012; 107: 355-365

  View details for DOI 10.1016/j.solmat.2012.07.013

  View details for Web of Science ID 000311270000048

• A comparison of two air-stable molecular n-dopants for C-60 ORGANIC ELECTRONICS Menke, T., Wei, P., Ray, D., Kleemann, H., Naab, B. D., Bao, Z., Leo, K., Riede, M. 2012; 13 (12): 3319-3325

  View details for DOI 10.1016/j.orgel.2012.09.024

  View details for Web of Science ID 000311681600076

• A simple droplet pinning method for polymer film deposition for measuring charge transport in a thin film transistor ORGANIC ELECTRONICS Li, H., Mei, J., Ayzner, A. L., Toney, M. F., Tok, J. B., Bao, Z. 2012; 13 (11): 2450-2460

  View details for DOI 10.1016/j.orgel.2012.07.011

  View details for Web of Science ID 000311177700035

• Evaluation of Solution-Processable Carbon-Based Electrodes for All-Carbon Solar Cells ACS NANO Ramuz, M. P., Vosgueritchian, M., Wei, P., Wang, C., Gao, Y., Wu, Y., Chen, Y., Bao, Z. 2012; 6 (11): 10384-10395

  Abstract

  Carbon allotropes possess unique and interesting physical, chemical, and electronic properties that make them attractive for next-generation electronic devices and solar cells. In this report, we describe our efforts into the fabrication of the first reported all-carbon solar cell in which all components (the anode, active layer, and cathode) are carbon based. First, we evaluate the active layer, on standard electrodes, which is composed of a bilayer of polymer sorted semiconducting single-walled carbon nanotubes and C(60). This carbon-based active layer with a standard indium tin oxide anode and metallic cathode has a maximum power conversion efficiency of 0.46% under AM1.5 Sun illumination. Next, we describe our efforts in replacing the electrodes with carbon-based electrodes, to demonstrate the first all-carbon solar cell, and discuss the remaining challenges associated with this process.

  View details for DOI 10.1021/nn304410w

  View details for Web of Science ID 000311521700114

  View details for PubMedID 23113673

• Manipulating the Morphology of P3HT-PCBM Bulk Heterojunction Blends with Solvent Vapor Annealing CHEMISTRY OF MATERIALS Verploegen, E., Miller, C. E., Schmidt, K., Bao, Z., Toney, M. F. 2012; 24 (20): 3923-3931

  View details for DOI 10.1021/cm302312a

  View details for Web of Science ID 000310095100012

• TIPS-pentacene crystalline thin film growth ORGANIC ELECTRONICS Akkerman, H. B., Li, H., Bao, Z. 2012; 13 (10): 2056-2062

  View details for DOI 10.1016/j.orgel.2012.06.019

  View details for Web of Science ID 000309591200039

• Dispersion of single walled carbon nanotubes in amidine solvents NANOTECHNOLOGY Barman, S. N., Pan, D., Vosgueritchian, M., Zoombelt, A. P., Galli, G., Bao, Z. 2012; 23 (34)

  Abstract

  The excellent electronic and material properties of single walled carbon nanotubes (SWNTs) makes this nanomaterial very attractive for incorporation into flexible and stretchable electronics. However, the widespread application of SWNTs in electronic devices is still limited. To purify, process and place SWNTs, appropriate solvents for dispersion are needed. However, a fundamental understanding of the reasons why certain solvents are capable of dispersing SWNTs is still missing. Here we report on two new potential solvents containing amidine moieties, 1,8-diazabicycloundec-7-ene (DBU) and 1,5-diazabicyclo(4.3.0)non-5-ene (DBN). Even though these solvents' molecular structures differ by only two -CH(2)- groups, we found that DBU is capable of dispersing SWNTs, while DBN is not. We carried out density functional theory (DFT) calculations to investigate the interaction between DBU and DBN, and we elucidated the reasons for the different performances of the two solvents. DBU has a preferential edge-on interaction with the SWNT, thus allowing for a higher solvent coverage than DBN. In addition, the CH(2)-SWNT interaction present for DBU substantially increases the adsorption energy compared to DBN. Our results point to the important interplay between the interaction of pi electrons, nitrogen lone pairs and the -CH(2)- groups present in aprotic solvent molecules and the delocalized pi electrons in SWNTs.

  View details for DOI 10.1088/0957-4484/23/34/344011

  View details for Web of Science ID 000307812000012

  View details for PubMedID 22885377

• Work function recovery of air exposed molybdenum oxide thin films APPLIED PHYSICS LETTERS Irfan, I., Turinske, A. J., Bao, Z., Gao, Y. 2012; 101 (9)

  View details for DOI 10.1063/1.4748978

  View details for Web of Science ID 000308408100070

• Engineering the metal gate electrode for controlling the threshold voltage of organic transistors APPLIED PHYSICS LETTERS Chung, Y., Johnson, O., Deal, M., Nishi, Y., Murmann, B., Bao, Z. 2012; 101 (6)

  View details for DOI 10.1063/1.4739511

  View details for Web of Science ID 000307862400089

• Strong and Stable Doping of Carbon Nanotubes and Graphene by MoOx for Transparent Electrodes NANO LETTERS Hellstrom, S. L., Vosgueritchian, M., Stoltenberg, R. M., Irfan, I., Hammock, M., Wang, Y. B., Jia, C., Guo, X., Gao, Y., Bao, Z. 2012; 12 (7): 3574-3580

  Abstract

  MoO(x) has been used for organic semiconductor doping, but it had been considered an inefficient and/or unstable dopant. We report that MoO(x) can strongly and stably dope carbon nanotubes and graphene. Thermally annealed MoO(x)-CNT composites can form durable thin film electrodes with sheet resistances of 100 Ω/sq at 85% transmittance plain and 85 Ω/sq at 83% transmittance with a PEDOT:PSS adlayer. Sheet resistances change less than 10% over 20 days in ambient and less than 2% with overnight heating to 300 °C in air. The MoO(x) can be easily deposited either by thermal evaporation or from solution-based precursors. Excellent stability coupled with high conductivity makes MoO(x)-CNT composites extremely attractive candidates for practical transparent electrodes.

  View details for DOI 10.1021/nl301207e

  View details for Web of Science ID 000306296200037

  View details for PubMedID 22694046

• Transparent, Optical, Pressure-Sensitive Artificial Skin for Large-Area Stretchable Electronics ADVANCED MATERIALS Ramuz, M., Tee, B. C., Tok, J. B., Bao, Z. 2012; 24 (24): 3223-3227

  Abstract

  Optical pressure sensors are highly responsive and are unaffected by surrounding parameters such as electronic noise, humidity, temperature, etc. A new type of optical pressure sensor is described that demonstrates the stretchability and transparency of a polydimethylsiloxane waveguide, while also serving as a substrate. The pressure sensors are both robust and easy to fabricate over a large area.

  View details for DOI 10.1002/adma.201200523

  View details for Web of Science ID 000305450500009

  View details for PubMedID 22641411

• Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Pan, L., Yu, G., Zhai, D., Lee, H. R., Zhao, W., Liu, N., Wang, H., Tee, B. C., Shi, Y., Cui, Y., Bao, Z. 2012; 109 (24): 9287-9292

  Abstract

  Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (~480 F·g(-1)), unprecedented rate capability, and cycling stability (~83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (~0.3 s) and superior sensitivity (~16.7 μA · mM(-1)). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.

  View details for DOI 10.1073/pnas.1202636109

  View details for Web of Science ID 000305511300024

  View details for PubMedID 22645374

  View details for PubMedCentralID PMC3386113

• Using Nitrile Functional Groups to Replace Amines for Solution-Deposited Single-Walled Carbon Nanotube Network Films ACS NANO Opatkiewicz, J. P., LeMieux, M. C., Liu, D., Vosgueritchian, M., Barman, S. N., Elkins, C. M., Hedrick, J., Bao, Z. 2012; 6 (6): 4845-4853

  Abstract

  Amine-terminated self-assembled monolayers (SAMs) can be utilized to selectively adsorb semiconducting single-walled carbon nanotubes (S-SWNTs), but are not ideal. Formation of these monolayer films from silanes can be dramatically influenced by atmospheric and other processing conditions, resulting in poor-quality SAMs or irreproducible results. The surface sorting method of fabricating these semiconducting nanotube networks (SWNTnts) can become ineffective if the functionalized surface is not smooth with high amine density. However, by replacing the amine with a nitrile group, SAM formation can be made more controllable and reproducible. Upon SWNT deposition, the nitrile group was found to not only adsorb higher density SWNTnts but also sort the nanotubes efficiently, as shown by micro-Raman spectroscopy. Upon testing these SWNTnts for device performance, these thin-film transistors (TFTs) were also found to yield higher quality devices than those fabricated on amine surfaces. Overall, these results expand the applicability of surface sorting and SWNT adsorption to other organic functionalities for nanotube separation. This report provides an outline of the merits and characterization of using the nitrile functional group for the separation and adsorption of SWNTs and its integration in network TFTs.

  View details for DOI 10.1021/nn300124y

  View details for Web of Science ID 000305661300031

  View details for PubMedID 22588018

• In Situ Hetero End-Functionalized Polythiophene and Subsequent "Click" Chemistry With DNA MACROMOLECULAR RAPID COMMUNICATIONS Lee, J. K., Ko, S., Bao, Z. 2012; 33 (10): 938-942

  Abstract

  It is demonstrated that bifunctionalized polythiophenes involving thiol and azide end-functional groups can be synthesized by chain-growth Suzuki-Miyaura type polymerization. The bifunctionalized polythiophenes are successfully characterized by 1H NMR, gel permeation chromatography (GPC), and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). Furthermore, the azide end-group reacts with DNA via "click chemistry" to form a polythiophene/DNA hybrid structure, which is characterized by ESI-MS. The described synthetic approaches will lead to the synthesis of novel multi-block copolymers as well as biomolecule-based conjugated polymer structures.

  View details for DOI 10.1002/marc.201100686

  View details for PubMedID 22354688

• High-Performance Transistors and Complementary Inverters Based on Solution-Grown Aligned Organic Single-Crystals ADVANCED MATERIALS Li, H., Tee, B. C., Giri, G., Chung, J. W., Lee, S. Y., Bao, Z. 2012; 24 (19): 2588-2591

  View details for DOI 10.1002/adma.201200151

  View details for Web of Science ID 000303795700008

  View details for PubMedID 22461243

• Recent advances in flexible and stretchable electronics, sensors and power sources SCIENCE CHINA-CHEMISTRY Tok, J. B., Bao Zhenan, Z. A. 2012; 55 (5): 718-725

  View details for DOI 10.1007/s11426-012-4503-3

  View details for Web of Science ID 000304248500007

• Graphene-sponges as high-performance low-cost anodes for microbial fuel cells ENERGY & ENVIRONMENTAL SCIENCE Xie, X., Yu, G., Liu, N., Bao, Z., Criddle, C. S., Cui, Y. 2012; 5 (5): 6862-6866

  View details for DOI 10.1039/c2ee03583a

  View details for Web of Science ID 000303251500019

• Organic Transistors with Ordered Nanoparticle Arrays as a Tailorable Platform for Selective, In Situ Detection ACS NANO Hammock, M. L., Sokolov, A. N., Stoltenberg, R. M., Naab, B. D., Bao, Z. 2012; 6 (4): 3100-3108

  Abstract

  The use of organic transistors as sensing platforms provides a number of distinct advantages over conventional detection technologies, including their tunability, portability, and ability to directly transduce binding events without tedious and expensive labeling procedures. However, detection efforts using organic transistors lack a general method to uniquely specify and detect a target of interest. While highly sensitive liquid- and vapor-phase sensors have been previously reported, detection has been restricted either to the serendipitous interaction of the analyte molecules with the organic semiconductor or to the covalent functionalization of the semiconductor with receptor groups to enhance specificity. However, the former technique cannot be regularly relied upon for tailorable sensing while the latter may result in unpredictable decreases in electronic performance. Thus, a method to provide modular receptor sites on the surface of an organic transistor without damaging the device will significantly advance the field, especially regarding biological species detection. In this work, we utilized a block copolymer to template ordered, large-area arrays of gold nanoparticles, with sub-100 nm center-to-center spacing onto the surface of an organic transistor. This highly modular platform is designed for orthogonal modification with a number of available chemical and biological functional groups by taking advantage of the well-studied gold-thiol linkage. Herein, we demonstrate the functionalization of gold nanoparticles with a mercury-binding oligonucleotide sequence. Finally, we demonstrate the highly selective and robust detection of mercury(II) using this platform in an underwater environment.

  View details for DOI 10.1021/nn204830b

  View details for Web of Science ID 000303099300027

  View details for PubMedID 22397363

• Controlled Conjugated Backbone Twisting for an Increased Open-Circuit Voltage while Having a High Short-Circuit Current in Poly(hexylthiophene) Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ko, S., Hoke, E. T., Pandey, L., Hong, S., Mondal, R., Risko, C., Yi, Y., Noriega, R., McGehee, M. D., Bredas, J., Salleo, A., Bao, Z. 2012; 134 (11): 5222-5232

  Abstract

  Conjugated polymers with nearly planar backbones have been the most commonly investigated materials for organic-based electronic devices. More twisted polymer backbones have been shown to achieve larger open-circuit voltages in solar cells, though with decreased short-circuit current densities. We systematically impose twists within a family of poly(hexylthiophene)s and examine their influence on the performance of polymer:fullerene bulk heterojunction (BHJ) solar cells. A simple chemical modification concerning the number and placement of alkyl side chains along the conjugated backbone is used to control the degree of backbone twisting. Density functional theory calculations were carried out on a series of oligothiophene structures to provide insights on how the sterically induced twisting influences the geometric, electronic, and optical properties. Grazing incidence X-ray scattering measurements were performed to investigate how the thin-film packing structure was affected. The open-circuit voltage and charge-transfer state energy of the polymer:fullerene BHJ solar cells increased substantially with the degree of twist induced within the conjugated backbone--due to an increase in the polymer ionization potential--while the short-circuit current decreased as a result of a larger optical gap and lower hole mobility. A controlled, moderate degree of twist along the poly(3,4-dihexyl-2,2':5',2''-terthiophene) (PDHTT) conjugated backbone led to a 19% enhancement in the open-circuit voltage (0.735 V) vs poly(3-hexylthiophene)-based devices, while similar short-circuit current densities, fill factors, and hole-carrier mobilities were maintained. These factors resulted in a power conversion efficiency of 4.2% for a PDHTT:[6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) blend solar cell without thermal annealing. This simple approach reveals a molecular design avenue to increase open-circuit voltage while retaining the short-circuit current.

  View details for DOI 10.1021/ja210954r

  View details for Web of Science ID 000302191900036

  View details for PubMedID 22385287

• 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium Iodide as a New Air-Stable n-Type Dopant for Vacuum-Processed Organic Semiconductor Thin Films JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wei, P., Menke, T., Naab, B. D., Leo, K., Riede, M., Bao, Z. 2012; 134 (9): 3999-4002

  Abstract

  2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I) was synthesized and employed as a strong n-type dopant for fullerene C(60), a well-known n-channel semiconductor. The coevaporated thin films showed a maximum conductivity of 5.5 S/cm at a doping concentration of 8.0 wt% (14 mol%), which is the highest value reported to date for molecular n-type conductors. o-MeO-DMBI-I can be stored and handled in air for extended periods without degradation and is thus promising for various organic electronic devices.

  View details for DOI 10.1021/ja211382x

  View details for PubMedID 22324847

• Contacting nanowires and nanotubes with atomic precision for electronic transport APPLIED PHYSICS LETTERS Qin, S., Hellstrom, S., Bao, Z., Boyanov, B., Li, A. 2012; 100 (10)

  View details for DOI 10.1063/1.3692585

  View details for Web of Science ID 000301655500059

• Chemical and Engineering Approaches To Enable Organic Field-Effect Transistors for Electronic Skin Applications ACCOUNTS OF CHEMICAL RESEARCH Sokolov, A. N., Tee, B. C., Bettinger, C. J., Tok, J. B., Bao, Z. 2012; 45 (3): 361-371

  Abstract

  Skin is the body's largest organ and is responsible for the transduction of a vast amount of information. This conformable material simultaneously collects signals from external stimuli that translate into information such as pressure, pain, and temperature. The development of an electronic material, inspired by the complexity of this organ is a tremendous, unrealized engineering challenge. However, the advent of carbon-based electronics may offer a potential solution to this long-standing problem. In this Account, we describe the use of an organic field-effect transistor (OFET) architecture to transduce mechanical and chemical stimuli into electrical signals. In developing this mimic of human skin, we thought of the sensory elements of the OFET as analogous to the various layers and constituents of skin. In this fashion, each layer of the OFET can be optimized to carry out a specific recognition function. The separation of multimodal sensing among the components of the OFET may be considered a "divide and conquer" approach, where the electronic skin (e-skin) can take advantage of the optimized chemistry and materials properties of each layer. This design of a novel microstructured gate dielectric has led to unprecedented sensitivity for tactile pressure events. Typically, pressure-sensitive components within electronic configurations have suffered from a lack of sensitivity or long mechanical relaxation times often associated with elastomeric materials. Within our method, these components are directly compatible with OFETs and have achieved the highest reported sensitivity to date. Moreover, the tactile sensors operate on a time scale comparable with human skin, making them ideal candidates for integration as synthetic skin devices. The methodology is compatible with large-scale fabrication and employs simple, commercially available elastomers. The design of materials within the semiconductor layer has led to the incorporation of selectivity and sensitivity within gas-sensing devices and has enabled stable sensor operation within aqueous media. Furthermore, careful tuning of the chemical composition of the dielectric layer has provided a means to operate the sensor in real time within an aqueous environment and without the need for encapsulation layers. The integration of such devices as electronic mimics of skin will require the incorporation of biocompatible or biodegradable components. Toward this goal, OFETs may be fabricated with >99% biodegradable components by weight, and the devices are robust and stable, even in aqueous environments. Collectively, progress to date suggests that OFETs may be integrated within a single substrate to function as an electronic mimic of human skin, which could enable a large range of sensing-related applications from novel prosthetics to robotic surgery.

  View details for DOI 10.1021/ar2001233

  View details for Web of Science ID 000302033000005

  View details for PubMedID 21995646

• The effect of pH and DNA concentration on organic thin-film transistor biosensors ORGANIC ELECTRONICS Khan, H. U., Roberts, M. E., Johnson, O., Knoll, W., Bao, Z. 2012; 13 (3): 519-524

  View details for DOI 10.1016/j.orgel.2011.12.013

  View details for Web of Science ID 000300392100024

• Highly Effective Separation of Semiconducting Carbon Nanotubes verified via Short-Channel Devices Fabricated Using Dip-Pen Nanolithography ACS NANO Park, S., Lee, H. W., Wang, H., Selvarasah, S., Dokmeci, M. R., Park, Y. J., Cha, S. N., Kim, J. M., Bao, Z. 2012; 6 (3): 2487-2496

  Abstract

  We have verified a highly effective separation of semiconducting single-walled carbon nanotubes (sc-SWNTs) via statistical analysis of short-channel devices fabricated using multipen dip-pen nanolithography. Our SWNT separation technique utilizes a polymer (rr-P3DDT) that selectively interacts with and disperses sc-SWNTs. Our devices had channel lengths on the order of 300-500 nm, with an average of about 3 SWNTs that directly connected the source-drain electrodes. A total of 140 SWNTs were characterized, through which we have observed that all of the SWNTs exhibited semiconducting behavior with an average on/off current ratio of ~10(6). Additionally, we have characterized 50 SWNTs after the removal of rr-P3DDT, through which we have again observed semiconducting behavior for all of the SWNTs with similar electrical characteristics. The relatively low average on-conductance of 0.0796 μS was attributed to the distribution of small diameter SWNTs in our system and due to the non-ohmic Au contacts on SWNTs. The largely positive threshold voltages were shifted toward zero after vacuum annealing, indicating that the SWNTs were doped in air. To the best of our knowledge, this is the first time numerous SWNTs were electrically characterized using short-channel devices, through which all of the measured SWNTs were determined to be semiconducting. Hence, our semiconducting single-walled carbon nanotube sorting system holds a great deal of promise in bringing forth a variety of practical applications in SWNT electronics.

  View details for DOI 10.1021/nn204875a

  View details for PubMedID 22352426

• High-Mobility Field-Effect Transistors from Large-Area Solution-Grown Aligned C-60 Single Crystals JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, H., Tee, B. C., Cha, J. J., Cui, Y., Chung, J. W., Lee, S. Y., Bao, Z. 2012; 134 (5): 2760-2765

  Abstract

  Field-effect transistors based on single crystals of organic semiconductors have the highest reported charge carrier mobility among organic materials, demonstrating great potential of organic semiconductors for electronic applications. However, single-crystal devices are difficult to fabricate. One of the biggest challenges is to prepare dense arrays of single crystals over large-area substrates with controlled alignment. Here, we describe a solution processing method to grow large arrays of aligned C(60) single crystals. Our well-aligned C(60) single-crystal needles and ribbons show electron mobility as high as 11 cm(2)V(-1)s(-1) (average mobility: 5.2 ± 2.1 cm(2)V(-1)s(-1) from needles; 3.0 ± 0.87 cm(2)V(-1)s(-1) from ribbons). This observed mobility is ~8-fold higher than the maximum reported mobility for solution-grown n-channel organic materials (1.5 cm(2)V(-1)s(-1)) and is ~2-fold higher than the highest mobility of any n-channel organic material (~6 cm(2)V(-1)s(-1)). Furthermore, our deposition method is scalable to a 100 mm wafer substrate, with around 50% of the wafer surface covered by aligned crystals. Hence, our method facilitates the fabrication of large amounts of high-quality semiconductor crystals for fundamental studies, and with substantial improvement on the surface coverage of crystals, this method might be suitable for large-area applications based on single crystals of organic semiconductors.

  View details for DOI 10.1021/ja210430b

  View details for Web of Science ID 000300460600049

  View details for PubMedID 22239604

• Fabrication of organic semiconductor crystalline thin films and crystals from solution by confined crystallization ORGANIC ELECTRONICS Akkerman, H. B., Chang, A. C., Verploegen, E., Bettinger, C. J., Toney, M. F., Bao, Z. 2012; 13 (2): 235-243

  View details for DOI 10.1016/j.orgel.2011.11.005

  View details for Web of Science ID 000299539100004

• Highly Conductive and Transparent PEDOT:PSS Films with a Fluorosurfactant for Stretchable and Flexible Transparent Electrodes ADVANCED FUNCTIONAL MATERIALS Vosgueritchian, M., Lipomi, D. J., Bao, Z. 2012; 22 (2): 421-428

  View details for DOI 10.1002/adfm.201101775

  View details for Web of Science ID 000299251800021

• Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates CHEMISTRY OF MATERIALS Lipomi, D. J., Lee, J. A., Vosgueritchian, M., Tee, B. C., Bolander, J. A., Bao, Z. 2012; 24 (2): 373-382

  View details for DOI 10.1021/cm203216m

  View details for Web of Science ID 000299367500018

• Micro-imprinted prism substrate for self-aligned short channel organic transistors on a flexible substrate APPLIED PHYSICS LETTERS Jeon, J., Tee, B. C., Murmann, B., Bao, Z. 2012; 100 (4)

  View details for DOI 10.1063/1.3679119

  View details for Web of Science ID 000300064500064

• Mechanistic Considerations of Bending-Strain Effects within Organic Semiconductors on Polymer Dielectrics ADVANCED FUNCTIONAL MATERIALS Sokolov, A. N., Cao, Y., Johnson, O. B., Bao, Z. 2012; 22 (1): 175-183

  View details for DOI 10.1002/adfm.201101418

  View details for Web of Science ID 000298673500021

• Wafer-Scale Fabrication and Characterization of Thin-Film Transistors with Polythiophene-Sorted Semiconducting Carbon Nanotube Networks ACS NANO Liyanage, L. S., Lee, H., Patil, N., Park, S., Mitra, S., Bao, Z., Wong, H. P. 2012; 6 (1): 451-458

  Abstract

  Semiconducting single-walled carbon nanotubes (SWCNTs) have great potential of becoming the channel material for future thin-film transistor technology. However, an effective sorting technique is needed to obtain high-quality semiconducting SWCNTs for optimal device performance. In our previous work, we reported a dispersion technique for semiconducting SWCNTs that relies on regioregular poly(3-dodecylthiophene) (rr-P3DDT) to form hybrid nanostructures. In this study, we demonstrate the scalability of those sorted CNT composite structures to form arrays of TFTs using standard lithographic techniques. The robustness of these CNT nanostructures was tested with Raman spectroscopy and atomic force microscope images. Important trends in device properties were extracted by means of electrical measurements for different CNT concentrations and channel lengths (L(c)). A statistical study provided an average mobility of 1 cm(2)/V·s and I(on)/I(off) as high as 10(6) for short channel lengths (L(c) = 1.5 μm) with 100% yield. This highlights the effectiveness of this sorting technique and its scalability for large-scale, flexible, and transparent display applications.

  View details for DOI 10.1021/nn203771u

  View details for PubMedID 22148677

• 5,11-Conjugation-extended low-bandgap anthradithiophene-containing polymer exhibiting enhanced thin-film order and field-effect mobility CHEMICAL COMMUNICATIONS Jiang, Y., Mei, J., Ayzner, A. L., Toney, M. F., Bao, Z. 2012; 48 (58): 7286-7288

  Abstract

  Anthradithiophene was incorporated in a polymer structure by extending its conjugation from the 5,11-positions, through in situ desilylation followed by acetylenic coupling with a dibromo-monomer. The resulting polymer showed largely redshifted order in a thin film as well as order in thin film, forming lamellar structures out of the substrate plane. As a result, it exhibits field-effect hole mobilities, on the order of 0.1 cm(2) V(-1) s(-1), a ten to hundred-fold improvement as compared to previous acene-containing polymers.

  View details for DOI 10.1039/c2cc32473c

  View details for Web of Science ID 000305624500018

  View details for PubMedID 22699310

• Themed issue on "organic optoelectronic materials'' JOURNAL OF MATERIALS CHEMISTRY Hu, W., Bao, Z., Muellen, K. 2012; 22 (10): 4134-4135

  View details for DOI 10.1039/c1jm90199k

  View details for Web of Science ID 000300250200001

• Impact of regioregularity on thin-film transistor and photovoltaic cell performances of pentacene-containing polymers JOURNAL OF MATERIALS CHEMISTRY Jiang, Y., Hong, S., Oh, J. H., Mondal, R., Okamoto, T., Verploegen, E., Toney, M. F., McGehee, M. D., Bao, Z. 2012; 22 (10): 4356-4363

  View details for DOI 10.1039/c2jm15483h

  View details for Web of Science ID 000300250200027

• Tuning charge transport in solution-sheared organic semiconductors using lattice strain NATURE Giri, G., Verploegen, E., Mannsfeld, S. C., Atahan-Evrenk, S., Kim, D. H., Lee, S. Y., Becerril, H. A., Aspuru-Guzik, A., Toney, M. F., Bao, Z. 2011; 480 (7378): 504-U124

  Abstract

  Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π-π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π-π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 Å to 3.08 Å. We believe that 3.08 Å is the shortest π-π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π-π distance of 3.04 Å has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm(2) V(-1) s(-1) for unstrained films to a high mobility of 4.6 cm(2) V(-1) s(-1) for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.

  View details for DOI 10.1038/nature10683

  View details for PubMedID 22193105

• Siloxane-Terminated Solubilizing Side Chains: Bringing Conjugated Polymer Backbones Closer and Boosting Hole Mobilities in Thin-Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mei, J., Kim, D. H., Ayzner, A. L., Toney, M. F., Bao, Z. 2011; 133 (50): 20130-20133

  Abstract

  We introduce a novel siloxane-terminated solubilizing group and demonstrate its effectiveness as a side chain in an isoindigo-based conjugated polymer. An average hole mobility of 2.00 cm(2) V(-1) s(-1) (with a maximum mobility of 2.48 cm(2) V(-1) s(-1)), was obtained from solution-processed thin-film transistors, one of the highest mobilities reported to date. In contrast, the reference polymer with a branched alkyl side chain gave an average hole mobility of 0.30 cm(2) V(-1) s(-1) and a maximum mobility of 0.57 cm(2) V(-1) s(-1). This is largely explained by the polymer packing: our new polymer exhibited a π-π stacking distance of 3.58 Å, while the reference polymer showed a distance of 3.76 Å.

  View details for DOI 10.1021/ja209328m

  View details for Web of Science ID 000298713600028

  View details for PubMedID 22122218

• Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes NATURE NANOTECHNOLOGY Lipomi, D. J., Vosgueritchian, M., Tee, B. C., Hellstrom, S. L., Lee, J. A., Fox, C. H., Bao, Z. 2011; 6 (12): 788-792

  Abstract

  Transparent, elastic conductors are essential components of electronic and optoelectronic devices that facilitate human interaction and biofeedback, such as interactive electronics, implantable medical devices and robotic systems with human-like sensing capabilities. The availability of conducting thin films with these properties could lead to the development of skin-like sensors that stretch reversibly, sense pressure (not just touch), bend into hairpin turns, integrate with collapsible, stretchable and mechanically robust displays and solar cells, and also wrap around non-planar and biological surfaces such as skin and organs, without wrinkling. We report transparent, conducting spray-deposited films of single-walled carbon nanotubes that can be rendered stretchable by applying strain along each axis, and then releasing this strain. This process produces spring-like structures in the nanotubes that accommodate strains of up to 150% and demonstrate conductivities as high as 2,200 S cm(-1) in the stretched state. We also use the nanotube films as electrodes in arrays of transparent, stretchable capacitors, which behave as pressure and strain sensors.

  View details for DOI 10.1038/NNANO.2011.184

  View details for Web of Science ID 000298248300011

  View details for PubMedID 22020121

• A Cell-Compatible Conductive Film from a Carbon Nanotube Network Adsorbed on Poly-L-lysine ACS NANO Lin, D. W., Bettinger, C. J., Ferreira, J. P., Wang, C. L., Bao, Z. 2011; 5 (12): 10026-10032

  Abstract

  Single-walled carbon nanotubes (SWNTs) have shown promise for use in organic electronic applications including thin film transistors, conducting electrodes, and biosensors. Additionally, previous studies found applications for SWNTs in bioelectronic devices, including drug delivery carriers and scaffolds for tissue engineering. There is a current need to rapidly process SWNTs from solution phase to substrates in order to produce device structures that are also biocompatible. Studies have shown the use of surfaces covalently functionalized with primary amines to selectively adsorb semiconducting SWNTs. Here we report the potential of substrates modified with physisorbed polymers as a rapid biomaterials-based approach for the formation of SWNT networks. We hypothesized that rapid surface modification could be accomplished by adsorption of poly-L-lysine (PLL), which is also frequently used in biological applications. We detail a rapid and facile method for depositing SWNTs onto various substrate materials using the amine-rich PLL. Dispersions of SWNTs of different chiralities suspended in N-methylpyrrolidinone (NMP) were spin coated onto various PLL-treated substrates. SWNT adsorption and alignment were characterized by atomic force microscopy (AFM) while electrical properties of the network were characterized by 2-terminal resistance measurements. Additionally, we investigated the relative chirality of the SWNT networks by micro-Raman spectroscopy. The SWNT surface density was strongly dependent upon the adsorbed concentration of PLL on the surface. SWNT adsorbed on PLL-treated substrates exhibited enhanced biocompatibility compared to SWNT networks fabricated using alternative methods such as drop casting. These results suggest that PLL films can promote formation of biocompatible SWNT networks for potential biomedical applications.

  View details for DOI 10.1021/nn203870c

  View details for Web of Science ID 000298316700079

  View details for PubMedID 22053708

• High-Mobility Air-Stable Solution-Shear-Processed n-Channel Organic Transistors Based on Core-Chlorinated Naphthalene Diimides ADVANCED FUNCTIONAL MATERIALS Lee, W., Oh, J. H., Suraru, S., Chen, W., Wuerthner, F., Bao, Z. 2011; 21 (21): 4173-4181

  View details for DOI 10.1002/adfm.201101606

  View details for Web of Science ID 000297096900021

• Selective dispersion of high purity semiconducting single-walled carbon nanotubes with regioregular poly(3-alkylthiophene)s NATURE COMMUNICATIONS Lee, H. W., Yoon, Y., Park, S., Oh, J. H., Hong, S., Liyanage, L. S., Wang, H., Morishita, S., Patil, N., Park, Y. J., Park, J. J., Spakowitz, A., Galli, G., Gygi, F., Wong, P. H., Tok, J. B., Kim, J. M., Bao, Z. 2011; 2

  Abstract

  Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around SWNTs. However, no sorting of sc-SWNTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-SWNTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-SWNTs. Our approach enables direct film preparation after a simple centrifugation step. Using the sorted sc-SWNTs, we fabricate high-performance SWNT network transistors with observed charge-carrier mobility as high as 12 cm(2) V(-1) s(-1) and on/off ratio of >10(6). Our method offers a facile and a scalable route for separating sc-SWNTs and fabrication of electronic devices.

  View details for DOI 10.1038/ncomms1545

  View details for PubMedID 22086341

• Carrier mobility in pentacene as a function of grain size and orientation derived from scanning transmission X-ray microscopy ORGANIC ELECTRONICS Braeuer, B., Kukreja, R., Virkar, A., Akkerman, H. B., Fognini, A., Tyliszczak, T., Bao, Z. 2011; 12 (11): 1936-1942

  View details for DOI 10.1016/j.orgel.2011.08.007

  View details for Web of Science ID 000295830700029

• Improving the Performance of Lithium-Sulfur Batteries by Conductive Polymer Coating ACS NANO Yang, Y., Yu, G., Cha, J. J., Wu, H., Vosgueritchian, M., Yao, Y., Bao, Z., Cui, Y. 2011; 5 (11): 9187-9193

  View details for DOI 10.1021/nn203436j

  View details for PubMedID 21995642

• 3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ko, S., Verploegen, E., Hong, S., Mondal, R., Hoke, E. T., Toney, M. F., McGehee, M. D., Bao, Z. 2011; 133 (42): 16722-16725

  Abstract

  We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.

  View details for DOI 10.1021/ja207429s

  View details for Web of Science ID 000296678200004

  View details for PubMedID 21970371

• Enhancing the Supercapacitor Performance of Graphene/MnO2 Nanostructured Electrodes by Conductive Wrapping NANO LETTERS Yu, G., Hu, L., Liu, N., Wang, H., Vosgueritchian, M., Yang, Y., Cui, Y., Bao, Z. 2011; 11 (10): 4438-4442

  Abstract

  MnO2 is considered one of the most promising pseudocapactive materials for high-performance supercapacitors given its high theoretical specific capacitance, low-cost, environmental benignity, and natural abundance. However, MnO2 electrodes often suffer from poor electronic and ionic conductivities, resulting in their limited performance in power density and cycling. Here we developed a "conductive wrapping" method to greatly improve the supercapacitor performance of graphene/MnO2-based nanostructured electrodes. By three-dimensional (3D) conductive wrapping of graphene/MnO2 nanostructures with carbon nanotubes or conducting polymer, specific capacitance of the electrodes (considering total mass of active materials) has substantially increased by ∼20% and ∼45%, respectively, with values as high as ∼380 F/g achieved. Moreover, these ternary composite electrodes have also exhibited excellent cycling performance with >95% capacitance retention over 3000 cycles. This 3D conductive wrapping approach represents an exciting direction for enhancing the device performance of metal oxide-based electrochemical supercapacitors and can be generalized for designing next-generation high-performance energy storage devices.

  View details for DOI 10.1021/nl2026635

  View details for PubMedID 21942427

• Stretchable, elastic materials and devices for solar energy conversion ENERGY & ENVIRONMENTAL SCIENCE Lipomi, D. J., Bao, Z. 2011; 4 (9): 3314-3328

  View details for DOI 10.1039/c1ee01881g

  View details for Web of Science ID 000294306900015

• From computational discovery to experimental characterization of a high hole mobility organic crystal NATURE COMMUNICATIONS Sokolov, A. N., Atahan-Evrenk, S., Mondal, R., Akkerman, H. B., Sanchez-Carrera, R. S., Granados-Focil, S., Schrier, J., Mannsfeld, S. C., Zoombelt, A. P., Bao, Z., Aspuru-Guzik, A. 2011; 2

  Abstract

  For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm(2) V(-1) s(-1), respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm(2) V(-1) s(-1) reported to date.

  View details for DOI 10.1038/ncomms1451

  View details for Web of Science ID 000294806500030

  View details for PubMedID 21847111

  View details for PubMedCentralID PMC3366639

• Solution-Processed Graphene/MnO2 Nanostructured Textiles for High-Performance Electrochemical Capacitors NANO LETTERS Yu, G., Hu, L., Vosgueritchian, M., Wang, H., Xie, X., McDonough, J. R., Cui, X., Cui, Y., Bao, Z. 2011; 11 (7): 2905-2911

  Abstract

  Large scale energy storage system with low cost, high power, and long cycle life is crucial for addressing the energy problem when connected with renewable energy production. To realize grid-scale applications of the energy storage devices, there remain several key issues including the development of low-cost, high-performance materials that are environmentally friendly and compatible with low-temperature and large-scale processing. In this report, we demonstrate that solution-exfoliated graphene nanosheets (∼5 nm thickness) can be conformably coated from solution on three-dimensional, porous textiles support structures for high loading of active electrode materials and to facilitate the access of electrolytes to those materials. With further controlled electrodeposition of pseudocapacitive MnO(2) nanomaterials, the hybrid graphene/MnO(2)-based textile yields high-capacitance performance with specific capacitance up to 315 F/g achieved. Moreover, we have successfully fabricated asymmetric electrochemical capacitors with graphene/MnO(2)-textile as the positive electrode and single-walled carbon nanotubes (SWNTs)-textile as the negative electrode in an aqueous Na(2)SO(4) electrolyte solution. These devices exhibit promising characteristics with a maximum power density of 110 kW/kg, an energy density of 12.5 Wh/kg, and excellent cycling performance of ∼95% capacitance retention over 5000 cycles. Such low-cost, high-performance energy textiles based on solution-processed graphene/MnO(2) hierarchical nanostructures offer great promise in large-scale energy storage device applications.

  View details for DOI 10.1021/nl2013828

  View details for PubMedID 21667923

• Stretchable Organic Solar Cells ADVANCED MATERIALS Lipomi, D. J., Tee, B. C., Vosgueritchian, M., Bao, Z. 2011; 23 (15): 1771-?

  View details for DOI 10.1002/adma.201004426

  View details for Web of Science ID 000289531800014

  View details for PubMedID 21491510

• Aryl-Perfluoroaryl Substituted Tetracene: Induction of Face-to-Face pi-pi Stacking and Enhancement of Charge Carrier Properties CHEMISTRY OF MATERIALS Okamoto, T., Nakahara, K., Saeki, A., Seki, S., Oh, J. H., Akkerman, H. B., Bao, Z., Matsuo, Y. 2011; 23 (7): 1646-1649

  View details for DOI 10.1021/cm200356y

  View details for Web of Science ID 000289029400004

• Pentacene Based Organic Thin Film Transistors as the Transducer for Biochemical Sensing in Aqueous Media CHEMISTRY OF MATERIALS Khan, H. U., Roberts, M. E., Knoll, W., Bao, Z. 2011; 23 (7): 1946-1953

  View details for DOI 10.1021/cm103685c

  View details for Web of Science ID 000289029400039

• The Phase Behavior of a Polymer-Fullerene Bulk Heterojunction System that Contains Bimolecular Crystals JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS Miller, N. C., Gysel, R., Miller, C. E., Verploegen, E., Beiley, Z., Heeney, M., McCulloch, I., Bao, Z., Toney, M. F., McGehee, M. D. 2011; 49 (7): 499-503

  View details for DOI 10.1002/polb.22214

  View details for Web of Science ID 000288541400003

• Solution-Shear-Processed Quaterrylene Diimide Thin-Film Transistors Prepared by Pressure-Assisted Thermal Cleavage of Swallow Tails JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Oh, J. H., Lee, W., Noe, T., Chen, W., Koenemann, M., Bao, Z. 2011; 133 (12): 4204-4207

  Abstract

  A scalable synthesis of swallow-tailed quaterrylene diimides (STQDIs) and a method for the solution processing of sparingly soluble quaterrylene diimide (QDI) thin films are described. The pressure-assisted thermal cleavage of swallow tails yields crystalline QDI layers with electron mobility up to 0.088 cm(2) V(-1) s(-1). The developed method opens up a new route toward the solution processing of higher rylene diimides with poor solubility.

  View details for DOI 10.1021/ja110486s

  View details for Web of Science ID 000291715300015

  View details for PubMedID 21375243

• The effect of amine protonation on the electrical properties of spin-assembled single-walled carbon nanotube networks NANOTECHNOLOGY Opatkiewicz, J. P., LeMieux, M. C., Patil, N. P., Wei, H., Mitra, S., Bao, Z. 2011; 22 (12)

  Abstract

  Amine-terminated self-assembled monolayers (SAMs) have been shown to selectively adsorb semiconducting single-walled carbon nanotubes (sc-SWNTs). Previous studies have shown that when deposited by spin coating, the resulting nanotube networks (SWNTnts) can be strongly influenced by the charge state of the amine (primary, secondary, and tertiary). When the amine surfaces were exposed to varying pH solutions, the conductivity and overall quality of the resulting fabricated networks were altered. Atomic force microscopy (AFM) topography had shown that the density of the SWNTnts was reduced as the amine protonation decreased, indicating that the electrostatic attraction between the SWNTs in solution and the surface influenced the adsorption. Simultaneously, μ-Raman analysis had suggested that when exposed to more basic conditions, the resulting networks were enhanced with sc-SWNTs. To directly confirm this enhancement, Ti/Pd contacts were deposited and devices were tested in air. Key device characteristics were found to match the enhancement trends previously observed by spectroscopy. For the primary and secondary amines, on/off current ratios were commensurate with the Raman trends in metallic contribution, while no trends were observed on the tertiary amine (due to weaker interactions). Finally, differing SWNT solution volumes were used to compensate for adsorption differences and yielded identical SWNTnt densities on the various pH-treated samples to eliminate the influence of network density. These results further the understanding of the amine-SWNT interaction during the spin coating process. Overall, we provide a convenient route to provide SWNT-based TFTs with highly tunable electronic charge transport through better understanding of the influence of these specific interactions.

  View details for DOI 10.1088/0957-4484/22/12/125201

  View details for Web of Science ID 000287448200001

  View details for PubMedID 21317495

• Microfluidic Arrays for Rapid Characterization of Organic Thin-Film Transistor Performance ADVANCED MATERIALS Bettinger, C. J., Becerril, H. A., Kim, D. H., Lee, B., Lee, S., Bao, Z. 2011; 23 (10): 1257-?

  View details for DOI 10.1002/adma.201003815

  View details for Web of Science ID 000288170700010

  View details for PubMedID 21381125

• Syntheses of Organic Molecule-DNA Hybrid Structures ACS NANO Lee, J. K., Jung, Y. H., Tok, J. B., Bao, Z. 2011; 5 (3): 2067-2074

  Abstract

  Investigation of robust and efficient pathways to build DNA-organic molecule hybrid structures is fundamentally important to realize controlled placement of single molecules for potential applications, such as single-molecule electronic devices. Herein, we report a systematic investigation of synthetic processes for preparing organic molecule-DNA building blocks and their subsequent elongation to generate precise micrometer-sized structures. Specifically, optimal cross-coupling routes were identified to enable chemical linkages between three different organic molecules, namely, polyethylene glycol (PEG), poly(p-phenylene ethynylene) (PPE), and benzenetricarboxylate, with single-stranded (ss) DNA. The resulting DNA-organic molecule hybrid building blocks were purified and characterized by both denaturing gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS). The building blocks were subsequently elongated through both the DNA hybridization and ligation processes to prepare micrometer-sized double-stranded (ds) DNA-organic molecule hybrid structures. The described synthetic procedures should facilitate future syntheses of various hybrid DNA-based organic molecular structures.

  View details for DOI 10.1021/nn1032455

  View details for PubMedID 21323343

• Controlling Electric Dipoles in Nanodielectrics and Its Applications for Enabling Air-Stable n-Channel Organic Transistors NANO LETTERS Chung, Y., Verploegen, E., Vailionis, A., Sun, Y., Nishi, Y., Murmann, B., Bao, Z. 2011; 11 (3): 1161-1165

  Abstract

  We present a new method to manipulate the channel charge density of field-effect transistors using dipole-generating self-assembled monolayers (SAMs) with different anchor groups. Our approach maintains an ideal interface between the dipole layers and the semiconductor while changing the built-in electric potential by 0.41-0.50 V. This potential difference can be used to change effectively the electrical properties of nanoelectronic devices. We further demonstrate the application of the SAM dipoles to enable air-stable operation of n-channel organic transistors.

  View details for DOI 10.1021/nl104087u

  View details for Web of Science ID 000288061500043

  View details for PubMedID 21323381

• Halogenated Materials as Organic Semiconductors CHEMISTRY OF MATERIALS Tang, M. L., Bao, Z. 2011; 23 (3): 446-455

  View details for DOI 10.1021/cm102182x

  View details for Web of Science ID 000286691100010

• Selective Surface Chemistry Using Alumina Nanoparticles Generated from Block Copolymers LANGMUIR Stoltenberg, R. M., Liu, C., Bao, Z. 2011; 27 (1): 445-451

  Abstract

  Developing orthogonal surface chemistry techniques that perform at the nanoscale is key to achieving precise control over molecular patterning on surfaces. We report the formation and selective functionalization of alumina nanoparticle arrays generated from block copolymer templates. This new material provides an alternative to gold for orthogonal surface chemistry at the nanometer scale. Atomic force microscopy and X-ray photoelectron spectroscopy confirm these particles show excellent selectivity over silica for phosphonic and carboxylic acid adsorption. As this is the first reported synthesis of alumina nanoparticles from block copolymer templates, characterizations via Fourier transform infrared spectroscopy, Auger electron spectroscopy, and transmission electron microscopy are presented. Reproducible formation of alumina nanoparticles was dependent on a counterintuitive synthetic step wherein a small amount of water is added to an anhydrous toluene solution of block copolymer and aluminum chloride. The oxidation environment of the aluminum in these particles, as measured by Auger electron spectroscopy, is similar to that of native aluminum oxide and alumina grown by atomic layer deposition. This discovery expands the library of available surface chemistries for nanoscale molecular patterning.

  View details for DOI 10.1021/la104094h

  View details for Web of Science ID 000285560400060

  View details for PubMedID 21133369

• Thin Film Structure of Triisopropylsilylethynyl-Functionalized Pentacene and Tetraceno[2,3-b]thiophene from Grazing Incidence X-Ray Diffraction ADVANCED MATERIALS Mannsfeld, S. C., Tang, M. L., Bao, Z. 2011; 23 (1): 127-?

  View details for DOI 10.1002/adma.201003135

  View details for Web of Science ID 000285723400015

  View details for PubMedID 21104808

• The Shear Flow Processing of Controlled DNA Tethering and Stretching for Organic Molecular Electronics ACS NANO Yu, G., Kushwaha, A., Lee, J. K., Shaqfeh, E. S., Bao, Z. 2011; 5 (1): 275-282

  Abstract

  DNA has been recently explored as a powerful tool for developing molecular scaffolds for making reproducible and reliable metal contacts to single organic semiconducting molecules. A critical step in the process of exploiting DNA-organic molecule-DNA (DOD) array structures is the controlled tethering and stretching of DNA molecules. Here we report the development of reproducible surface chemistry for tethering DNA molecules at tunable density and demonstrate shear flow processing as a rationally controlled approach for stretching/aligning DNA molecules of various lengths. Through enzymatic cleavage of λ-phage DNA to yield a series of DNA chains of various lengths from 17.3 μm down to 4.2 μm, we have investigated the flow/extension behavior of these tethered DNA molecules under different flow strengths in the flow-gradient plane. We compared Brownian dynamic simulations for the flow dynamics of tethered λ-DNA in shear, and found our flow-gradient plane experimental results matched well with our bead-spring simulations. The shear flow processing demonstrated in our studies represents a controllable approach for tethering and stretching DNA molecules of various lengths. Together with further metallization of DNA chains within DOD structures, this bottom-up approach can potentially enable efficient and reliable fabrication of large-scale nanoelectronic devices based on single organic molecules, therefore opening opportunities in both fundamental understanding of charge transport at the single molecular level and many exciting applications for ever-shrinking molecular circuits.

  View details for DOI 10.1021/nn102669b

  View details for PubMedID 21126082

• High Mobility Air-Stable Solution-Shear-Processed n-Channel Organic Transistors Based on Core-Chlorinated Naphthalene Diimides Adv. Funct. Mater. Lee, W.-Y., Oh, J., H., Suraru, S., Chen, W.-C, Würthner, F., Bao, Z. 2011; 21: 4173-4181
• Solvent additives and their effects on blend morphologies of bulk heterojunctions JOURNAL OF MATERIALS CHEMISTRY Salim, T., Wong, L. H., Braeuer, B., Kukreja, R., Foo, Y. L., Bao, Z., Lam, Y. M. 2011; 21 (1): 242-250

  View details for DOI 10.1039/c0jm01976c

  View details for Web of Science ID 000285067300031

• Side chain engineering of fused aromatic thienopyrazine based low band-gap polymers for enhanced charge carrier mobility JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Verploegen, E., Becerril, H. A., Toney, M. F., Bao, Z. 2011; 21 (5): 1537-1543

  View details for DOI 10.1039/c0jm02491k

  View details for Web of Science ID 000286332000032

• Synthesis of regioregular pentacene-containing conjugated polymers JOURNAL OF MATERIALS CHEMISTRY Okamoto, T., Jiang, Y., Becerril, H. A., Hong, S., Senatore, M. L., Tang, M. L., Toney, M. F., Siegrist, T., Bao, Z. 2011; 21 (20): 7078-7081

  View details for DOI 10.1039/c1jm10643k

  View details for Web of Science ID 000290167200006

• Molecular n-type doping for air-stable electron transport in vacuum-processed n-channel organic transistors APPLIED PHYSICS LETTERS Oh, J. H., Wei, P., Bao, Z. 2010; 97 (24)

  View details for DOI 10.1063/1.3527972

  View details for Web of Science ID 000285481000079

• 2,9-Dibromopentacene: Synthesis and the role of substituent and symmetry on solid-state order SYNTHETIC METALS Okamoto, T., Reese, C., Senatore, M. L., Tang, M. L., Jiang, Y., Parkin, S. R., Bao, Z. 2010; 160 (23-24): 2447-2451

  View details for DOI 10.1016/j.synthmet.2010.09.025

  View details for Web of Science ID 000286910000011

• Full-Swing and High-Gain Pentacene Logic Circuits on Plastic Substrate IEEE ELECTRON DEVICE LETTERS Jeon, J., Murmann, B., Bao, Z. 2010; 31 (12): 1488-1490

  View details for DOI 10.1109/LED.2010.2081336

  View details for Web of Science ID 000284541400044

• Fabrication and Evaluation of Solution-Processed Reduced Graphene Oxide Electrodes for p- and n-Channel Bottom-Contact Organic Thin-Film Transistors ACS NANO Becerril, H. A., Stoltenberg, R. M., Tang, M. L., Roberts, M. E., Liu, Z., Chen, Y., Kim, D. H., Lee, B., Lee, S., Bao, Z. 2010; 4 (11): 6343-6352

  Abstract

  Reduced graphene oxide (RGO) is an electrically conductive carbon-based nanomaterial that has recently attracted attention as a potential electrode for organic electronics. Here we evaluate several solution-based methods for fabricating RGO bottom-contact (BC) electrodes for organic thin-film transistors (OTFTs), demonstrate functional p- and n-channel devices with such electrodes, and compare their electrical performance with analogous devices containing gold electrodes. We show that the morphology of organic semiconductor films deposited on RGO electrodes is similar to that observed in the channel region of the devices and that devices fabricated with RGO electrodes have lower contact resistances compared to those fabricated with gold contacts. Although the conductivity of RGO is poor compared to that of gold, RGO is still an enticing electrode material for organic electronic devices possibly owing to the retention of desirable morphological features, lower contact resistance, lower cost, and solution processability.

  View details for DOI 10.1021/nn101369j

  View details for Web of Science ID 000284438000008

  View details for PubMedID 20945927

• Dip-Pen Nanolithography of Electrical Contacts to Single Graphene Flakes ACS NANO Wang, W. M., Stander, N., Stoltenberg, R. M., Goldhaber-Gordon, D., Bao, Z. 2010; 4 (11): 6409-6416

  Abstract

  This study evaluates an alternative to electron-beam lithography for fabricating nanoscale graphene devices. Dip-pen nanolithography is used for defining monolayer graphene flakes and for patterning of gold electrodes through writing of an alkylthiol on thin films of gold evaporated onto graphene flakes. A wet gold etching step was used to form the individual devices. The sheet resistances of these monolayer graphene devices are comparable to reported literature values. This alternative technique for making electrical contact to 2D nanostructures provides a platform for fundamental studies of nanomaterial properties. The merits of using dip-pen nanolithography include lack of electron-beam irradiation damage and targeted patterning of individual devices with imaging and writing conducted in the same instrument under ambient conditions.

  View details for DOI 10.1021/nn101324x

  View details for Web of Science ID 000284438000015

  View details for PubMedID 20945878

• In Situ, Label-Free DNA Detection Using Organic Transistor Sensors ADVANCED MATERIALS Khan, H. U., Roberts, M. E., Johnson, O., Foerch, R., Knoll, W., Bao, Z. 2010; 22 (40): 4452-4456

  View details for DOI 10.1002/adma.201000790

  View details for Web of Science ID 000284000900003

  View details for PubMedID 20859935

• Effects of Thermal Annealing Upon the Morphology of Polymer-Fullerene Blends ADVANCED FUNCTIONAL MATERIALS Verploegen, E., Mondal, R., Bettinger, C. J., Sok, S., Toney, M. F., Bao, Z. 2010; 20 (20): 3519-3529

  View details for DOI 10.1002/adfm.201000975

  View details for Web of Science ID 000284000200013

• Synthesis and characterization of soluble indolo[3,2-b]carbazole derivatives for organic field-effect transistors ORGANIC ELECTRONICS Boudreault, P. T., Virkar, A. A., Bao, Z., Leclerc, M. 2010; 11 (10): 1649-1659

  View details for DOI 10.1016/j.orgel.2010.07.011

  View details for Web of Science ID 000281624700008

• Effect of Surface Chemistry on Electronic Properties of Carbon Nanotube Network Thin Film Transistors ACS NANO Vosgueritchian, M., LeMieux, M. C., Dodge, D., Bao, Z. 2010; 4 (10): 6137-6145

  Abstract

  Thin films of single-walled carbon nanotubes (SWNTs) are a viable nanomaterial for next generation sensors, transistors, and electrodes for solar cells and displays. Despite their remarkable properties, challenges in synthesis and processing have hindered integration in current electronics. Challenges include the inability to precisely assemble and control the deposition of SWNT films on a variety of surfaces and the lack of understanding of the transport properties of these films. Here, we utilize an optimized "dry transfer" technique that facilitates the complete intact transfer of SWNT films between different surfaces. We then show the effect of surface chemistry on the electronic properties of SWNT films. By isolating the effect of the surface, we gain insight into the fundamental transport properties of SWNTs on surfaces with different chemical functionalities. Thin film transistor (TFT) characteristics, corroborated with μ-Raman spectroscopy, show that by using different surface chemical functionalities it is possible to alter the electronic properties of SWNT films. This opens up another route to tune the electronic properties of integrated SWNT films.

  View details for DOI 10.1021/nn1012226

  View details for Web of Science ID 000283453700085

  View details for PubMedID 20857943

• Driving High-Performance n- and p-type Organic Transistors with Carbon Nanotube/Conjugated Polymer Composite Electrodes Patterned Directly from Solution ADVANCED MATERIALS Hellstrom, S. L., Jin, R. Z., Stoltenberg, R. M., Bao, Z. 2010; 22 (37): 4204-?

  Abstract

  We report patterned deposition of carbon nanotube/conjugated polymer composites from solution with high nanotube densities and excellent feature resolution. Such composites are suited for use as electrodes in high-performance transistors of pentacene and C(60), with bottom-contact mobilities of > 0.5 and > 1 cm(2) V(−1) s(−1), respectively. This represents a clear step towards development of inexpensive, high-performance all-organic circuits.

  View details for DOI 10.1002/adma.201001435

  View details for Web of Science ID 000283392000017

  View details for PubMedID 20626010

• Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers NATURE MATERIALS Mannsfeld, S. C., Tee, B. C., Stoltenberg, R. M., Chen, C. V., Barman, S., Muir, B. V., Sokolov, A. N., Reese, C., Bao, Z. 2010; 9 (10): 859-864

  Abstract

  The development of an electronic skin is critical to the realization of artificial intelligence that comes into direct contact with humans, and to biomedical applications such as prosthetic skin. To mimic the tactile sensing properties of natural skin, large arrays of pixel pressure sensors on a flexible and stretchable substrate are required. We demonstrate flexible, capacitive pressure sensors with unprecedented sensitivity and very short response times that can be inexpensively fabricated over large areas by microstructuring of thin films of the biocompatible elastomer polydimethylsiloxane. The pressure sensitivity of the microstructured films far surpassed that exhibited by unstructured elastomeric films of similar thickness, and is tunable by using different microstructures. The microstructured films were integrated into organic field-effect transistors as the dielectric layer, forming a new type of active sensor device with similarly excellent sensitivity and response times.

  View details for DOI 10.1038/nmat2834

  View details for Web of Science ID 000282134700025

  View details for PubMedID 20835231

• Organic Semiconductor Growth and Morphology Considerations for Organic Thin-Film Transistors ADVANCED MATERIALS Virkar, A. A., Mannsfeld, S., Bao, Z., Stingelin, N. 2010; 22 (34): 3857-3875

  Abstract

  Analogous to conventional inorganic semiconductors, the performance of organic semiconductors is directly related to their molecular packing, crystallinity, growth mode, and purity. In order to achieve the best possible performance, it is critical to understand how organic semiconductors nucleate and grow. Clever use of surface and dielectric modification chemistry can allow one to control the growth and morphology, which greatly influence the electrical properties of the organic transistor. In this Review, the nucleation and growth of organic semiconductors on dielectric surfaces is addressed. The first part of the Review concentrates on small-molecule organic semiconductors. The role of deposition conditions on film formation is described. The modification of the dielectric interface using polymers or self-assembled mono-layers and their effect on organic-semiconductor growth and performance is also discussed. The goal of this Review is primarily to discuss the thin-film formation of organic semiconducting species. The patterning of single crystals is discussed, while their nucleation and growth has been described elsewhere (see the Review by Liu et. al).([¹]) The second part of the Review focuses on polymeric semiconductors. The dependence of physico-chemical properties, such as chain length (i.e., molecular weight) of the constituting macromolecule, and the influence of small molecular species on, e.g., melting temperature, as well as routes to induce order in such macromolecules, are described.

  View details for DOI 10.1002/adma.200903193

  View details for Web of Science ID 000282793600007

  View details for PubMedID 20715062

• Effects of Dispersion Conditions of Single-Walled Carbon Nanotubes on the Electrical Characteristics of Thin Film Network Transistors ACS APPLIED MATERIALS & INTERFACES Barman, S. N., LeMieux, M. C., Baek, J., Rivera, R., Bao, Z. 2010; 2 (9): 2672-2678

  Abstract

  To facilitate solution deposition of single-walled carbon nanotubes (SWNTs) for integration into electronic devices they need to be purified and dispersed into solutions. The vigorous sonication process for preparing these dispersions leads to large variations in the length and defect density of SWNTs, affecting the resulting electronic properties. Understanding the effects of solution processing steps can have important implications in the design of SWNT films for electronic applications. Here, we alter the SWNTs by varying the sonication time, followed by deposition of sub-monolayer SWNT network films onto functionalized substrates. The corresponding electrical performance characteristics of the resulting field effect transistors (FETs) are correlated with SWNT network sorting and morphology. As sonication exposure increases, the SWNTs shorten, which not only affects electrical current by increasing the number of junctions but also presumably leads to more defects. The off current of the resulting transistors initially increased with sonication exposure, presumably due to less efficient sorting of semiconducting SWNTs as the defect density increases. After extended sonication, the on and off current decreased because of increased bundling and fewer percolation pathways. The final transistor properties are influenced by the nanotube solution concentration, density, alignment, and the selectivity of surface sorting of the SWNT networks. These results show that in addition to chirality, careful consideration of SWNT dispersion conditions that affect SWNT length, bundle diameter, and defect density is critical for optimal SWNT-FET performance and potentially other SWNT-based electronic devices.

  View details for DOI 10.1021/am1005223

  View details for Web of Science ID 000282017700029

  View details for PubMedID 20738099

• Tuning the Optoelectronic Properties of Vinylene-Linked Donor-Acceptor Copolymers for Organic Photovoltaics MACROMOLECULES Ko, S., Mondal, R., Risko, C., Lee, J. K., Hong, S., McGehee, M. D., Bredas, J., Bao, Z. 2010; 43 (16): 6685-6698

  View details for DOI 10.1021/ma101088f

  View details for Web of Science ID 000280855000023

• Anthradithiophene-Containing Copolymers for Thin-Film Transistors and Photovoltaic Cells MACROMOLECULES Jiang, Y., Okamoto, T., Becerril, H. A., Hong, S., Tang, M. L., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2010; 43 (15): 6361-6367

  View details for DOI 10.1021/ma1001639

  View details for Web of Science ID 000280743300017

• Contact engineering for organic semiconductor devices via Fermi level depinning at the metal-organic interface PHYSICAL REVIEW B Liu, Z., Kobayashi, M., Paul, B. C., Bao, Z., Nishi, Y. 2010; 82 (3)

  View details for DOI 10.1103/PhysRevB.82.035311

  View details for Web of Science ID 000280123900004

• High-Performance Air-Stable n-Type Organic Transistors Based on Core-Chlorinated Naphthalene Tetracarboxylic Diimides ADVANCED FUNCTIONAL MATERIALS Oh, J. H., Suraru, S., Lee, W., Koenemann, M., Hoeffken, H. W., Roeger, C., Schmidt, R., Chung, Y., Chen, W., Wuerthner, F., Bao, Z. 2010; 20 (13): 2148-2156

  View details for DOI 10.1002/adfm.201000425

  View details for Web of Science ID 000280276900016

• Use of a 1H-Benzoimidazole Derivative as an n-Type Dopant and To Enable Air-Stable Solution-Processed n-Channel Organic Thin-Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wei, P., Oh, J. H., Dong, G., Bao, Z. 2010; 132 (26): 8852-?

  Abstract

  We present here the development of a new solution-processable n-type dopant, N-DMBI. Our experimental results demonstrated that a well-known n-channel semiconductor, [6,6]-phenyl C(61) butyric acid methyl ester (PCBM), can be effectively doped with N-DMBI by solution processing; the film conductivity is significantly increased by n-type doping. We utilized this n-type doping for the first time to improve the air-stability of n-channel organic thin-film transistors, in which the doping can compensate for the electron traps. Our successful demonstration of n-type doping using N-DMBI opens up new opportunities for the development of air-stable n-channel semiconductors. It is also potentially useful for application on solution-processed organic light-emitting diodes and organic photovoltaics.

  View details for DOI 10.1021/ja103173m

  View details for Web of Science ID 000279561200019

  View details for PubMedID 20552967

• X-ray Microscopy Imaging of the Grain Orientation in a Pentacene Field-Effect Transistor CHEMISTRY OF MATERIALS Braeuer, B., Virkar, A., Mannsfeld, S. C., Bernstein, D. P., Kukreja, R., Chou, K. W., Tyliszczak, T., Bao, Z., Acremann, Y. 2010; 22 (12): 3693-3697

  View details for DOI 10.1021/cm100487j

  View details for Web of Science ID 000278684000016

• Induced Sensitivity and Selectivity in Thin-Film Transistor Sensors via Calixarene Layers ADVANCED MATERIALS Sokolov, A. N., Roberts, M. E., Johnson, O. B., Cao, Y., Bao, Z. 2010; 22 (21): 2349-2353

  View details for DOI 10.1002/adma.200903305

  View details for Web of Science ID 000279100200010

  View details for PubMedID 20376848

• Nanotubes on Display: How Carbon Nanotubes Can Be Integrated into Electronic Displays ACS NANO Opatkiewicz, J., LeMieux, M. C., Bao, Z. 2010; 4 (6): 2975-2978

  Abstract

  Random networks of single-walled carbon nanotubes show promise for use in the field of flexible electronics. Nanotube networks have been difficult to utilize because of the mixture of electronic types synthesized when grown. A variety of separation techniques have been developed, but few can readily be scaled up. Despite this issue, when metallic percolation pathways can be separated out or etched away, these networks serve as high-quality thin-film transistors with impressive device characteristics. A new article in this issue illustrates this point and the promise of these materials. With more work, these devices can be implemented in transparent displays in the next generation of hand-held electronics.

  View details for DOI 10.1021/nn101092d

  View details for Web of Science ID 000278888600003

  View details for PubMedID 20565139

• Band structure measurement of organic single crystal with angle-resolved photoemission APPLIED PHYSICS LETTERS Ding, H., Reese, C., Maekinen, A. J., Bao, Z., Gao, Y. 2010; 96 (22)

  View details for DOI 10.1063/1.3446849

  View details for Web of Science ID 000278404800029

• Parallel Fabrication of Electrode Arrays on Single-Walled Carbon Nanotubes using Dip-Pen-Nanolithography-Patterned Etch Masks LANGMUIR Park, S., Wang, W. M., Bao, Z. 2010; 26 (9): 6853-6859

  Abstract

  This article presents a novel application of using dip-pen nanolithography (DPN) to fabricate Au electrodes concurrently in a high-throughput fashion through an etch resist. We have fabricated 26 pairs of electrodes, where cleanly etched electrode architectures, along with a high degree of feature-size controllability and tip-to-tip uniformity, were observed. Moreover, electrode gaps in the sub-100-nm regime have been successfully fabricated. Conductivity measurements of multiple electrodes in the array were all comparable to that of bulk Au, confirming the reliability and the low-resistance property of the electrodes. Finally, as a demonstration of electrode functionality, SWNT devices were fabricated and the electrical properties of an SWNT device were measured. Hence, our experimental results validate DPN as an effective tool in generating high-quality electrodes in a parallel manner with mild, simple processing steps at a relatively low cost.

  View details for DOI 10.1021/la904170w

  View details for Web of Science ID 000276969700114

  View details for PubMedID 20163131

• Biomaterials-based organic electronic devices POLYMER INTERNATIONAL Bettinger, C. J., Bao, Z. 2010; 59 (5): 563-567

  Abstract

  Organic electronic devices have demonstrated tremendous versatility in a wide range of applications including consumer electronics, photovoltaics, and biotechnology. The traditional interface of organic electronics with biology, biotechnology, and medicine occurs in the general field of sensing biological phenomena. For example, the fabrication of hybrid electronic structures using both organic semiconductors and bioactive molecules has led to enhancements in sensitivity and specificity within biosensing platforms, which in turn has a potentially wide range of clinical applications. However, the interface of biomolecules and organic semiconductors has also recently explored the potential use of natural and synthetic biomaterials as structural components of electronic devices. The fabrication of electronically active systems using biomaterials-based components has the potential to realize a large set of unique devices including environmentally biodegradable systems and bioresorbable temporary medical devices. This article reviews recent advances in the implementation of biomaterials as structural components in organic electronic devices with a focus on potential applications in biotechnology and medicine.

  View details for DOI 10.1002/pi.2827

  View details for Web of Science ID 000277767500001

  View details for PubMedCentralID PMC2895275

• Biomaterials-Based Organic Electronic Devices. Polymer international Bettinger, C. J., Bao, Z. 2010; 59 (5): 563-567

  Abstract

  Organic electronic devices have demonstrated tremendous versatility in a wide range of applications including consumer electronics, photovoltaics, and biotechnology. The traditional interface of organic electronics with biology, biotechnology, and medicine occurs in the general field of sensing biological phenomena. For example, the fabrication of hybrid electronic structures using both organic semiconductors and bioactive molecules has led to enhancements in sensitivity and specificity within biosensing platforms, which in turn has a potentially wide range of clinical applications. However, the interface of biomolecules and organic semiconductors has also recently explored the potential use of natural and synthetic biomaterials as structural components of electronic devices. The fabrication of electronically active systems using biomaterials-based components has the potential to realize a large set of unique devices including environmentally biodegradable systems and bioresorbable temporary medical devices. This article reviews recent advances in the implementation of biomaterials as structural components in organic electronic devices with a focus on potential applications in biotechnology and medicine.

  View details for DOI 10.1002/pi.2827

  View details for PubMedID 20607127

  View details for PubMedCentralID PMC2895275

• Low-voltage and short-channel pentacene field-effect transistors with top-contact geometry using parylene-C shadow masks APPLIED PHYSICS LETTERS Chung, Y., Murmann, B., Selvarasah, S., Dokmeci, M. R., Bao, Z. 2010; 96 (13)

  View details for DOI 10.1063/1.3336009

  View details for Web of Science ID 000276275300063

• Influence of Electrostatic Interactions on Spin-Assembled Single-Walled Carbon Nanotube Networks on Amine-Functionalized Surfaces ACS NANO Opatkiewicz, J. P., LeMieux, M. C., Bao, Z. 2010; 4 (2): 1167-1177

  Abstract

  Preferential interactions between self-assembled monolayers (SAMs) terminated with amine functional groups and single-walled carbon nanotubes (SWNTs) were exploited to produce nanotube networks (SWNTnts) via spin coating. We provide insight into the mechanisms of this system while simultaneously demonstrating a facile approach toward controllable arrays of SWNTnts. The chirality, density, and alignment of the SWNTnt was heavily influenced by adsorption onto amine-functionalized surfaces that were exposed to varying pH solutions, as evidenced by atomic force microscopy (AFM) and Raman spectroscopy. This pH treatment altered the charge density on the surface, allowing for the examination of the contribution from electrostatic interaction to SWNT adsorption and SWNTnt characteristics. Secondary and tertiary amines with methyl substitutions were utilized to confirm that adsorption and chirality specific adsorption is largely due to the nitrogen lone pair, not the neighboring hydrogen atoms. Thus, the nature of adsorption is predominantly electrostatic and not due to van der Waals forces or localized polarization on the SWNTs. Moreover, the overall density of SWNTnts is different for the various amines, indicating that the accessibility to the lone pair electrons on the nitrogen plays a crucial role in SWNT adsorption. With greater understanding of the amine-SWNT interaction, these findings can be utilized to control SWNTnt formation for the precise integration into electronic devices.

  View details for DOI 10.1021/nn901388v

  View details for Web of Science ID 000274635800073

  View details for PubMedID 20112967

• Energetics and stability of pentacene thin films on amorphous and crystalline octadecylsilane modified surfaces JOURNAL OF MATERIALS CHEMISTRY Virkar, A. A., Mannsfeld, S. C., Bao, Z. 2010; 20 (13): 2664-2671

  View details for DOI 10.1039/b921767c

  View details for Web of Science ID 000275662400018

• Organic Thin-Film Transistors Fabricated on Resorbable Biomaterial Substrates Adv. Mater. Bettinger, C., Bao, Z. 2010; 22: 651-655
• A Crystal-Engineered Hydrogen-Bonded Octachloroperylene Diimide with a Twisted Core: An n-Channel Organic Semiconductor ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Gsaenger, M., Oh, J. H., Koenemann, M., Hoeffken, H. W., Krause, A., Bao, Z., Wuerthner, F. 2010; 49 (4): 740-743

  View details for DOI 10.1002/anie.200904215

  View details for Web of Science ID 000274424000012

• Organic Light-Emitting Diodes on Solution-Processed Graphene Transparent Electrodes ACS NANO Wu, J., Agrawal, M., Becerril, H. A., Bao, Z., Liu, Z., Chen, Y., Peumans, P. 2010; 4 (1): 43-48

  Abstract

  Theoretical estimates indicate that graphene thin films can be used as transparent electrodes for thin-film devices such as solar cells and organic light-emitting diodes, with an unmatched combination of sheet resistance and transparency. We demonstrate organic light-emitting diodes with solution-processed graphene thin film transparent conductive anodes. The graphene electrodes were deposited on quartz substrates by spin-coating of an aqueous dispersion of functionalized graphene, followed by a vacuum anneal step to reduce the sheet resistance. Small molecular weight organic materials and a metal cathode were directly deposited on the graphene anodes, resulting in devices with a performance comparable to control devices on indium-tin-oxide transparent anodes. The outcoupling efficiency of devices on graphene and indium-tin-oxide is nearly identical, in agreement with model predictions.

  View details for DOI 10.1021/nn900728d

  View details for Web of Science ID 000273863400007

  View details for PubMedID 19902961

• Thiophene-rich fused-aromatic thienopyrazine acceptor for donor-acceptor low band-gap polymers for OTFT and polymer solar cell applications JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Becerril, H. A., Verploegen, E., Kim, D., Norton, J. E., Ko, S., Miyaki, N., Lee, S., Toney, M. F., Bredas, J., McGehee, M. D., Bao, Z. 2010; 20 (28): 5823-5834

  View details for DOI 10.1039/c0jm00903b

  View details for Web of Science ID 000279565900008

• Fused aromatic thienopyrazines: structure, properties and function JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Bao, Z. 2010; 20 (47): 10568-10576

  View details for DOI 10.1039/c0jm01840f

  View details for Web of Science ID 000284542600001

• Solution Assembly of Organized Carbon Nanotube Networks for Thin-Film Transistors ACS NANO LeMieux, M. C., Sok, S., Roberts, M. E., Opatkiewicz, J. P., Liu, D., Barman, S. N., Patil, N., Mitra, S., Bao, Z. 2009; 3 (12): 4089-4097

  Abstract

  Ultrathin, transparent electronic materials consisting of solution-assembled nanomaterials that are directly integrated as thin-film transistors or conductive sheets may enable many new device structures. Applications ranging from disposable autonomous sensors to flexible, large-area displays and solar cells can dramatically expand the electronics market. With a practical, reliable method for controlling their electronic properties through solution assembly, submonolayer films of aligned single-walled carbon nanotubes (SWNTs) may provide a promising alternative for large-area, flexible electronics. Here, we report SWNT network TFTs (SWNTntTFTs) deposited from solution with controllable topology, on/off ratios averaging greater than 10(5), and an apparent mobility averaging 2 cm(2)/V.s, without any pre- or postprocessing steps. We employ a spin-assembly technique that results in chirality enrichment along with tunable alignment and density of the SWNTs by balancing the hydrodynamic force (spin rate) with the surface interaction force controlled by a chemically functionalized interface. This directed nanoscale assembly results in enriched semiconducting nanotubes yielding excellent TFT characteristics, which is corroborated with mu-Raman spectroscopy. Importantly, insight into the electronic properties of these SWNT networks as a function of topology is obtained.

  View details for DOI 10.1021/nn900827v

  View details for Web of Science ID 000272846000043

  View details for PubMedID 19924882

• Interplay between Energetic and Kinetic Factors on the Ambient Stability of n-Channel Organic Transistors Based on Perylene Diimide Derivatives CHEMISTRY OF MATERIALS Oh, J. H., Sun, Y., Schmidt, R., Toney, M. F., Nordlund, D., Koenemann, M., Wuerthner, F., Bao, Z. 2009; 21 (22): 5508-5518

  View details for DOI 10.1021/cm902531d

  View details for Web of Science ID 000271756400019

• Micrometer-Sized DNA-Single-Fluorophore-DNA Supramolecule: Synthesis and Single-Molecule Characterization SMALL Lee, J. K., Jaeckel, F., Moerner, W. E., Bao, Z. 2009; 5 (21): 2418-2423

  Abstract

  The synthesis of single-fluorophore-bis(micrometer-sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single-molecule level is reported. A fluorophore-bis(oligodeoxynucleotide) triblock is synthesized via the amide-coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with lambda-DNA fragments on the micrometer length scale. The successful synthesis of the micrometer-sized DNA-single-fluorophore-DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single-molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single-molecule electronic devices after metallization of the DNAs.

  View details for DOI 10.1002/smll.200900494

  View details for Web of Science ID 000271791100011

  View details for PubMedID 19517486

• Dip-Pen Nanolithography of Electrical Contacts to Single-Walled Carbon Nanotubes ACS NANO Wang, W. M., LeMieux, M. C., Selvarasah, S., Dokmeci, M. R., Bao, Z. 2009; 3 (11): 3543-3551

  Abstract

  This paper discusses a method for the direct patterning of Au electrodes at nanoscale resolution using dip-pen nanolithography, with proof-of-concept demonstrated by creating single-walled carbon nanotube devices. This technique enables insight into three key concepts at the nanoscale: using dip-pen nanolithography as an alternative to electron-beam lithography for writing contacts to carbon nanotubes, understanding the integrity of contacts and devices patterned with this technique, and on a more fundamental level, providing a facile method to compare and understand electrical and Raman spectroscopy data from the same isolated carbon nanotube. Electrical contacts to individual and small bundle single-walled carbon nanotubes were masked by an alkylthiol that was deposited via dip-pen nanolithography on a thin film of Au evaporated onto spin-cast, nonpercolating, and highly isolated single-walled carbon nanotubes. A wet Au etching step was used to form the individual devices. The electrical characteristics for three different single-walled carbon nanotube devices are reported: semimetallic, semiconducting, and metallic. Raman analysis on representative devices corroborates the results from AFM imaging and electrical testing. This work demonstrates a technique for making electrical contact to nanostructures of interest and provides a platform for directly corroborating electrical and optical measurements. The merits of using dip-pen nanolithography include flexible device configuration (such as varying the channel length and the number, size, and orientation of contacts), targeted patterning of individual devices with imaging and writing conducted in the same instrument under ambient conditions, and negligible damage to single-walled carbon nanotubes during the fabrication process.

  View details for DOI 10.1021/nn900984w

  View details for Web of Science ID 000271951200029

  View details for PubMedID 19852486

• Sorted and Aligned Single-Walled Carbon Nanotube Networks for Transistor-Based Aqueous Chemical Sensors ACS NANO Roberts, M. E., LeMieux, M. C., Bao, Z. 2009; 3 (10): 3287-3293

  Abstract

  Detecting trace amounts of analytes in aqueous systems is important for health diagnostics, environmental monitoring, and national security applications. Single-walled carbon nanotubes (SWNTs) are ideal components for both the sensor material and active signal transduction layer because of their excellent electronic properties and high aspect ratio consisting of entirely surface atoms. Submonolayer arrays, or networks of SWNTs (SWNTnts) are advantageous, and we show that topology characteristics of the SWNT network, such as alignment, degree of bundling, and chirality enrichment strongly affect the sensor performance. To enable this, thin-film transistor (TFT) sensors with SWNTnts were deposited using a one-step, low-cost, solution- based method on a polymer dielectric, allowing us to achieve stable low-voltage operation under aqueous conditions. These SWNT-TFTs were used to detect trace concentrations, down to 2 ppb, of dimethyl methylphosphonate (DMMP) and trinitrotoluene (TNT) in aqueous solutions. Along with reliable cycling underwater, the TFT sensors fabricated with aligned, sorted nanotube networks (enriched with semiconductor SWNTs) showed a higher sensitivity to analytes than those fabricated with random, unsorted networks with predominantly metallic charge transport.

  View details for DOI 10.1021/nn900808b

  View details for Web of Science ID 000271106100055

  View details for PubMedID 19856982

• Tuning Crystalline Solid-State Order and Charge Transport via Building-Block Modification of Oligothiophenes ADVANCED MATERIALS Reese, C., Roberts, M. E., Parkin, S. R., Bao, Z. 2009; 21 (36): 3678-?

  View details for DOI 10.1002/adma.200900836

  View details for Web of Science ID 000270441700010

• Fabrication of low-cost electronic biosensors MATERIALS TODAY Sokolov, A. N., Roberts, M. E., Bao, Z. 2009; 12 (9): 12-20

  View details for Web of Science ID 000270568800011

• Low-voltage transistor sensors based on organic semiconductors and carbon nanotube networks Roberts, M. E., LeMieux, M. C., Mannsfeld, S. C., Bao, Z. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207861905501

• Synthesis of Acenaphthyl and Phenanthrene Based Fused-Aromatic Thienopyrazine Co-Polymers for Photovoltaic and Thin Film Transistor Applications CHEMISTRY OF MATERIALS Mondal, R., Miyaki, N., Becerril, H. A., Norton, J. E., Parmer, J., Mayer, A. C., Tang, M. L., Bredas, J., McGehee, M. D., Bao, Z. 2009; 21 (15): 3618-3628

  View details for DOI 10.1021/cm900788e

  View details for Web of Science ID 000268523300021

• Crystalline Ultrasmooth Self-Assembled Monolayers of Alkylsilanes for Organic Field-Effect Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ito, Y., Virkar, A. A., Mannsfeld, S., Oh, J. H., Toney, M., Locklin, J., Bao, Z. 2009; 131 (26): 9396-9404

  Abstract

  Crystalline self-assembled monolayers (SAMs) of organosilane compounds such as octadecyltrimethoxysilane (OTMS) and octadecyltrichlorosilane (OTCS) were deposited by a simple, spin-casting technique onto Si/SiO(2) substrates. Fabrication of the OTMS SAMs and characterization using ellipsometry, contact angle, atomic force microscopy (AFM), grazing angle attenuated total reflectance Fourier transform infrared (GATR-FTIR) spectroscopy and grazing incidence X-ray diffraction (GIXD) are described. The characterization confirms that these monolayers exhibit a well-packed crystalline phase and a remarkably high degree of smoothness. Semiconductors deposited by vapor deposition onto the crystalline OTS SAM grow in a favorable two-dimensional layered growth manner which is generally preferred morphologically for high charge carrier transport. On the OTMS SAM treated dielectric, pentacene OFETs showed hole mobilities as high as 3.0 cm(2)/V x s, while electron mobilities as high as 5.3 cm(2)/V x s were demonstrated for C(60).

  View details for DOI 10.1021/ja9029957

  View details for Web of Science ID 000267633300056

  View details for PubMedID 19518097

• Self-Sorted Nanotube Networks on Polymer Dielectrics for Low-Voltage Thin-Film Transistors NANO LETTERS Roberts, M. E., LeMieux, M. C., Sokolov, A. N., Bao, Z. 2009; 9 (7): 2526-2531

  Abstract

  Recent exploitations of the superior mechanical and electronic properties of carbon nanotubes (CNTs) have led to exciting opportunities in low-cost, high performance, carbon-based electronics. In this report, low-voltage thin-film transistors with aligned, semiconducting CNT networks are fabricated on a chemically modified polymer gate dielectric using both rigid and flexible substrates. The multifunctional polymer serves as a thin, flexible gate dielectric film, affords low operating voltages, and provides a platform for chemical functionalization. The introduction of amine functionality to the dielectric surface leads to the adsorption of a network enriched with semiconducting CNTs with tunable density from spin coating a bulk solution of unsorted CNTs. The composition of the deposited CNT networks is verified with Raman spectroscopy and electrical characterization. For transistors at operating biases below 1 V, we observe an effective device mobility as high as 13.4 cm(2)/Vs, a subthreshold swing as low as 130 mV/dec, and typical on-off ratios of greater than 1,000. This demonstration of high performance CNT thin-film transistors operating at voltages below 1 V and deposited using solution methods on polymeric and flexible substrates is an important step toward the realization of low-cost flexible electronics.

  View details for DOI 10.1021/nl900287p

  View details for Web of Science ID 000268138600003

  View details for PubMedID 19499894

• The Role of OTS Density on Pentacene and C-60 Nucleation, Thin Film Growth, and Transistor Performance ADVANCED FUNCTIONAL MATERIALS Virkar, A., Mannsfeld, S., Oh, J. H., Toney, M. F., Tan, Y. H., Liu, G., Scott, J. C., Miller, R., Bao, Z. 2009; 19 (12): 1962-1970

  View details for DOI 10.1002/adfm.200801727

  View details for Web of Science ID 000267509900015

• Precise Structure of Pentacene Monolayers on Amorphous Silicon Oxide and Relation to Charge Transport ADVANCED MATERIALS Mannsfeld, S. C., Virkar, A., Reese, C., Toney, M. F., Bao, Z. 2009; 21 (22): 2294-?

  View details for DOI 10.1002/adma.200803328

  View details for Web of Science ID 000267509500006

• Cross-Linked Polymer Gate Dielectric Films for Low-Voltage Organic Transistors CHEMISTRY OF MATERIALS Roberts, M. E., Queralto, N., Mannsfeld, S. C., Reinecke, B. N., Knoll, W., Bao, Z. 2009; 21 (11): 2292-2299

  View details for DOI 10.1021/cm900637p

  View details for Web of Science ID 000266708700017

• Polymer-Assisted Direct Deposition of Uniform Carbon Nanotube Bundle Networks for High Performance Transparent Electrodes ACS NANO Hellstrom, S. L., Lee, H. W., Bao, Z. 2009; 3 (6): 1423-1430

  Abstract

  Flexible transparent electrodes are crucial for touch screen, flat panel display, and solar cell technologies. While carbon nanotube network electrodes show promise, characteristically poor dispersion properties have limited their practicality. We report that addition of small amounts of conjugated polymer to nanotube dispersions enables straightforward fabrication of uniform network electrodes by spin-coating and simultaneous tuning of parameters such as bundle size and density. After treatment in thionyl chloride, electrodes have sheet resistances competitive with other reported carbon nanotube based transparent electrodes to date.

  View details for DOI 10.1021/nn9002456

  View details for Web of Science ID 000267533600016

  View details for PubMedID 19422197

• Isotropic transport in an oligothiophene derivative for single-crystal field-effect transistor applications APPLIED PHYSICS LETTERS Reese, C., Roberts, M. E., Parkin, S. R., Bao, Z. 2009; 94 (20)

  View details for DOI 10.1063/1.3129162

  View details for Web of Science ID 000266342800026

• Solution-processed flexible organic transistors showing very-low subthreshold slope with a bilayer polymeric dielectric on plastic APPLIED PHYSICS LETTERS Liu, Z., Oh, J. H., Roberts, M. E., Wei, P., Paul, B. C., Okajima, M., Nishi, Y., Bao, Z. 2009; 94 (20)

  View details for DOI 10.1063/1.3133902

  View details for Web of Science ID 000266342800065

• Liquid-Crystalline Semiconducting Copolymers with Intramolecular Donor-Acceptor Building Blocks for High-Stability Polymer Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kim, D. H., Lee, B., Moon, H., Kang, H. M., Jeong, E. J., Park, J., Han, K., Lee, S., Yoo, B. W., Koo, B. W., Kim, J. Y., Lee, W. H., Cho, K., Becerril, H. A., Bao, Z. 2009; 131 (17): 6124-6132

  Abstract

  The ability to control the molecular organization of electronically active liquid-crystalline polymer semiconductors on surfaces provides opportunities to develop easy-to-process yet highly ordered supramolecular systems and, in particular, to optimize their electrical and environmental reliability in applications in the field of large-area printed electronics and photovoltaics. Understanding the relationship between liquid-crystalline nanostructure and electrical stability on appropriate molecular surfaces is the key to enhancing the performance of organic field-effect transistors (OFETs) to a degree comparable to that of amorphous silicon (a-Si). Here, we report a novel donor-acceptor type liquid-crystalline semiconducting copolymer, poly(didodecylquaterthiophene-alt-didodecylbithiazole), which contains both electron-donating quaterthiophene and electron-accepting 5,5'-bithiazole units. This copolymer exhibits excellent electrical characteristics such as field-effect mobilities as high as 0.33 cm(2)/V.s and good bias-stress stability comparable to that of amorphous silicon (a-Si). Liquid-crystalline thin films with structural anisotropy form spontaneously through self-organization of individual polymer chains as a result of intermolecular interactions in the liquid-crystalline mesophase. These thin films adopt preferential well-ordered intermolecular pi-pi stacking parallel to the substrate surface. This bottom-up assembly of the liquid-crystalline semiconducting copolymer enables facile fabrication of highly ordered channel layers with remarkable electrical stability.

  View details for DOI 10.1021/ja8095569

  View details for Web of Science ID 000265755800036

  View details for PubMedID 19354240

• High-Performance Air-Stable n-Channel Organic Thin Film Transistors Based on Halogenated Perylene Bisimide Semiconductors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Schmidt, R., Oh, J. H., Sun, Y., Deppisch, M., Krause, A., Radacki, K., Braunschweig, H., Koenemann, M., Erk, P., Bao, Z., Wuerthner, F. 2009; 131 (17): 6215-6228

  Abstract

  The syntheses and comprehensive characterization of 14 organic semiconductors based on perylene bisimide (PBI) dyes that are equipped with up to four halogen substituents in the bay area of the perylene core and five different highly fluorinated imide substituents are described. The influence of the substituents on the LUMO level and the solid state packing of PBIs was examined by cyclic voltammetry and single crystal structure analyses of seven PBI derivatives, respectively. Top-contact/bottom-gate organic thin film transistor (OTFT) devices were constructed by vacuum deposition of these PBIs on SiO(2) gate dielectrics that had been pretreated with n-octadecyl triethoxysilane in vapor phase (OTS-V) or solution phase (OTS-S). The electrical characterization of all devices was accomplished in a nitrogen atmosphere as well as in air, and the structural features of thin films were explored by grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM). Several of those PBIs that bear only hydrogen or up to two fluorine substitutents at the concomitantly flat PBI core afforded excellent n-channel transistors, in particular, on OTS-S substrate and even in air (mu > 0.5 cm(2) V(-1) s(-1); I(on)/I(off) > 10(6)). The best OTFTs were obtained for 2,2,3,3,4,4,4-heptafluorobutyl-substituted PBI 1a ("PTCDI-C4F7") on OTS-S with n-channel field effect mobilities consistently >1 cm(2) V(-1) s(-1) and on-to-off current rations of 10(6) in a nitrogen atmosphere and in air. For distorted core-tetrahalogenated (fluorine, chlorine, or bromine) PBIs, less advantageous solid state packing properties were found and high performance OTFTs were obtained from only one tetrachlorinated derivative (2d on OTS-S). The excellent on-to-off current modulation combined with high mobility in air makes these PBIs suitable for a wide range of practical applications.

  View details for DOI 10.1021/ja901077a

  View details for Web of Science ID 000265755800047

  View details for PubMedID 19354212

• Lyotropic Liquid-Crystalline Solutions of High-Concentration Dispersions of Single-Walled Carbon Nanotubes with Conjugated Polymers SMALL Lee, H. W., You, W., Barman, S., Hellstrom, S., LeMieux, M. C., Oh, J. H., Liu, S., Fujiwara, T., Wang, W. M., Chen, B., Jin, Y. W., Kim, J. M., Bao, Z. 2009; 5 (9): 1019-1024

  View details for DOI 10.1002/smll.200800640

  View details for Web of Science ID 000266184500004

  View details for PubMedID 19291730

• Flexible, plastic transistor-based chemical sensors ORGANIC ELECTRONICS Roberts, M. E., Mannsfeld, S. C., Stoltenberg, R. M., Bao, Z. 2009; 10 (3): 377-383

  View details for DOI 10.1016/j.orgel.2008.12.001

  View details for Web of Science ID 000266000700001

• Correlating Carrier Type with Frontier Molecular Orbital Energy Levels in Organic Thin Film Transistors of Functionalized Acene Derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Reichardt, A. D., Wei, P., Bao, Z. 2009; 131 (14): 5264-5273

  Abstract

  We investigate the relationship between the charge carrier type in organic thin film transistors (OTFTs) and molecular energy levels. We examine a series of functionalized acenes that collectively have their HOMOs range from -4.9 eV to -5.6 eV and LUMOs range from -2.8 eV to -3.7 eV, as measured by cyclic voltammetry. Placed together, these 20 molecules allow us to chart the transition from OTFTs that display only hole transport, to ambipolar, to solely electron transport. Specifically, we note that for octadecyltrimethoxysilane (OTS) treated substrates, with top contact gold electrodes, electron injection and transport occurs when the LUMO < -3.15 eV, while hole injection and transport ceases when the HOMO < -5.6 eV. Ambipolar transport prevails when molecules have HOMO/ LUMO levels within the aforementioned range. This is seen across channel lengths ranging from 50-150 microm and using only gold as electrodes. This empirical plot is the first time such a detailed study has been made on the onset of charge injection and transport for a class of organic semiconductors. It provides guidelines for future molecular design.

  View details for DOI 10.1021/ja809659b

  View details for Web of Science ID 000265039000053

  View details for PubMedID 19317404

• Solution-processed, high-performance n-channel organic microwire transistors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Oh, J. H., Lee, H. W., Mannsfeld, S., Stoltenberg, R. M., Jung, E., Jin, Y. W., Kim, J. M., Yoo, J., Bao, Z. 2009; 106 (15): 6065-6070

  Abstract

  The development of solution-processable, high-performance n-channel organic semiconductors is crucial to realizing low-cost, all-organic complementary circuits. Single-crystalline organic semiconductor nano/microwires (NWs/MWs) have great potential as active materials in solution-formed high-performance transistors. However, the technology to integrate these elements into functional networks with controlled alignment and density lags far behind their inorganic counterparts. Here, we report a solution-processing approach to achieve high-performance air-stable n-channel organic transistors (the field-effect mobility (mu) up to 0.24 cm(2)/Vs for MW networks) comprising high mobility, solution-synthesized single-crystalline organic semiconducting MWs (mu as high as 1.4 cm(2)/Vs for individual MWs) and a filtration-and-transfer (FAT) alignment method. The FAT method enables facile control over both alignment and density of MWs. Our approach presents a route toward solution-processed, high-performance organic transistors and could be used for directed assembly of various functional organic and inorganic NWs/MWs.

  View details for DOI 10.1073/pnas.0811923106

  View details for Web of Science ID 000265174600009

  View details for PubMedID 19299506

  View details for PubMedCentralID PMC2669358

• Direct Patterning of Organic-Thin-Film-Transistor Arrays via a "Dry-Taping" Approach ADVANCED MATERIALS Liu, S., Becerril, H. A., LeMieux, M. C., Wang, W. M., Oh, J. H., Bao, Z. 2009; 21 (12): 1266-?

  View details for DOI 10.1002/adma.200802201

  View details for Web of Science ID 000264926800009

• Controlled Deposition of Crystalline Organic Semiconductors for Field-Effect-Transistor Applications ADVANCED MATERIALS Liu, S., Wang, W. M., Briseno, A. L., Mannsfeld, S. C., Bao, Z. 2009; 21 (12): 1217-1232

  View details for DOI 10.1002/adma.200802202

  View details for Web of Science ID 000264926800001

• Chlorination: A General Route toward Electron Transport in Organic Semiconductors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Oh, J. H., Reichardt, A. D., Bao, Z. 2009; 131 (10): 3733-3740

  Abstract

  We show that adding chlorine atoms to conjugated cores is a general, effective route toward the design of n-type air-stable organic semiconductors. We find this to be true for acenes, phthalocyanines, and perylene tetracarboxylic diimide (PDI)-based molecules. This general finding opens new avenues in the design and synthesis of organic semiconductors. We compared a series of fluoro- and chloro-functionalized acenes, phthalocyanines, and PDI-based molecules. The acenes synthesized showed high and balanced ambipolar transport in the top-contact organic field effect transistor (OFET) geometry. The electron-withdrawing halogen groups lowered the LUMO and the charge injection barrier for electrons, such that electron and hole transport occurred simultaneously. If the chlorine added does not distort the planarity of the conjugated core, we found that the chloro-functionalized molecules tend to have a slightly smaller HOMO-LUMO gap and a lower LUMO level than the fluoro-containing molecules, both from calculations and cyclic voltammetry measurements in solution. This is most likely due to the fact that Cl contains empty 3d orbitals that can accept pi-electrons from the conjugated core, while F does not have energetically accessible empty orbitals for such delocalization.

  View details for DOI 10.1021/ja809045s

  View details for Web of Science ID 000264792600065

  View details for PubMedID 19243143

• Detailed Characterization of Contact Resistance, Gate-Bias-Dependent Field-Effect Mobility, and Short-Channel Effects with Microscale Elastomeric Single-Crystal Field-Effect Transistors ADVANCED FUNCTIONAL MATERIALS Reese, C., Bao, Z. 2009; 19 (5): 763-771

  View details for DOI 10.1002/adfm.200801019

  View details for Web of Science ID 000264502000012

• Experimental Study and Statistical Analysis of Solution-Shearing Processed Organic Transistors Based on an Asymmetric Small-Molecule Semiconductor IEEE TRANSACTIONS ON ELECTRON DEVICES Liu, Z., Becerril, H. A., Roberts, M. E., Nishi, Y., Bao, Z. 2009; 56 (2): 176-185

  View details for DOI 10.1109/TED.2008.2010580

  View details for Web of Science ID 000262816800004

• Pentaceno[2,3-b]thiophene, a Hexacene Analogue for Organic Thin Film Transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Mannsfeld, S. C., Sun, Y., Becerril, H. A., Bao, Z. 2009; 131 (3): 882-?

  Abstract

  Hexacene and larger fused rings remain elusive targets for chemists. Here, we report a hexacene-like molecule containing six linearly fused rings, specifically a pentacene molecule fused with a terminal thiophene ring, pentaceno[2,3-b]thiophene. It can be purified and isolated as a purple-black powder at ambient conditions. This molecule has a low HOMO-LUMO gap of 1.75 eV in o-DCB and an optical band gap of 1.58 eV in thin film. Top contact organic thin film transistors (OTFTs) were made, and atomic force microscopy (AFM) reveals a dendritic thin film growth characteristic of pentacene. An OTFT mobility of 0.574 cm(2)/V s was measured for pentaceno[2,3-b]thiophene under nitrogen.

  View details for DOI 10.1021/ja808142c

  View details for Web of Science ID 000264791600005

  View details for PubMedID 19125619

• Overestimation of the field-effect mobility via transconductance measurements and the origin of the output/transfer characteristic discrepancy in organic field-effect transistors JOURNAL OF APPLIED PHYSICS Reese, C., Bao, Z. 2009; 105 (2)

  View details for DOI 10.1063/1.3029587

  View details for Web of Science ID 000262970900112

• Patterning of alpha-Sexithiophene Single Crystals with Precisely Controlled Sizes and Shapes CHEMISTRY OF MATERIALS Liu, S., Mannsfeld, S. C., Wang, W. M., Sun, Y., Stoltenberg, R. M., Bao, Z. 2009; 21 (1): 15-17

  View details for DOI 10.1021/cm802806t

  View details for Web of Science ID 000262266500006

• Transistor and solar cell performance of donor-acceptor low bandgap copolymers bearing an acenaphtho[1,2-b]thieno[3,4-e]pyrazine (ACTP) motif JOURNAL OF MATERIALS CHEMISTRY Becerril, H. A., Miyaki, N., Tang, M. L., Mondal, R., Sun, Y., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2009; 19 (5): 591-593

  View details for DOI 10.1039/b819210c

  View details for Web of Science ID 000262547000003

• Solution-processed, high-performance n-channel organic nanowire transistors Proc. Nat. Acad. Sci. USA Oh, J., H., Lee, H., W., Mannsfeld, S., C.B., Stoltenberg, R., M., Jung, E., Jin, Y., W., Bao, Z. 2009; 106: 6065-6070
• Chlorination: a general route towards electron transport in organic semiconductors J. Am. Chem. Soc. Tang, M., L., Oh, J., H., Reichardt, A., D., Bao, Z. 2009; 131: 3733-3740
• Solution Assembly of Transistor Arrays Based on Sorted Nanotube Networks for Large-scale Flexible Electronic Applications 47th Annual Symposium of the Society-for-Information-Display LeMieux, M. C., Roberts, M., Opatkiewicz, J., Bao, Z., Patil, N., Mitra, S. SOC INFORMATION DISPLAY. 2009: 877–879

  View details for Web of Science ID 000272997600227

• Molecular design for improved photovoltaic efficiency: band gap and absorption coefficient engineering JOURNAL OF MATERIALS CHEMISTRY Mondal, R., Ko, S., Norton, J. E., Miyaki, N., Becerril, H. A., Verploegen, E., Toney, M. F., Bredas, J., McGehee, M. D., Bao, Z. 2009; 19 (39): 7195-7197

  View details for DOI 10.1039/b915222a

  View details for Web of Science ID 000270382400004

• Material and device considerations for organic thin-film transistor sensors JOURNAL OF MATERIALS CHEMISTRY Roberts, M. E., Sokolov, A. N., Bao, Z. 2009; 19 (21): 3351-3363

  View details for DOI 10.1039/b816386c

  View details for Web of Science ID 000266269300003

• New indolo[3,2-b]carbazole derivatives for field-effect transistor applications JOURNAL OF MATERIALS CHEMISTRY Boudreault, P. T., Wakim, S., Tang, M. L., Tao, Y., Bao, Z., Leclerc, M. 2009; 19 (19): 2921-2928

  View details for DOI 10.1039/b900271e

  View details for Web of Science ID 000265919300008

• Influence of Molecular Structure And Film Properties on the Water-Stability and Sensor Characteristics of Organic Transistors CHEMISTRY OF MATERIALS Roberts, M. E., Mannsfeld, S. C., Tang, M. L., Bao, Z. 2008; 20 (23): 7332-7338

  View details for DOI 10.1021/cm802530x

  View details for Web of Science ID 000261335200021

• Oligothiophene based organic semiconductors with cross-linkable benzophenone moieties SYNTHETIC METALS Virkar, A., Ling, M., Locklin, J., Bao, Z. 2008; 158 (21-24): 958-963

  View details for DOI 10.1016/j.synthmet.2008.06.019

  View details for Web of Science ID 000262573900030

• Highly Efficient Patterning of Organic Single-Crystal Transistors from the Solution Phase ADVANCED MATERIALS Mannsfeld, S. C., Sharei, A., Liu, S., Roberts, M. E., McCulloch, I., Heeney, M., Bao, Z. 2008; 20 (21): 4044-?

  View details for DOI 10.1002/adma.200703244

  View details for Web of Science ID 000261040000007

• Synthesis and characterization of pentacene- and anthradithiophene-fluorene conjugated copolymers synthesized by Suzuki reactions MACROMOLECULES Okamoto, T., Jiang, Y., Qu, F., Mayer, A. C., Parmer, J. E., McGehee, M. D., Bao, Z. 2008; 41 (19): 6977-6980

  View details for DOI 10.1021/ma800931a

  View details for Web of Science ID 000259859800020

• FLEXIBLE ELECTRONICS Stretching our imagination NATURE NANOTECHNOLOGY LeMieux, M. C., Bao, Z. 2008; 3 (10): 585-586

  View details for DOI 10.1038/nnano.2008.296

  View details for Web of Science ID 000260314300006

  View details for PubMedID 18838993

• Direct Patterning of Gold Nanoparticles Using Dip-Pen Nanolithography ACS NANO Wang, W. M., Stoltenberg, R. M., Liu, S., Bao, Z. 2008; 2 (10): 2135-2142

  Abstract

  Various methods for the patterned assembly of metal nanoparticles have been developed in order to harness their unique electrical and optical properties for device applications. This paper discusses a method for direct writing of Au nanoparticles at nanoscale resolution using dip-pen nanolithography. First, a procedure was developed for increasing the loading of Au nanoparticles onto AFM tips to prolong patterning life. AFM tips were subsequently imaged by scanning electron microscopy to determine ink coverage and to gain insight into the deposition process. Next, surface interactions, relative humidity, and writing speed were controlled to determine an optimal range of conditions for deposition. Various ink-substrate combinations were studied to elucidate the dependence of deposition on interactions between Au nanoparticles and the substrate surface; inks consisted of positively and negatively charged particles, and substrates were SiO(2) surfaces modified as hydrophilic or hydrophobic and interacted electrostatically or covalently with Au nanoparticles. Results indicate that a highly hydrophilic surface is required for Au nanoparticle deposition, unless covalent binding can occur between the Au and substrate surface. The optimal range of relative humidity for patterning was found to be 40-60%, and Au nanoparticle deposition was not sensitive to writing speeds ranging from 0.01 to 2 microm/s.

  View details for DOI 10.1021/nn8005416

  View details for Web of Science ID 000260503100022

  View details for PubMedID 19206460

• Synthesis of DNA-organic molecule-DNA triblock oligomers using the amide coupling reaction and their enzymatic amplification JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lee, J. K., Jung, Y. H., Stoltenberg, R. M., Tok, J. B., Bao, Z. 2008; 130 (39): 12854-?

  Abstract

  Precise electrical contact between single-molecule and electrodes is a first step to study single-molecule electronics and its application such as (bio)sensors and nanodevices. To realize a reliable electrical contact, we can use DNA as a template in the field of nanoelectronics because of its micrometer-scaled length with the thickness of nanometer-scale. In this paper, we studied the reactivity of the amide-coupling reaction to tether oligodeoxynucleotides (ODNs) to organic molecules and the elongation of the ODNs by the polymerase chain reaction (PCR) to synthesize 1.5 kbp dsDNA-organic molecule-1.5 kbp dsDNA (DOD) triblock architecture. The successful amide-coupling reactions were confirmed by electrospray ionization mass spectrometry (ESI-MS), and the triblock architectures were characterized by 1% agarose gel electrophoresis and atomic force microscope (AFM). Our result shows that this strategy is simple and makes it easy to construct DNA-organic molecule-DNA triblock architectures and potentially provides a platform to prepare and investigate single molecule electronics.

  View details for DOI 10.1021/ja8044458

  View details for Web of Science ID 000259553700009

  View details for PubMedID 18763775

• Aging Susceptibility of Terrace-Like Pentacene Films JOURNAL OF PHYSICAL CHEMISTRY C Yang, H., Yang, L., Ling, M., Lastella, S., Gandhi, D. D., Ramanath, G., Bao, Z., Ryu, C. V. 2008; 112 (42): 16161-16165

  View details for DOI 10.1021/jp8055224

  View details for Web of Science ID 000260129400001

• Water-stable organic transistors and their application in chemical and biological sensors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Roberts, M. E., Mannsfeld, S. C., Queralto, N., Reese, C., Locklin, J., Knoll, W., Bao, Z. 2008; 105 (34): 12134-12139

  Abstract

  The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

  View details for DOI 10.1073/pnas.0802105105

  View details for Web of Science ID 000258905700009

  View details for PubMedID 18711145

  View details for PubMedCentralID PMC2527878

• Trialkylsilylethynyl-functionalized tetraceno[2,3-b]thiophene and anthra[2,3-b]thiophene organic transistors CHEMISTRY OF MATERIALS Tang, M. L., Reichardt, A. D., Siegrist, T., Mannsfeld, S. C., Bao, Z. 2008; 20 (14): 4669-4676

  View details for DOI 10.1021/cm800644y

  View details for Web of Science ID 000257666300022

• Self-assembly, molecular packing, and electron transport in n-type polymer semiconductor nanobelts CHEMISTRY OF MATERIALS Briseno, A. L., Mannsfeld, S. C., Shamberger, P. J., Ohuchi, F. S., Bao, Z., Jenekhe, S. A., Xia, Y. 2008; 20 (14): 4712-4719

  View details for DOI 10.1021/cm8010265

  View details for Web of Science ID 000257666300027

• Self-sorted, aligned nanotube networks for thin-film transistors SCIENCE LeMieux, M. C., Roberts, M., Barman, S., Jin, Y. W., Kim, J. M., Bao, Z. 2008; 321 (5885): 101-104

  Abstract

  To find use in electronics, single-walled carbon nanotubes need to be efficiently separated by electronic type and aligned to ensure optimal and reproducible electronic properties. We report the fabrication of single-walled carbon nanotube (SWNT) network field-effect transistors, deposited from solution, possessing controllable topology and an on/off ratio as high as 900,000. The spin-assisted alignment and density of the SWNTs are tuned by different surfaces that effectively vary the degree of interaction with surface functionalities in the device channel. This leads to a self-sorted SWNT network in which nanotube chirality separation and simultaneous control of density and alignment occur in one step during device fabrication. Micro-Raman experiments corroborate device results as a function of surface chemistry, indicating enrichment of the specific SWNT electronic type absorbed onto the modified dielectric.

  View details for DOI 10.1126/science.1156588

  View details for Web of Science ID 000257320800045

  View details for PubMedID 18599781

• High-performance organic thin-film transistors through solution-sheared deposition of small-molecule organic semiconductors ADVANCED MATERIALS Becerril, H. A., Roberts, M. E., Liu, Z., Locklin, J., Bao, Z. 2008; 20 (13): 2588-?

  View details for DOI 10.1002/adma.200703120

  View details for Web of Science ID 000257808700022

• Organic solar cells with solution-processed graphene transparent electrodes APPLIED PHYSICS LETTERS Wu, J., Becerril, H. A., Bao, Z., Liu, Z., Chen, Y., Peumans, P. 2008; 92 (26)

  View details for DOI 10.1063/1.2924771

  View details for Web of Science ID 000257424500068

• Functionalized asymmetric linear acenes for high-performance organic semiconductors ADVANCED FUNCTIONAL MATERIALS Tang, M. L., Reichardt, A. D., Okamoto, T., Miyaki, N., Bao, Z. 2008; 18 (10): 1579-1585

  View details for DOI 10.1002/adfm.200701529

  View details for Web of Science ID 000256846400011

• Ambipolar, high performance, acene-based organic thin film transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Reichardt, A. D., Miyaki, N., Stoltenberg, R. M., Bao, Z. 2008; 130 (19): 6064-?

  Abstract

  We present a high performance, ambipolar organic field-effect transistor composed of a single material. Ambipolar molecules are rare, and they can enable low-power complementary-like circuits. This low band gap, asymmetric linear acene contains electron-withdrawing fluorine atoms, which lower the molecular orbital energies, allowing the injection of electrons. While hole and electron mobilities of up to 0.071 and 0.37 cm2/V.s, respectively, are reported on devices measured in nitrogen, hole mobilities of up to 0.12 cm2/V.s were found in ambient, with electron transport quenched. These devices were fabricated on octadecyltrimethoxysilane-treated surfaces at a substrate temperature of 60 degrees C.

  View details for DOI 10.1021/ja8005918

  View details for Web of Science ID 000255620200004

  View details for PubMedID 18412338

• Microstructure of oligofluorene asymmetric derivatives in orgranic thin film transistors CHEMISTRY OF MATERIALS Yuan, Q., Mannsfeld, S. C., Tang, M. L., Roberts, M., Toney, M. F., Delongchamp, D. M., Bao, Z. 2008; 20 (8): 2763-2772

  View details for DOI 10.1021/cm800071r

  View details for Web of Science ID 000255019300026

• Introducing organic nanowire transistors MATERIALS TODAY Briseno, A. L., Mannsfeld, S. C., Jenekhe, S. A., Bao, Z., Xia, Y. 2008; 11 (4): 38-47

  View details for Web of Science ID 000254691900020

• Thin film structure of tetraceno[2,3-b]thiophene characterized by grazing incidence X-ray scattering and near-edge X-ray absorption fine structure analysis JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Yuan, Q., Mannsfeld, S. C., Tang, M. L., Toney, M. F., Luening, J., Bao, Z. 2008; 130 (11): 3502-3508

  Abstract

  Understanding the structure-property relationship for organic semiconductors is crucial in rational molecular design and organic thin film process control. Charge carrier transport in organic field-effect transistors predominantly occurs in a few semiconductor layers close to the interface in contact with the dielectric layer, and the transport properties depend sensitively on the precise molecular packing. Therefore, a better understanding of the impact of molecular packing and thin film morphology in the first few monolayers above the dielectric layer on charge transport is needed to improve the transistor performance. In this Article, we show that the detailed molecular packing in thin organic semiconductor films can be solved through a combination of grazing incidence X-ray diffraction (GIXD), near-edge X-ray absorption spectra fine structure (NEXAFS) spectroscopy, energy minimization packing calculations, and structure refinement of the diffraction data. We solve the thin film structure for 2 and 20 nm thick films of tetraceno[2,3-b]thiophene and detect only a single phase for these thicknesses. The GIXD yields accurate unit cell dimensions, while the precise molecular arrangement in the unit cell was found from the energy minimization and structure refinement; the NEXAFS yields a consistent molecular tilt. For the 20 nm film, the unit cell is triclinic with a = 5.96 A, b = 7.71 A, c = 15.16 A, alpha = 97.30 degrees, beta = 95.63 degrees, gamma = 90 degrees; there are two molecules per unit cell with herringbone packing (49-59 degree angle) and tilted about 7 degrees from the substrate normal. The thin film structure is significantly different from the bulk single-crystal structure, indicating the importance of characterizing thin film to correlate with thin film device performance. The results are compared to the corresponding data for the chemically similar and widely used pentacene. Possible effects of the observed thin film structure and morphology on charge carrier mobility are discussed.

  View details for DOI 10.1021/ja0773002

  View details for Web of Science ID 000253951900062

  View details for PubMedID 18293975

• Evaluation of solution-processed reduced graphene oxide films as transparent conductors ACS NANO Becerril, H. A., Mao, J., Liu, Z., Stoltenberg, R. M., Bao, Z., Chen, Y. 2008; 2 (3): 463-470

  Abstract

  Processable, single-layered graphene oxide (GO) is an intriguing nanomaterial with tremendous potential for electronic applications. We spin-coated GO thin-films on quartz and characterized their sheet resistance and optical transparency using different reduction treatments. A thermal graphitization procedure was most effective, producing films with sheet resistances as low as 10(2) -10(3) Omega/square with 80% transmittance for 550 nm light. Our experiments demonstrate solution-processed GO films have potential as transparent electrodes.

  View details for DOI 10.1021/nn700375n

  View details for Web of Science ID 000254408000014

  View details for PubMedID 19206571

• Organic semiconductor-carbon nanotube bundle bilayer field effect transistors with enhanced mobilities and high on/off ratios APPLIED PHYSICS LETTERS Liu, S., Mannsfeld, S. C., LeMieux, M. C., Lee, H. W., Bao, Z. 2008; 92 (5)

  View details for DOI 10.1063/1.2841033

  View details for Web of Science ID 000253016500082

• "Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N '-bis(heptafluorobutyl)-3,4 : 9,10-perylene diimide"(vol 91, art no 212107, 2007) APPLIED PHYSICS LETTERS Oh, J. H., Liu, S., Bao, Z., Schmidt, R., Wuerthner, F. 2008; 92 (4)

  View details for DOI 10.1063/1.2839368

  View details for Web of Science ID 000252860400130

• Adding new functions to organic semiconductor nanowires by assembling metal nanoparticles onto their surfaces JOURNAL OF MATERIALS CHEMISTRY Briseno, A. L., Mannsfeld, S. C., Formo, E., Xiong, Y., Lu, X., Bao, Z., Jenekhe, S. A., Xia, Y. 2008; 18 (44): 5395-5398

  View details for DOI 10.1039/b809228c

  View details for Web of Science ID 000260620300014

• High performance organic thin film transistor through solution sheared deposition of small molecule organic semiconductors Adv. Mater. Becerril, H., A., Roberts, M., Liu, Z., Locklin, J., Bao, Z. 2008; 20: 2588-2594
• High-resolution measurement of the anisotropy of charge transport in single crystals ADVANCED MATERIALS Reese, C., Bao, Z. 2007; 19 (24): 4535-?

  View details for DOI 10.1002/adma.200701139

  View details for Web of Science ID 000252511500044

• Tunable thin-film crystalline structures and field-effect mobility of oligofluorene-thiophene derivatives CHEMISTRY OF MATERIALS Shin, T. J., Yang, H., Ling, M., Locklin, J., Yang, L., Lee, B., Roberts, M. E., Mallik, A. B., Bao, Z. 2007; 19 (24): 5882-5889

  View details for DOI 10.1021/cm0710599

  View details for Web of Science ID 000251150900022

• Enhancement in open circuit voltage through a cascade-type energy band structure APPLIED PHYSICS LETTERS Sista, S., Yao, Y., Yang, Y., Tang, M. L., Bao, Z. 2007; 91 (22)

  View details for DOI 10.1063/1.2817935

  View details for Web of Science ID 000251324600089

• Selective nucleation of organic single crystals from vapor phase on nanoscopically rough surfaces ADVANCED FUNCTIONAL MATERIALS Mannsfeld, S. C., Briseno, A. L., Liu, S., Reese, C., Roberts, M. E., Bao, Z. 2007; 17 (17): 3545-3553

  View details for DOI 10.1002/adfm.200700330

  View details for Web of Science ID 000251537300018

• Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N '-bis(heptafluorobutyl)3,4 : 9,10-perylene diimide APPLIED PHYSICS LETTERS Oh, J. H., Liu, S., Bao, Z., Schmidt, R., Wuerthner, F. 2007; 91 (21)

  View details for DOI 10.1063/1.2803073

  View details for Web of Science ID 000251105500020

• Core-fluorinated rerylene bisimide dyes: Air stable n-channel organic semiconductors for thin film transistors with exceptionally high on-to-off current ratios ADVANCED MATERIALS Schmidt, R., Ling, M. M., Oh, J. H., Winkler, M., Koenemann, M., Bao, Z., Wuerthner, F. 2007; 19 (21): 3692-?

  View details for DOI 10.1002/adma.200701478

  View details for Web of Science ID 000250992000051

• Synthesis, characterization, and field-effect transistor performance of pentacene derivatives ADVANCED MATERIALS Okamoto, T., Senatore, M. L., Ling, M., Mallik, A. B., Tang, M. L., Bao, Z. 2007; 19 (20): 3381-?

  View details for DOI 10.1002/adma.200700298

  View details for Web of Science ID 000250735600053

• Selective crystallization of organic semiconductors on patterned templates of carbon nanotubes ADVANCED FUNCTIONAL MATERIALS Liu, S., Briseno, A. L., Mannsfeld, S. C., You, W., Locklin, J., Lee, H. W., Xia, Y., Bao, Z. 2007; 17 (15): 2891-2896

  View details for DOI 10.1002/adfm.200700484

  View details for Web of Science ID 000250526300036

• Perylenediimide nanowires and their use in fabricating field-effect transistors and complementary inverters NANO LETTERS Briseno, A. L., Mannsfeld, S. C., Reese, C., Hancock, J. M., Xiong, Y., Jenekhe, S. A., Bao, Z., Xia, Y. 2007; 7 (9): 2847-2853

  Abstract

  Perylenetetracarboxyldiimide (PTCDI) nanowires self-assembled from commercially available materials are demonstrated as the n-channel semiconductor in organic field-effect transistors (OFETs) and as a building block in high-performance complementary inverters. Devices based on a network of PTCDI nanowires have electron mobilities and current on/off ratios on the order of 10(-2) cm2/Vs and 10(4), respectively. Complementary inverters based on n-channel PTCDI nanowire transistors and p-channel hexathiapentacene (HTP) nanowire OFETs achieved gains as high as 8. These results demonstrate the first example of the use of one-dimensional organic semiconductors in complementary inverters.

  View details for DOI 10.1021/nl071495u

  View details for Web of Science ID 000249501900055

  View details for PubMedID 17696562

• Synthesis of solution-soluble pentacene-containing conjugated copolymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Okamoto, T., Bao, Z. 2007; 129 (34): 10308-?

  View details for DOI 10.1021/ja0725403

  View details for Web of Science ID 000249035200005

  View details for PubMedID 17685520

• Probing the anisotropic field-effect mobility of solution-deposited dicyclohexyl-alpha-quaterthiophene single crystals ADVANCED FUNCTIONAL MATERIALS Mannsfeld, S. C., Locklin, J., Reese, C., Roberts, M. E., Lovinger, A. J., Bao, Z. 2007; 17 (10): 1617-1622

  View details for DOI 10.1002/adfm.200600865

  View details for Web of Science ID 000248062100004

• Solution-assisted assembly of organic semiconducting single crystals on surfaces with patterned wettability LANGMUIR Liu, S., Wang, W. M., Mannsfeld, S. C., Locklin, J., Erk, P., Gomez, M., Richter, F., Bao, Z. 2007; 23 (14): 7428-7432

  Abstract

  Two efficient approaches to assembling organic semiconducting single crystals are described. The methods rely on solvent wetting and dewetting on substrates with patterned wettability to selectively direct the deposition or removal of organic crystals. Substrates were functionalized with different self-assembled monolayers (SAMs) to achieve the desired wettabilities. The assembly of different organic crystals over centimeter-squared areas on Au, SiO2, and flexible plastic substrates was demonstrated. By designing line features on the substrate, the alignment of crystals, such as CuPc needles, was also achieved. As a demonstration of the potential application of this assembly approach, arrays of single-crystal organic field-effect transistors were fabricated by patterning organic single crystals directly onto and between transistor source and drain electrodes.

  View details for DOI 10.1021/1a700493p

  View details for Web of Science ID 000247487200004

  View details for PubMedID 17547427

• Solution deposited liquid crystalline semiconductors on a photoalignment layer for organic thin-film transistors APPLIED PHYSICS LETTERS Fujiwara, T., Locklin, J., Bao, Z. 2007; 90 (23)

  View details for DOI 10.1063/1.2746937

  View details for Web of Science ID 000247145500036

• Resistance switching in a polystyrene film containing Au nanoparticles JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Tsukamoto, T., Liu, S., Bao, Z. 2007; 46 (6A): 3622-3625

  View details for DOI 10.1143/JJAP.46.3622

  View details for Web of Science ID 000247493000070

• Correlating molecular structure to field-effect mobility: The investigation of side-chain functionality in phenylene - Thiophene oligomers and their application in field effect transistors CHEMISTRY OF MATERIALS Sung, A., Ling, M. M., Tang, M. L., Bao, Z., Locklin, J. 2007; 19 (9): 2342-2351

  View details for DOI 10.1021/cm070117n

  View details for Web of Science ID 000245900100031

• Air-stable n-channel organic semiconductors based on perylene diimide derivatives without strong electron withdrawing groups ADVANCED MATERIALS Ling, M., Erk, P., Gomez, M., Koenemann, M., Locklin, J., Bao, Z. 2007; 19 (8): 1123-1127

  View details for DOI 10.1002/adma.200601705

  View details for Web of Science ID 000246432800017

• Non-destructive probing of the anisotropy of field-effect mobility in the rubrene single crystal SYNTHETIC METALS Ling, M., Reese, C., Briseno, A. L., Bao, Z. 2007; 157 (6-7): 257-260

  View details for DOI 10.1016/j.synthmet.2007.02.004

  View details for Web of Science ID 000247520300003

• Organic single-crystal field-effect transistors MATERIALS TODAY Reese, C., Bao, Z. 2007; 10 (3): 20-27

  View details for Web of Science ID 000244597300016

• Fabrication of field-effect transistors from hexathiapentacene single-crystal nanowires NANO LETTERS Briseno, A. L., Mannsfeld, S. C., Lu, X., Xiong, Y., Jenekhe, S. A., Bao, Z., Xia, Y. 2007; 7 (3): 668-675

  Abstract

  This paper describes a simple, solution-phase route to the synthesis of bulk quantities of hexathiapentacene (HTP) single-crystal nanowires. These nanowires have also been successfully incorporated as the semiconducting material in field-effect transistors (FETs). For devices based on single nanowires, the carrier mobilities and current on/off ratios could be as high as 0.27 cm2/Vs and >103, respectively. For transistors fabricated from a network of nanowires, the mobilities and current on/off ratios could reach 0.057 cm2/Vs and >104, respectively. We have further demonstrated the use of nanowire networks in fabricating transistors on mechanically flexible substrates. Preliminary results show that these devices could withstand mechanical strain and still remain functional. The results from this study demonstrate the potential of utilizing solution-dispersible, nanostructured organic materials for use in low-cost, flexible electronic applications.

  View details for DOI 10.1021/nl0627036

  View details for Web of Science ID 000244867400023

  View details for PubMedID 17288487

• Complementary inverter using high mobility air-stable perylene di-imide derivatives APPLIED PHYSICS LETTERS Ling, M., Bao, Z., Erk, P., Koenemann, M., Gomez, M. 2007; 90 (9)

  View details for DOI 10.1063/1.2695873

  View details for Web of Science ID 000244591700107

• Air Stable n-Channel Organic Semiconductors for Thin Film Transistors Based on Fluorinated Derivatives of Perylene Diimides Chem. Mater. Chen, H., Z., Ling, M., M., Mo, X., Shi, M., M., Bao, Z. 2007; 19: 816-824
• Design, Synthesis, and Transistor Performance of Organic Semiconductors Organic Thin Film Transistors Mallik, A., B., Locklin, J., J., Mannsfeld, S., Reese, C., Roberts, M., Senatore, M. edited by Bao, Z., Locklin, J., J. CRC Press. 2007
• Solubility-driven thin film structures of regioregular poly(3-hexyl thiophene) using volatile solvents Appl. Phys. Lett. Yang, H., H., LeFevre, S., W., Ryu, C., Y., Bao, Z. 2007; 90: 172116
• Structural transitions of nanocrystalline domains in regioregular poly(3-hexyl thiophene) thin films J. Poly. Sci. Part B: Poly. Phys. Yang, H., C., Shin, T., J., Bao, Z., Ryu, C., Y. 2007; 45: 1303-1312
• Probing Non-destructive probing of the anisotropy of field-effect mobility in the rubrene single crystal Syn. Met. Ling, M., M., Reese, C., Briseno, L., Alejandro, Bao, Z. 2007; 157: 257-260
• Structure property relationships: Asymmetric oligofluorene-thiophene molecules for organic TFTs CHEMISTRY OF MATERIALS Tang, M. L., Roberts, M. E., Locklin, J. J., Ling, M. M., Meng, H., Bao, Z. 2006; 18 (26): 6250-6257

  View details for DOI 10.1021/cm0623514

  View details for Web of Science ID 000242935500028

• High-performance organic semiconductors: Asymmetric linear acenes containing sulphur JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Tang, M. L., Okamoto, T., Bao, Z. 2006; 128 (50): 16002-16003

  Abstract

  Two new linear acenes with fused thiophene units have been synthesized. These acenes have conjugation lengths between anthracene and pentacene. Thin films of these linear molecules were characterized by ultraviolet spectroscopy, X-ray diffraction, atomic force microscopy (AFM), and field-effect transistor measurements. Submonolayer AFM studies show growth that greatly resembles pentacene, while thin-film growth is dendritic. Mobilites as high as 0.47 cm2 V-1 s-1 have been found for the tetraceno[2,3-b]thiophene and are as high as 0.15 cm2 V-1 s-1 for anthra[2,3-b]thiophene.

  View details for DOI 10.1021/ja066824j

  View details for Web of Science ID 000242825600037

  View details for PubMedID 17165730

• Patterning organic single-crystal transistor arrays NATURE Briseno, A. L., Mannsfeld, S. C., Ling, M. M., Liu, S., Tseng, R. J., Reese, C., Roberts, M. E., Yang, Y., Wudl, F., Bao, Z. 2006; 444 (7121): 913-917

  Abstract

  Field-effect transistors made of organic single crystals are ideal for studying the charge transport characteristics of organic semiconductor materials. Their outstanding device performance, relative to that of transistors made of organic thin films, makes them also attractive candidates for electronic applications such as active matrix displays and sensor arrays. These applications require minimal cross-talk between neighbouring devices. In the case of thin film systems, simple patterning of the active semiconductor layer minimizes cross-talk. But when using organic single crystals, the only approach currently available for creating arrays of separate devices is manual selection and placing of individual crystals-a process prohibitive for producing devices at high density and with reasonable throughput. In contrast, inorganic crystals have been grown in extended arrays, and efficient and large-area fabrication of silicon crystalline islands with high mobilities for electronic applications has been reported. Here we describe a method for effectively fabricating large arrays of single crystals of a wide range of organic semiconductor materials directly onto transistor source-drain electrodes. We find that film domains of octadecyltriethoxysilane microcontact-printed onto either clean Si/SiO(2) surfaces or flexible plastic provide control over the nucleation of vapour-grown organic single crystals. This allows us to fabricate large arrays of high-performance organic single-crystal field-effect transistors with mobilities as high as 2.4 cm(2) V(-1) s(-1) and on/off ratios greater than 10(7), and devices on flexible substrates that retain their performance after significant bending. These results suggest that our fabrication approach constitutes a promising step that might ultimately allow us to utilize high-performance organic single-crystal field-effect transistors for large-area electronics applications.

  View details for DOI 10.1038/nature05427

  View details for Web of Science ID 000242805400052

  View details for PubMedID 17167482

• Hexathiapentacene: Structure, molecular packing, and thin-film transistors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Briseno, A. L., Miao, Q., Ling, M., Reese, C., Meng, H., Bao, Z., Wudl, F. 2006; 128 (49): 15576-15577

  Abstract

  In this communication we report the electrical characteristics of hexathiapentacene (HTP) and emphasize the unusual chemical structure and molecular packing. We report field-effect mobilities as high as 0.04 cm2 V-1 s-1 and current on/off ratios of >105. With crystallographic evidence of unusually long S-S bonds compared to normal S-S bonds, we have suggested a unique resonance structure similar to trithiapentalene, which well explains the bonding characteristics of HTP. This work appears to be the first to determine its molecular structure/packing mode and to study its application in organic transistors.

  View details for DOI 10.1021/ja066088j

  View details for Web of Science ID 000242575300014

  View details for PubMedID 17147352

• Assembly and alignment of metallic nanorods on surfaces with patterned wettability SMALL Liu, S., Tok, J. B., Locklin, J., Bao, Z. 2006; 2 (12): 1448-1453

  View details for DOI 10.1002/smll.200600275

  View details for Web of Science ID 000242275800011

  View details for PubMedID 17193004

• Copper hexafluorophthalocyanine field-effect transistors with enhanced mobility by soft contact lamination ORGANIC ELECTRONICS Ling, M., Bao, Z. 2006; 7 (6): 568-575

  View details for DOI 10.1016/j.orgel.2006.09.003

  View details for Web of Science ID 000242736700018

• High-performance organic semiconductors based on fluorene-phenylene oligomers with high ionization potentials ADVANCED MATERIALS Locklin, J., Ling, M. M., Sung, A., Roberts, M. E., Bao, Z. 2006; 18 (22): 2989-?

  View details for DOI 10.1002/adma.200601608

  View details for Web of Science ID 000242599600012

• High-performance microscale single-crystal transistors by lithography on an elastomer dielectric APPLIED PHYSICS LETTERS Reese, C., Chung, W., Ling, M., Roberts, M., Bao, Z. 2006; 89 (20)

  View details for DOI 10.1063/1.2388151

  View details for Web of Science ID 000242100200042

• Air-stable n-channel copper hexachlorophthalocyanine for field-effect transistors APPLIED PHYSICS LETTERS Ling, M., Bao, Z., Erk, P. 2006; 89 (16)

  View details for DOI 10.1063/1.2362976

  View details for Web of Science ID 000241405200123

• High-performance organic single-crystal transistors on flexible substrates ADVANCED MATERIALS Briseno, A. L., Tseng, R. J., Ling, M., Falcao, E. H., Yang, Y., Wudl, F., Bao, Z. 2006; 18 (17): 2320-?

  View details for DOI 10.1002/adma.200600634

  View details for Web of Science ID 000240573300024

• Organic single crystals: tools for the exploration of charge transport phenomena in organic materials JOURNAL OF MATERIALS CHEMISTRY Reese, C., Bao, Z. N. 2006; 16 (4): 329-333

  View details for DOI 10.1039/b509636g

  View details for Web of Science ID 000235034900001

• Effect of morphology on organic thin film transistor sensors ANALYTICAL AND BIOANALYTICAL CHEMISTRY Locklin, J., Bao, Z. N. 2006; 384 (2): 336-342

  Abstract

  This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.

  View details for DOI 10.1007/s00216-005-0137-z

  View details for Web of Science ID 000234299600004

  View details for PubMedID 16328249

• Thickness Dependence of Microstructure in Semiconducting Films of an Oligofluorene Derivative J. Am. Chem. Soc. DeLongchamp, D., M., Ling, M., M., Roberts, M., Jung, Y., S., Fischer, D., A., Lin, E., Bao, Z. 2006; 128: 16579-12586
• Transistor Performance of Top, Rough Surface of Pentacene Measured by Laminated, Double Insulated-Gate Supported on a Poly(dimethylsiloxanes) Base Structure Appl. Phys. Lett. Ling, M., M., Li, D., W., Bao, Z. 2006; 88: 33502
• Organic Single-Crystal Complementary Inverters Appl. Phys. Lett. Briseno, A., Tseng, R., Ling, M., Chen, H., Bao, Z., Falcao, E. 2006; 89: 222111
• Molecular conductance measurements through printed Au nanodots Appl. Phys. Lett. Jiang, W., Garfunkel, E., Zhitenev, N., B., Abusch-Magder, D., Tennant, D., M, Bao, Z. 2006; 89: 113107
• High Performance Organic Semiconductors Based on Fluorene-phenylene Oligomers with High Ionization Potentials Adv. Mater. Locklin, J., Ling, M., M., Sung, A., Roberts, M., Bao, Z. 2006; 18: 2989-2992
• High Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur J. Am. Chem. Soc. Tang, M., L., Okamoto, T., Bao, Z. 2006; 128: 160002-160003
• Patterning Organic Semiconductors Using ‘Dry’ Poly(dimethylsiloxane) Elastomeric Stamps for Thin Film Transistors J. Am. Chem. Soc. Briseno, A., L., Roberts, M., Ling, M., M., Moon, H., Bao, Z. 2006; 128: 3880-3881
• Control of Topography, Stress and Diffusion at Molecule-metal Interface Nanotechnology Zhitenev, N., B., Jiang, W., Erbe, A., Bao, Z., Garfunkel, E., Tennant, D., M 2006; 17: 1272-1277
• Organic Single Crystals: Tools for the Exploration of Charge Transport Phenomena in Organic Materials J. Mater. Chem. Reese, C., Bao, Z. 2006; 16: 329-333
• Optimizing the thin film morphology of organic field-effect transistors: The influence of molecular structure and vacuum deposition parameters on device performance POLYMER REVIEWS Locklin, J., Roberts, M. E., Mannsfeld, S. C., Bao, Z. 2006; 46 (1): 79-101

  View details for DOI 10.1080/15321790500471244

  View details for Web of Science ID 000240473300005

• Structure and bonding issues at the interface between gold and self-assembled conjugated dithiol monolayers LANGMUIR Jiang, W. R., Zhitenev, N., Bao, Z. N., Meng, H., Abusch-Magder, D., Tennant, D., Garfunkel, E. 2005; 21 (19): 8751-8757

  Abstract

  Organic thiols have received extensive attention recently because of their relative stability and ease of examination compared to other potential molecular electronic materials. In this work, scanning probe microscopy (SPM) is used to study (i) the structural properties of self-assembled monolayers (SAMs) containing conjugated dithiols and (ii) the formation of the upper molecule-metal interface on dithiol SAMs. The top gold film is deposited either by thermal evaporation or by nano-transfer printing (nTP). Generally, the utility of thermal evaporation is limited because of Au diffusion through the SAMs. However, several dithiol SAMs are identified in this work that bond well to Au overlayers and act as satisfactory diffusion barriers. Coassembly of conjugated dithiols and alkanemonothiols is suggested as a route to obtain dithiols that are denser packed and more vertical (than is obtained from pure dithiol routes). High-yield nTP is demonstrated on coassembled SAMs. Advantages and limitations of different Au deposition and transfer techniques are compared on a variety of length scales.

  View details for DOI 10.1021/la0474316

  View details for Web of Science ID 000231789800032

  View details for PubMedID 16142957

• Nanowire lithography: Fabricating controllable electrode gaps using Au-Ag-Au nanowires NANO LETTERS Liu, S. H., Tok, J. B., Bao, Z. N. 2005; 5 (6): 1071-1076

  Abstract

  A method to fabricate nanowire electrodes possessing controllable gaps is described. The method relies on electrochemical deposition and selective chemical etching or heating to selectively remove the Ag segment of Au-Ag-Au nanowires. Because the thickness of the Ag segment directly dictates the size of the nanogap, the gap width can be easily controlled during the nanowire fabrication process. Herein, we demonstrate gaps with 2 microm, 100 nm and 20 nm widths via the above-mentioned approaches. In addition, we observed that small gaps (approximately 20 nm) can be formed through annealing Au-Ag-Au nanowires at 200 degrees C in air. Electrical contact between nanowire electrodes and contact pads is studied. Using nanowire electrodes with a 100 nm gap, we subsequently fabricate organic field effect transistors (FETs) with regioregular poly(3-hexylthiophene).

  View details for DOI 10.1021/nl050581w

  View details for Web of Science ID 000229729900014

  View details for PubMedID 15943445

• Organic Thin Film Transistors Based on Cyclohexyl-substituted Organic Semiconductors Chem. Mater. Locklin, J., Li, D., W., Mannsfeld, S., C.B., Borkent, E., J., Meng, H., Advincula, R., Bao, Z. 2005; 17: 3366-3374
• Structure and Bonding Issues at the Interface between Gold and Self-Assembled Conjugated Dithiol Monolayers Langmuir Jiang, W., R., Zhitenev, N., Bao, Z., Meng, H., Abush-Magder, D., Tennant, D. 2005; 21: 8751-8757
• Molecular Nano-junctions Formed with Different Metallic Electrodes Nanotechnology Zhitenev, N., B., Erbe, A., Bao, Z., Jiang, W., Garfunkel, E. 2005; 16: 495-500
• Conducting AFM and 2D GIXD Studies on Pentacene Thin Films J. Am. Chem. Soc. Yang, H., Shin, T., J., Ling, M., M., Cho, K., Ryu, C., Y., Bao, Z. 2005; 127: 11542-11543
• Patterned Growth of Large Oriented Organic Semiconductor Single Crystals on Self-Assembled Monolayer Templates J. Am. Chem. Soc. Briseno, A., L., Aizenberg, J., Han, Y., J., Penkala, R., A., Moon, H., Lovinger, A., J., Bao, Z. 2005; 127: 2164-12165
• Effect of Mesoscale Crystalline Structure on Field-Effect Mobility of Regioregular Poly(3-hexyl thiophene) in Thin Film Transistors Adv. Func. Mater. Yang, H., Shin, T., J., Yang, L., Cho, K., Ryu, C., Y., Bao, Z. 2005; 15: 671-676
• Metallic contact formation for molecular electronics: interactions between vapor-deposited metals and self-assembled monolayers of conjugated mono- and dithiols LANGMUIR de Boer, B., Frank, M. M., Chabal, Y. J., Jiang, W. R., Garfunkel, E., Bao, Z. 2004; 20 (5): 1539-1542

  Abstract

  We present grazing-incidence Fourier transform infrared and AFM data of Au, Al, and Ti vapor-deposited onto self-assembled monolayers (SAMs) of conjugated mono- and dithiols. SAMs of 4,4'''-dimercapto-p-quaterphenyl, 4,4"-dimercapto-p-terphenyl, and 4,4'-dimercapto-p-biphenyl have reactive thiols at the SAM/vacuum interface that interact with vapor-deposited Au or Al atoms, preventing metal penetration. Conjugated monothiols lack such metal blocking groups, and metals (Au, Al) can penetrate into their SAMs. Vapor deposition of Ti onto conjugated mono- and dithiol SAMs and onto hexadecanethiol SAMs destroys the monolayers.

  View details for DOI 10.1021/la0356349

  View details for Web of Science ID 000189241500002

  View details for PubMedID 15801409

• Fine printing NATURE MATERIALS Bao, Z. N. 2004; 3 (3): 137-138

  View details for DOI 10.1038/nmat1079

  View details for Web of Science ID 000189345100010

  View details for PubMedID 14991010

• Organic light-emitting diodes formed by soft contact lamination PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Lee, T. W., Zaumseil, J., Bao, Z. N., Hsu, J. W., Rogers, J. A. 2004; 101 (2): 429-433

  Abstract

  Although tremendous progress has been made in organic light-emitting diodes (OLEDs), with few exceptions they are fabricated in the standard way by sequentially depositing active layers and electrodes onto a substrate. Here we describe a different approach for building OLEDs, which is based on physical lamination of thin metal electrodes supported by an elastomeric layer against an electroluminescent organic. This method relies only on van der Waals interactions to establish spatially homogeneous, intimate contacts between the electrodes and the organic. We find that devices fabricated in this manner have better performance than those constructed with standard processing techniques. The lamination approach avoids forms of disruption that can be introduced at the electrode/organic interface by metal evaporation and has a reduced sensitivity to pinhole or partial pinhole defects. In addition, because this form of "soft" contact lamination is intrinsically compatible with the techniques of soft lithography, it is easy to build patterned OLEDs with feature sizes into the nanometer regime. This method provides a new route to OLEDs for applications ranging from high performance displays to storage and lithography systems that rely on subwavelength light sources.

  View details for DOI 10.1073/pnas.0304179101

  View details for Web of Science ID 000188210400005

  View details for PubMedID 14704283

  View details for PubMedCentralID PMC327164

• Self-Aligned, Insulating-Layer Structure for Integrated Fabrication of Organic Self-Assembled Multilayer Electronic Devices Nanoletters Abe, T., Bao, Z., Sturm, J. 2004; 4: 2489-2492
• Synthesis, Crystal Structures and Transistor Performance of Tetracene Derivatives J. Am. Chem. Soc. Moon, H., Zeis, R., Borkent, E., J., Besnard, C., Lovinger, A., J., Siegrist, T., Bao, Z. 2004; 126: 15322-15323
• Synthesis of Polymer Dielectric Layers for Organic Thin Film Transistors via Surface-Initiated Ring-Opening Metathesis Polymerization J. Am. Chem. Soc. Rutenburg, I., Scherman, O., Bao, Z., Grubbs, R. 2004; 126: 4062-4063
• Thin Film Deposition, Patterning, and Printing in Organic Thin Film Transistors Chem. Mater. Ling, M., M., Bao, Z. 2004; 16: 4824-4840
• Single- and Multigrain Nanojunctions with a Self-Assembled Monolayer of Conjugated Molecules Phys. Rev. Lett. Zhitenev, N., B., Erbe, A., Bao, Z. 2004; 92: 186805-186806
• Organic Thin Film Transistors Materials Today Reese, C., Roberts, M., Ling, M., M., Bao, Z. 2004: 20-27
• Humidity Effect on Electrical Performance of Organic Thin-film Transistors Appl. Phys. Lett. Li, D., Borkent, E., J., Nortrup, R., Moon, H., Katz, H., E., Bao, Z. 2004; 86: 042104-042106
• Fine Printing Nature Materials Bao, Z. 2004; 3: 37-138
• Organic Light-emitting Diodes Formed by Soft Contact Lamination Proc. Nat. Acad. Sci. USA Lee, T., W., Zaumseil, J., Bao, Z., Hsu, J., Rogers, J., A. 2004; 101: 429-433
• Field-effect Transistors Made from Macroscopic Single Crystals of Tetracene and Related Semiconductors on Polymer Dielectrics J. Mater. Res. Katz, H., E., Kloc, C., Sundar, V., Zaumseil, J., Briseno, A., L., Bao, Z. 2004; 19: 1995
• Ambipolar Organic Thin Film Transistors of Cationic and Anionic Phthalocyanines Fabricated Using Layer-by-Layer Deposition from Aqueous Solution Chem. Mater. Locklin, J., Shinbo, K., Onishi, K., Kaneko, F., Bao, Z., Advincula, R., C. 2003; 15: 1404-1412
• Gated Molecular Devices Using Self-Assembled Monolayers Molecular Nanoelectronics Abush-Magder, D., Bao, Z., Erbe, A., Meng, H., Zhitenev, N, B. edited by Reed, M., Lee, T. 2003: 137–152
• Recent Materials Progress in Organic Electronics ACS Symposium Book "Polymers for microelectronics and nanoelectronics" Bao, Z. edited by Lin, Q., Pearson, R., A., Hedrick, J., C. Boston, MA, American Chemical Society. 2003
• Tetramethylpentacene: Remarkable Absence of Steric Effect on Field Effect Mobility Adv. Mater. Meng, H., Bendikov, M., Mitchell, G., Wudl, F., Bao, Z., Siegrist, T. 2003; 13 (15): 1090-1093
• Synthesis and Characterization of Conjugated Mono- and Dithiol Oligomers and Characterization of Their Self-Assembled Monolayers Langmuir Boer, B., de, Meng, H., Perepichka, D., F., Zheng, J., Chabal, Y., Wudl, F., Bao, Z. 2003; 19: 4272-4284
• Nanoscale Organic Transistors That Use Source/Drain Electrodes Supported by High Resolution Rubber Stamps Appl. Phys. Lett. Zaumseil, J., Someya, T., Bao, Z., Loo, Y., Y., Cirelli, R., Rogers, J., A. 2003; 5 (82): 793-795
• Gated Molecular Devices Using Self-assembled Monolayers Nanotechnology Zhitenev, N., B., Erbe, A., Meng, H., Bao, Z. 2003; 14: 254-257
• Oligofluorene-Thiophene Derivatives as High Performance Semiconductors for Organic Thin Film Transistors Chem. Mater. Meng, H., Zheng, J., Lovinger, A., J., Wang, B., C., Van Patten, P., G., Bao, Z. 2003; 15: 1778-1787
• Soft, conformable electrical contacts for organic semiconductors: High-resolution plastic circuits by lamination PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Loo, Y. L., Someya, T., Baldwin, K. W., Bao, Z. N., Ho, P., Dodabalapur, A., Katz, H. E., Rogers, J. A. 2002; 99 (16): 10252-10256

  Abstract

  Soft, conformable electrical contacts provide efficient, noninvasive probes for the transport properties of chemically and mechanically fragile, ultrathin organic semiconducting films. When combined with high-resolution printing and lamination techniques, these soft contacts also form the basis of a powerful technique for fabricating flexible plastic circuits. In this approach, a thin elastomeric film on a plastic substrate supports the electrodes and interconnections; laminating this substrate against another plastic substrate that supports the gate, dielectric and semiconductor levels establishes effective electrical contacts and completes the circuits. In addition to eliminating many of the problems associated with traditional layer-by-layer fabrication strategies, this lamination scheme possesses other attractive features: the transistors and circuit elements are naturally and efficiently encapsulated, and the active organic semiconductor layer is placed near the neutral mechanical plane. We demonstrate the features of soft, laminated contacts by fabricating large arrays of high-performance thin film transistors on plastic substrates by using a wide variety of organic semiconductors.

  View details for DOI 10.1073/pnas.162128299

  View details for Web of Science ID 000177343200008

  View details for PubMedID 12145323

  View details for PubMedCentralID PMC124899

• Integration and response of organic electronics with aqueous microfluidics LANGMUIR Someya, T., Dodabalapur, A., Gelperin, A., Katz, H. E., Bao, Z. 2002; 18 (13): 5299-5302

  View details for DOI 10.1021/la020026z

  View details for Web of Science ID 000176376100042

• Conductance of Small Molecular Junctions Phys. Rev. Lett. Zhitenev, N., B., Meng, H., Bao, Z. 2002; 88: 226801-226804
• Orthogonal Self-Aligned Electroless Metallization by Molecular Self-Assembly Langmuir Ho, P., Filas, R., Absuch-Megdar, D., Bao, Z. 2002; 18: 9625-9628
• Silsesquioxane Resins as High-Performance Solution Processible Dielectric Materials for Organic Transistor Applications Adv. Func. Mater. Bao, Z., Kuck, V., Rogers, J., A., Paczkowski, M. 2002; 12: 526-531
• Printed Plastic Electronics and Paperlike Displays J. Poly. Sci. Part A: Poly. Chem. Rogers, J., A., Bao, Z. 2002; 40: 3327-3334
• An In-Plane Anisotropic Organic Semiconductor Based Upon Poly(3-hexyl thiophene) Thin Solid Films Amundson, K., R., Sapjeta, B., J., Lovinger, A., J., Bao, Z. 2002; 414: 143-149
• Integration and Response of Organic Electronics with Aqueous Microfluidics Langmuir Someya, T., Dodabalapur, A., Gelperin, A., Katz, H., E., Bao, Z. 2002; 18: 5299-5302
• Photophysics of Anisotropic Shear-aligned Dendritic Side Group Phenylenevinylene Polymer J. Phys.: Condens. Matter Rothberg, L., J., Bao, Z. 2002; 14: 12261-12270
• Toward Controllable Self-assembly of Microstructures: Selective Functionalization and Fabrication of Patterned Spheres Chem. Mater. Bao, Z., Chen, X., L., Weldon, M., Chandross, E., A., Cherniavskaya, O., Dai, Y. 2002; 14: 24-26
• Space Charge Effects in Polymer-based Light-emitting Diodes Studied by Means of a Polarization Sensitive Electroreflectance Technique J. Appl. Phys. Michelotti, F., Bussi, S., Dominici, L., Bertolotti, M., Bao, Z. 2002; 91: 5521-5532
• Soft, Conformable Electrical Contacts for Organic Transistors: High Resolution Circuits by Lamination Loo, Y., L., Someya, T., Baldwin, K., W., Ho, P., Bao, Z., Dodabalapur, A. 2002
• Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Rogers, J. A., Bao, Z., Baldwin, K., Dodabalapur, A., Crone, B., Raju, V. R., Kuck, Katz, H., Amundson, K., Ewing, J., Drzaic, P. 2001; 98 (9): 4835-4840

  Abstract

  Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large ( approximately 5 x 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution ( approximately 1 microm) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing high-performance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature ( approximately 100 degrees C) annealing to increase the on/off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic "inks" to form sheets of electronic paper.

  View details for DOI 10.1073/pnas.091588098

  View details for Web of Science ID 000168311500008

  View details for PubMedID 11320233

  View details for PubMedCentralID PMC33123

• Soluble regioregular polythiophene derivatives as semiconducting materials for field-effect transistors CHEMISTRY OF MATERIALS Bao, Z. N., Lovinger, A. J. 1999; 11 (9): 2607-2612

  View details for Web of Science ID 000082706700051