Stanford Advisors


All Publications


  • Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability JOURNAL OF POLYMER SCIENCE Qian, Z., Galuska, L. A., Ma, G., McNutt, W. W., Zhang, S., Mei, J., Gu, X. 2021
  • Ultra-conformal skin electrodes with synergistically enhanced conductivity for long-time and low-motion artifact epidermal electrophysiology NATURE COMMUNICATIONS Zhao, Y., Zhang, S., Yu, T., Zhang, Y., Ye, G., Cui, H., He, C., Jiang, W., Zhai, Y., Lu, C., Gu, X., Liu, N. 2021; 12 (1): 4880

    Abstract

    Accurate and imperceptible monitoring of electrophysiological signals is of primary importance for wearable healthcare. Stiff and bulky pregelled electrodes are now commonly used in clinical diagnosis, causing severe discomfort to users for long-time using as well as artifact signals in motion. Here, we report a ~100 nm ultra-thin dry epidermal electrode that is able to conformably adhere to skin and accurately measure electrophysiological signals. It showed low sheet resistance (~24 Ω/sq, 4142 S/cm), high transparency, and mechano-electrical stability. The enhanced optoelectronic performance was due to the synergistic effect between graphene and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which induced a high degree of molecular ordering on PEDOT and charge transfer on graphene by strong π-π interaction. Together with ultra-thin nature, this dry epidermal electrode is able to accurately monitor electrophysiological signals such as facial skin and brain activity with low-motion artifact, enabling human-machine interfacing and long-time mental/physical health monitoring.

    View details for DOI 10.1038/s41467-021-25152-y

    View details for Web of Science ID 000686181800026

    View details for PubMedID 34385444

    View details for PubMedCentralID PMC8361161

  • Water-assisted mechanical testing of polymeric thin-films JOURNAL OF POLYMER SCIENCE Zhang, S., Galuska, L. A., Gu, X. 2021
  • Enhancing the Solubility of Semiconducting Polymers in Eco-Friendly Solvents with Carbohydrate-Containing Side Chains. ACS applied materials & interfaces Mooney, M., Wang, Y., Nyayachavadi, A., Zhang, S., Gu, X., Rondeau-Gagne, S. 2021; 13 (21): 25175-25185

    Abstract

    Semiconducting polymers are at the forefront of next-generation organic electronics due to their robust mechanical and optoelectronic properties. However, their extended pi-conjugation often leads to materials with low solubilities in common organic solvents, thus requiring processing in high-boiling-point and toxic halogenated solvents to generate thin-film devices. To address this environmental concern, a natural product-inspired side-chain engineering approach was used to incorporate galactose-containing moieties into semiconducting polymers toward improved processability in greener solvents. Novel isoindigo-based polymers with different ratios of galactose-containing side chains were synthesized to improve the solubilities of the organic semiconductors in alcohol-based solvents. The addition of carbohydrate-containing side chains to pi-conjugated polymers was found to considerably impact the intermolecular aggregation of the materials and their microstructures in the solid state as confirmed by atomic force microscopy and grazing-incidence wide-angle X-ray scattering. The charge transport characteristics of the new semiconductors were evaluated by the fabrication of organic field-effect transistors prepared from both toxic halogenated and greener alcohol-based solvents. Importantly, the incorporation of carbohydrate-containing side chains was shown to have very little detrimental impact on the electronic properties of the polymer when processed from green solvents.

    View details for DOI 10.1021/acsami.1c02860

    View details for PubMedID 34006092

  • SMART transfer method to directly compare the mechanical response of water-supported and free-standing ultrathin polymeric films NATURE COMMUNICATIONS Galuska, L. A., Muckley, E. S., Cao, Z., Ehlenberg, D. F., Qian, Z., Zhang, S., Rondeau-Gagne, S., Phan, M. D., Ankner, J. F., Ivanov, I. N., Gu, X. 2021; 12 (1): 2347

    Abstract

    Intrinsic mechanical properties of sub-100 nm thin films are markedly difficult to obtain, yet an ever-growing necessity for emerging fields such as soft organic electronics. To complicate matters, the interfacial contribution plays a major role in such thin films and is often unexplored despite supporting substrates being a main component in current metrologies. Here we present the shear motion assisted robust transfer technique for fabricating free-standing sub-100 nm films and measuring their inherent structural-mechanical properties. We compare these results to water-supported measurements, exploring two phenomena: 1) The influence of confinement on mechanics and 2) the role of water on the mechanical properties of hydrophobic films. Upon confinement, polystyrene films exhibit increased strain at failure, and reduced yield stress, while modulus is reduced only for the thinnest 19 nm film. Water measurements demonstrate subtle differences in mechanics which we elucidate using quartz crystal microbalance and neutron reflectometry.

    View details for DOI 10.1038/s41467-021-22473-w

    View details for Web of Science ID 000642510700005

    View details for PubMedID 33879775

    View details for PubMedCentralID PMC8058343

  • Engineering donor-acceptor conjugated polymers for high-performance and fast-response organic electrochemical transistors dagger JOURNAL OF MATERIALS CHEMISTRY C Jia, H., Huang, Z., Li, P., Zhang, S., Wang, Y., Wang, J., Gu, X., Lei, T. 2021; 9 (14): 4927-4934

    View details for DOI 10.1039/d1tc00440a

    View details for Web of Science ID 000635214900001

  • Efficient n-Doping of Polymeric Semiconductors through Controlling the Dynamics of Solution-State Polymer Aggregates ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Xiong, M., Yan, X., Li, J., Zhang, S., Cao, Z., Prine, N., Lu, Y., Wang, J., Gu, X., Lei, T. 2021; 60 (15): 8189-8197

    Abstract

    Doping of polymeric semiconductors limits the miscibility between polymers and dopants. Although significant efforts have been devoted to enhancing miscibility through chemical modification, the electrical conductivities of n-doped polymeric semiconductors are usually below 10 S cm-1 . We report a different approach to overcome the miscibility issue by modulating the solution-state aggregates of conjugated polymers. We found that the solution-state aggregates of conjugated polymers not only changed with solvent and temperature but also changed with solution aging time. Modulating the solution-state polymer aggregates can directly influence their solid-state microstructures and miscibility with dopants. As a result, both high doping efficiency and high charge-carrier mobility were simultaneously obtained. The n-doped electrical conductivity of P(PzDPP-CT2) can be tuned up to 32.1 S cm-1 . This method can also be used to improve the doping efficiency of other polymer systems (e.g. N2200) with different aggregation tendencies and behaviors.

    View details for DOI 10.1002/anie.202015216

    View details for Web of Science ID 000624626300001

    View details for PubMedID 33403799

  • Spontaneously supersaturated nucleation strategy for high reproducible and efficient perovskite solar cells CHEMICAL ENGINEERING JOURNAL Li, B., Zhang, Q., Zhang, S., Ahmad, Z., Chidanguro, T., Davis, A., Simon, Y. C., Gu, X., Zheng, W., Pradhan, N., Dai, Q. 2021; 405
  • 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
  • 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
  • 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
  • Wafer-Scale Fabrication of High-Performance n-Type Polymer Monolayer Transistors Using a Multi-Level Self-Assembly Strategy ADVANCED MATERIALS Yao, Z., Zheng, Y., Li, Q., Lei, T., Zhang, S., Zou, L., Liu, H., Dou, J., Lu, Y., Wang, J., Gu, X., Pei, J. 2019; 31 (7)
  • Wafer-Scale Fabrication of High-Performance n-Type Polymer Monolayer Transistors Using a Multi-Level Self-Assembly Strategy. Advanced materials (Deerfield Beach, Fla.) Yao, Z., Zheng, Y., Li, Q., Lei, T., Zhang, S., Zou, L., Liu, H., Dou, J., Lu, Y., Wang, J., Gu, X., Pei, J. 2018: e1806747

    Abstract

    Wafer-scale fabrication of high-performance uniform organic electronic materials is of great challenge and has rarely been realized before. Previous large-scale fabrication methods always lead to different layer thickness and thereby poor film and device uniformity. Herein, the first demonstration of 4 in. wafer-scale, uniform, and high-performance n-type polymer monolayer films is reported, enabled by controlling the multi-level self-assembly process of conjugated polymers in solution. Since the self-assembly process happened in solution, the uniform 2D polymer monolayers can be facilely deposited on various substrates, and theoretically without size limitations. Polymer monolayer transistors exhibit high electron mobilities of up to 1.88 cm2 V-1 s-1 , which is among the highest in n-type monolayer organic transistors. This method allows to easily fabricate n-type conjugated polymers with wafer-scale, high uniformity, low contact resistance, and excellent transistor performance (better than the traditional spin-coating method). This work provides an effective strategy to prepare large-scale and uniform 2D polymer monolayers, which could enable the application of conjugated polymers for wafer-scale sophisticated electronics.

    View details for PubMedID 30549332