Apurva Mehta

All Publications

• Active Learning for Rapid Targeted Synthesis of Compositionally Complex Alloys MATERIALS Johnson, N. S., Mishra, A., Kirsch, D. J., Mehta, A. 2024; 17 (16)

  Abstract

  The next generation of advanced materials is tending toward increasingly complex compositions. Synthesizing precise composition is time-consuming and becomes exponentially demanding with increasing compositional complexity. An experienced human operator does significantly better than a novice but still struggles to consistently achieve precision when synthesis parameters are coupled. The time to optimize synthesis becomes a barrier to exploring scientifically and technologically exciting compositionally complex materials. This investigation demonstrates an active learning (AL) approach for optimizing physical vapor deposition synthesis of thin-film alloys with up to five principal elements. We compared AL-based on Gaussian process (GP) and random forest (RF) models. The best performing models were able to discover synthesis parameters for a target quinary alloy in 14 iterations. We also demonstrate the capability of these models to be used in transfer learning tasks. RF and GP models trained on lower dimensional systems (i.e., ternary, quarternary) show an immediate improvement in prediction accuracy compared to models trained only on quinary samples. Furthermore, samples that only share a few elements in common with the target composition can be used for model pre-training. We believe that such AL approaches can be widely adapted to significantly accelerate the exploration of compositionally complex materials.

  View details for DOI 10.3390/ma17164038

  View details for Web of Science ID 001304748500001

  View details for PubMedID 39203216

  View details for PubMedCentralID PMC11355945

• Superconducting phase diagram in BixNi1-x<i> x</i> Ni 1-<i> x</i> thin films: The effects of Bi stoichiometry on superconductivity PHYSICAL REVIEW MATERIALS Park, J., Horn, J. A., Kirsch, D. J., Pant, R. K., Yoon, H., Baek, S., Sarker, S., Mehta, A., Zhang, X., Lee, S., Greene, R., Paglione, J., Takeuchi, I. 2024; 8 (7)

  View details for DOI 10.1103/PhysRevMaterials.8.074805

  View details for Web of Science ID 001281756200002

• Probabilistic Mixture Model-Based Spectral Unmixing APPLIED SCIENCES-BASEL Hoidn, O., Mishra, A., Mehta, A. 2024; 14 (11)

  View details for DOI 10.3390/app14114836

  View details for Web of Science ID 001245642000001

• A Case Study of Multimodal, Multi-institutional Data Management for the Combinatorial Materials Science Community INTEGRATING MATERIALS AND MANUFACTURING INNOVATION Allec, S. I., Muckley, E. S., Johnson, N. S., Borg, C. H., Kirsch, D. J., Martin, J., Pant, R., Takeuchi, I., Lee, A. S., Saal, J. E., Ward, L., Mehta, A. 2024

  View details for DOI 10.1007/s40192-024-00345-7

  View details for Web of Science ID 001190232000001

• A general indicator for the tolerance to impurities of metals and alloys MATERIALIA Lund, E., Huang, S., Kube, S. A., Liu, G., Johnson, N., Colley, W., Mehta, A., Reck, B. K., Sohn, S., Schroers, J. 2024; 33

  View details for DOI 10.1016/j.mtla.2024.102037

  View details for Web of Science ID 001218670000001

• Physics constrained unsupervised deep learning for rapid, high resolution scanning coherent diffraction reconstruction. Scientific reports Hoidn, O., Mishra, A. A., Mehta, A. 2023; 13 (1): 22789

  Abstract

  By circumventing the resolution limitations of optics, coherent diffractive imaging (CDI) and ptychography are making their way into scientific fields ranging from X-ray imaging to astronomy. Yet, the need for time consuming iterative phase recovery hampers real-time imaging. While supervised deep learning strategies have increased reconstruction speed, they sacrifice image quality. Furthermore, these methods' demand for extensive labeled training data is experimentally burdensome. Here, we propose an unsupervised physics-informed neural network reconstruction method, PtychoPINN, that retains the factor of 100-to-1000 speedup of deep learning-based reconstruction while improving reconstruction quality by combining the diffraction forward map with real-space constraints from overlapping measurements. In particular, PtychoPINN gains a factor of 4 in linear resolution and an 8 dB improvement in PSNR while also accruing improvements in generalizability and robustness. This blend of performance and computational efficiency offers exciting prospects for high-resolution real-time imaging in high-throughput environments such as X-ray free electron lasers (XFELs) and diffraction-limited light sources.

  View details for DOI 10.1038/s41598-023-48351-7

  View details for PubMedID 38123573

• Effects of elevated-temperature deposition on the atomic structure of amorphous Ta₂O₅ films APL MATERIALS Prasai, K., Lee, K., Baloukas, B., Cheng, H., Fazio, M., Martinu, L., Mehta, A., Menoni, C. S., Schiettekatte, F., Shink, R., Shyam, B., Vajente, G., Fejer, M. M., Bassiri, R. 2023; 11 (12)

  View details for DOI 10.1063/5.0170100

  View details for Web of Science ID 001127548400002

• Tuning In-Plane Magnetic Anisotropy and Interfacial Exchange Coupling in Epitaxial La_2/3Sr_1/3CoO₃/La_2/3Sr_1/3MnO₃ Heterostructures ACS APPLIED MATERIALS & INTERFACES Feng, M., Ahlm, N., Sasaki, D. Y., Chiu, I., N'Diaye, A. T., Shafer, P., Klewe, C., Mehta, A., Takamura, Y. 2023; 15 (45): 53086-53095

  Abstract

  Controlling the in-plane magnetocrystalline anisotropy and interfacial exchange coupling between ferromagnetic (FM) layers plays a key role in next-generation spintronic and magnetic memory devices. In this work, we explored the effect of tuning the magnetocrystalline anisotropy of La2/3Sr1/3CoO3 (LSCO) and La2/3Sr1/3MnO3 (LSMO) layers and the corresponding effect on interfacial exchange coupling by adjusting the thickness of the LSCO layer (tLSCO). The epitaxial LSCO/LSMO bilayers were grown on (110)o-oriented NdGaO3 (NGO) substrates with a fixed LSMO (top layer) thickness of 6 nm and LSCO (bottom layer) thicknesses varying from 1 to 10 nm. Despite the small difference (∼0.2%) in lattice mismatch between the two in-plane directions, [001]o and [11̅0]o, a pronounced in-plane magnetic anisotropy was observed. Soft X-ray magnetic circular dichroism hysteresis loops revealed that for tLSCO ≤ 4 nm, the easy axes for both LSCO and LSMO layers were along the [001]o direction, and the LSCO layer was characterized by magnetically active Co2+ ions that strongly coupled to the LSMO layer. No exchange bias effect was observed in the hysteresis loops. In contrast, along the [11̅0]o direction, the LSCO and LSMO layers displayed a small difference in their coercivity values, and a small exchange bias shift was observed. As tLSCO increased above 4 nm, the easy axis for the LSCO layer remained along the [100]o direction, but it gradually rotated to the [11̅0]o direction for the LSMO layer, resulting in a large negative exchange bias shift. Therefore, we provide a way to control the magnetocrystalline anisotropy and exchange bias by tuning the interfacial exchange coupling between the two FM layers.

  View details for DOI 10.1021/acsami.3c10376

  View details for Web of Science ID 001096840500001

  View details for PubMedID 37910813

  View details for PubMedCentralID PMC10658449

• Two Pathways for the Degradation of Orpiment Pigment (As2S3) Found in Paintings JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Broers, F. H., Janssens, K., Weker, J., Webb, S. M., Mehta, A., Meirer, F., Keune, K. 2023; 145 (16): 8847-8859

  Abstract

  Paintings are complex objects containing many different chemical compounds that can react over time. The degradation of arsenic sulfide pigments causes optical changes in paintings. The main degradation product was thought to be white arsenolite (As2O3), but previous research also showed the abundant presence of As(V) species. In this study, we investigate the influence of the presence of a medium on the degradation mechanism of orpiment (As2S3) using synchrotron radiation (SR)-based tomographic transmission X-ray microscopy, SR-based micro-X-ray fluorescence, and X-ray absorption near edge structure spectroscopy. Upon direct illumination of dry orpiment powder using UV-visible light, only the formation of As2O3 was observed. When As2S3 was surrounded by a medium and illuminated, As2O3 was only observed in the area directly exposed to light, while As(V) degradation species were found elsewhere in the medium. Without accelerated artificial light aging, As(V)(aq) species are formed and migrate throughout the medium within weeks after preparation. In both scenarios, the As(V) species form via intermediate As(III)(aq) species and the presence of a medium is necessary. As(V)(aq) species can react with available cations to form insoluble metal arsenates, which induces stress within the paint layers (leading to, e.g., cracks and delamination) or can lead to a visual change of the image of the painting.

  View details for DOI 10.1021/jacs.2c12271

  View details for Web of Science ID 000974346900001

  View details for PubMedID 37058004

  View details for PubMedCentralID PMC10141271

• Magnetic phase diagram mapping in Fe1-xRhx composition-spread thin films JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A Yu, H., Gao, T., N'Diaye, A. T., Arenholz, E., Sarker, S., Mehta, A., Zhang, X., Takeuchi, I. 2023; 41 (2)

  View details for DOI 10.1116/6.0002220

  View details for Web of Science ID 000932377600002

• Local ordering in Ge/Ge-Sn semiconductor alloy core/shell nanowires revealed by extended x-ray absorption fine structure (EXAFS) APPLIED PHYSICS LETTERS Lentz, J., Woicik, J. C., Bergschneider, M., Davis, R., Mehta, A., Cho, K., McIntyre, P. C. 2023; 122 (6)

  View details for DOI 10.1063/5.0136746

  View details for Web of Science ID 000932386200011

• Author Correction: Discovery of LaAlO3 as an efficient catalyst for two-electron water electrolysis towards hydrogen peroxide. Nature communications Baek, J., Jin, Q., Johnson, N. S., Jiang, Y., Ning, R., Mehta, A., Siahrostami, S., Zheng, X. 2022; 13 (1): 7685

  View details for DOI 10.1038/s41467-022-35478-w

  View details for PubMedID 36509777

• Discovery of LaAlO3 as an efficient catalyst for two-electron water electrolysis towards hydrogen peroxide. Nature communications Baek, J., Jin, Q., Johnson, N. S., Jiang, Y., Ning, R., Mehta, A., Siahrostami, S., Zheng, X. 2022; 13 (1): 7256

  Abstract

  Electrochemical two-electron water oxidation reaction (2e-WOR) has drawn significant attention as a promising process to achieve the continuous on-site production of hydrogen peroxide (H2O2). However, compared to the cathodic H2O2 generation, the anodic 2e-WOR is more challenging to establish catalysts due to the severe oxidizing environment. In this study, we combine density functional theory (DFT) calculations with experiments to discover a stable and efficient perovskite catalyst for the anodic 2e-WOR. Our theoretical screening efforts identify LaAlO3 perovskite as a stable, active, and selective candidate for catalyzing 2e-WOR. Our experimental results verify that LaAlO3 achieves an overpotential of 510mV at 10mAcm-2 in 4M K2CO3/KHCO3, lower than those of many reported metal oxide catalysts. In addition, LaAlO3 maintains a stable H2O2 Faradaic efficiency with only a 3% decrease after 3h at 2.7V vs. RHE. This computation-experiment synergistic approach introduces another effective direction to discover promising catalysts for the harsh anodic 2e-WOR towards H2O2.

  View details for DOI 10.1038/s41467-022-34884-4

  View details for PubMedID 36433962

• Strain- and thickness-dependent magnetic properties of epitaxial La_0.67Sr_0.33CoO₃/La_0.67Sr_0.33MnO₃ bilayers JOURNAL OF APPLIED PHYSICS Feng, M., Ahlm, N. J., Kane, A. M., Chiu, I., Sasaki, D. Y., Shafer, P., N'Diaye, A. T., Mehta, A., Takamura, Y. 2022; 132 (19)

  View details for DOI 10.1063/5.0122009

  View details for Web of Science ID 000885383200015

• Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia-Zirconia Alloys. ACS applied materials & interfaces Yu, Z., Saini, B., Liu, Y., Huang, F., Mehta, A., Baniecki, J. D., Wong, H. P., Tsai, W., McIntyre, P. C. 2022

  Abstract

  Hafnia-based ferroelectric thin films are promising for semiconductor memory and neuromorphic computing applications. Amorphous, as-deposited, thin-film binary alloys of HfO2 and ZrO2 transform to the metastable, orthorhombic ferroelectric phase during post-deposition annealing and cooling. This transformation is generally thought to involve formation of a tetragonal precursor phase that distorts into the orthorhombic phase during cooling. In this work, we systematically study the effects of atomic layer deposition (ALD) temperature on the ferroelectricity of post-deposition-annealed Hf0.5Zr0.5O2 (HZO) thin films. Seed crystallites having interplanar spacings consistent with the polar orthorhombic phase are observed by a plan-view transmission electron microscope in HZO thin films deposited at an elevated ALD temperature. After ALD under conditions that promote formation of these nanocrystallites, high-polarization (Pr > 18 muC/cm2) ferroelectric switching is observed after rapid thermal annealing (RTA) at low temperature (350 °C). These results indicate the presence of minimal non-ferroelectric phases retained in the films after RTA when the ALD process forms nanocrystalline particles that seed subsequent formation of the polar orthorhombic phase.

  View details for DOI 10.1021/acsami.2c15047

  View details for PubMedID 36384298

• Atomic-Layer-Deposited Aluminum Oxide Thin Films Probed with X-ray Scattering and Compared to Molecular Dynamics and Density Functional Theory Models ACS OMEGA Pugliese, A., Shyam, B., Repa, G. M., Nguyen, A., Mehta, A., Webb, E. B., Fredin, L. A., Strandwitz, N. C. 2022; 7 (45): 41033-41043

  Abstract

  A better understanding of amorphous aluminum oxide's structure and electronic properties is obtained through combined experimental and computational approaches. Grazing incidence X-ray scattering measurements were carried out on aluminum oxide thin films grown using thermal atomic layer deposition. The corresponding pair distribution functions (PDFs) showed structures similar to previously reported PDFs of solid-state amorphous alumina and molten alumina. Structural models based on crystalline alumina polymorphs (PDFgui) and amorphous alumina (molecular dynamics, MD) were examined for structural comparisons to the experimental PDF data. Smaller MD models were optimized and verified against larger models to allow for quantum chemical electronic structure calculations. The electronic structure of the amorphous alumina models yields additional insight into the band structure and electronic defects present in amorphous alumina that are not present in crystalline samples.

  View details for DOI 10.1021/acsomega.2c04402

  View details for Web of Science ID 000882617200001

  View details for PubMedID 36406558

  View details for PubMedCentralID PMC9670265

• Machine learned synthesizability predictions aided by density functional theory COMMUNICATIONS MATERIALS Lee, A., Sarker, S., Saal, J., Ward, L., Borg, C., Mehta, A., Wolverton, C. 2022; 3 (1)

  View details for DOI 10.1038/s43246-022-00295-7

  View details for Web of Science ID 000866470800001

• Thin-Film Paradigm to Probe Interfacial Diffusion during Solid-State Metathesis Reactions CHEMISTRY OF MATERIALS McAuliffe, R. D., Huang, G., Montiel, D., Mehta, A., Davis, R. C., Petrova, V., Browning, K. L., Neilson, J. R., Liu, P., Thornton, K., Veith, G. M. 2022; 34 (14): 6279-6287

  View details for DOI 10.1021/acs.chemmater.2c00303

  View details for Web of Science ID 000834138700001

• Giant Orbital Anisotropy with Strong Spin-Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Kim, S., Pathak, S., Rhim, S. H., Cha, J., Jekal, S., Hong, S. C., Lee, H. H., Park, S., Lee, H., Park, J., Lee, S., Steinruck, H., Mehta, A., Wang, S. X., Hong, J. 2022: e2201749

  Abstract

  Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin-orbit-related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low-energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3 O4 /Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3 O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin-orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature-dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin-orbit coupling at the interface is key to exploring spintronic devices with new functionalities.

  View details for DOI 10.1002/advs.202201749

  View details for PubMedID 35748161

• Mapping Thermoelectric Transport in a Multicomponent Alloy Space ADVANCED ELECTRONIC MATERIALS Gurunathan, R., Sarker, S., Borg, C. H., Saal, J., Ward, L., Mehta, A., Snyder, G. 2022

  View details for DOI 10.1002/aelm.202200327

  View details for Web of Science ID 000814466700001

• Towards Automated Design of Corrosion Resistant Alloy Coatings with an Autonomous Scanning Droplet Cell JOM DeCost, B., Joress, H., Sarker, S., Mehta, A., Hattrick-Simpers, J. 2022; 74 (8): 2941-2950

  View details for DOI 10.1007/s11837-022-05367-0

  View details for Web of Science ID 000814022900001

• Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors. Nature Cheema, S. S., Shanker, N., Wang, L., Hsu, C., Hsu, S., Liao, Y., San Jose, M., Gomez, J., Chakraborty, W., Li, W., Bae, J., Volkman, S. K., Kwon, D., Rho, Y., Pinelli, G., Rastogi, R., Pipitone, D., Stull, C., Cook, M., Tyrrell, B., Stoica, V. A., Zhang, Z., Freeland, J. W., Tassone, C. J., Mehta, A., Saheli, G., Thompson, D., Suh, D. I., Koo, W., Nam, K., Jung, D. J., Song, W., Lin, C., Nam, S., Heo, J., Parihar, N., Grigoropoulos, C. P., Shafer, P., Fay, P., Ramesh, R., Mahapatra, S., Ciston, J., Datta, S., Mohamed, M., Hu, C., Salahuddin, S. 2022; 604 (7904): 65-71

  Abstract

  With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage1. This led to a fundamental changein the gate stack in 2008,the incorporation of high-dielectric-constant HfO2(ref.2), which remains the material of choiceto date. Here we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20angstroms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO2 thickness of approximately 6.5angstroms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-dielectric-constant gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current3. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO2-based high-dielectric-constant materials.

  View details for DOI 10.1038/s41586-022-04425-6

  View details for PubMedID 35388197

• CeO2 Doping of Hf0.5Zr0.5O2 Thin Films for High Endurance Ferroelectric Memories ADVANCED ELECTRONIC MATERIALS Yu, Z., Saini, B., Liao, P., Chang, Y., Hou, D., Nien, C., Shih, Y., Yeong, S., Afanas'ev, V., Huang, F., Baniecki, J. D., Mehta, A., Chang, C., Wong, H., Tsai, W., McIntyre, P. C. 2022

  View details for DOI 10.1002/aelm.202101258

  View details for Web of Science ID 000770370800001

• Discovering exceptionally hard and wear-resistant metallic glasses by combining machine-learning with high throughput experimentation APPLIED PHYSICS REVIEWS Sarker, S., Tang-Kong, R., Schoeppner, R., Ward, L., Hasan, N., Van Campen, D. G., Takeuchi, I., Hattrick-Simpers, J., Zakutayev, A., Packard, C. E., Mehta, A. 2022; 9 (1)

  View details for DOI 10.1063/5.0068207

  View details for Web of Science ID 000741081100001

• Physics in the Machine: Integrating Physical Knowledge in Autonomous Phase-Mapping FRONTIERS IN PHYSICS Kusne, A., McDannald, A., DeCost, B., Oses, C., Toher, C., Curtarolo, S., Mehta, A., Takeuchi, I. 2022; 10

  View details for DOI 10.3389/fphy.2022.815863

  View details for Web of Science ID 000767779100001

• Autonomous experimentation systems for materials development: A community perspective MATTER Stach, E., DeCost, B., Kusne, A., Hattrick-Simpers, J., Brown, K. A., Reyes, K. G., Schrier, J., Billinge, S., Buonassisi, T., Foster, I., Gomes, C. P., Gregoire, J. M., Mehta, A., Montoya, J., Olivetti, E., Park, C., Rotenberg, E., Saikin, S. K., Smullin, S., Stanev, V., Maruyama, B. 2021; 4 (9): 2702-2726

  View details for DOI 10.1016/j.matt.2021.06.036

  View details for Web of Science ID 000702820600006

• Dynamics and Hysteresis of Hydrogen Intercalation and Deintercalation in Palladium Electrodes: A Multimodal In Situ X-ray Diffraction, Coulometry, and Computational Study CHEMISTRY OF MATERIALS Landers, A. T., Peng, H., Koshy, D. M., Lee, S., Feaster, J. T., Lin, J. C., Beeman, J. W., Higgins, D., Yano, J., Drisdell, W. S., Davis, R. C., Bajdich, M., Abild-Pedersen, F., Mehta, A., Jaramillo, T. F., Hahn, C. 2021; 33 (15): 5872-5884

  View details for DOI 10.1021/acs.chemmater.1c00291

  View details for Web of Science ID 000685206200005

• Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion. Advanced materials (Deerfield Beach, Fla.) Muscher, P. K., Rehn, D. A., Sood, A., Lim, K., Luo, D., Shen, X., Zajac, M., Lu, F., Mehta, A., Li, Y., Wang, X., Reed, E. J., Chueh, W. C., Lindenberg, A. M. 2021: e2101875

  Abstract

  On-chip dynamic strain engineering requires efficient micro-actuators that can generate large in-plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (1V) and produce considerable strains (1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful "straintronic" devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe2 causes large anisotropic in-plane strain: 5% in one in-plane direction and 0.1% in the other. This efficient stretching of the 2D WTe2 layers contrasts to intercalation-induced strains in related materials which are predominantly in the out-of-plane direction. The unusual actuation of Lix WTe2 is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On-chip low-voltage (<0.2V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'-Li0.5- delta WTe2 phase, a uniaxial in-plane strain of 1.4% is achieved with a change of delta of only 0.075. This makes the in-plane chemical expansion coefficient of Td'-Li0.5-delta WTe2 far greater than of any other single-phase material, enabling fast and efficient planar electrochemical actuation.

  View details for DOI 10.1002/adma.202101875

  View details for PubMedID 34331368

• Cation and anion topotactic transformations in cobaltite thin films leading to Ruddlesden-Popper phases PHYSICAL REVIEW MATERIALS Chiu, I., Lee, M., Cheng, S., Zhang, S., Heki, L., Zhang, Z., Mohtashami, Y., Lapa, P. N., Feng, M., Shafer, P., N'Diaye, A. T., Mehta, A., Schuller, J. A., Galli, G., Ramanathan, S., Zhu, Y., Schuller, I. K., Takamura, Y. 2021; 5 (6)

  View details for DOI 10.1103/PhysRevMaterials.5.064416

  View details for Web of Science ID 000665792200006

• Emergent long-range magnetic order in ultrathin (111)-oriented LaNiO3 films NPJ QUANTUM MATERIALS Kane, M. M., Vailionis, A., Riddiford, L. J., Mehta, A., N'Diaye, A. T., Klewe, C., Shafer, P., Arenholz, E., Suzuki, Y. 2021; 6 (1)

  View details for DOI 10.1038/s41535-021-00345-2

  View details for Web of Science ID 000656948700001

• A refraction correction for buried interfaces applied to in situ grazing-incidence X-ray diffraction studies on Pd electrodes. Journal of synchrotron radiation Landers, A. T., Koshy, D. M., Lee, S. H., Drisdell, W. S., Davis, R. C., Hahn, C., Mehta, A., Jaramillo, T. F. 2021; 28 (Pt 3): 919–23

  Abstract

  In situ characterization of electrochemical systems can provide deep insights into the structure of electrodes under applied potential. Grazing-incidence X-ray diffraction (GIXRD) is a particularly valuable tool owing to its ability to characterize the near-surface structure of electrodes through a layer of electrolyte, which is of paramount importance in surface-mediated processes such as catalysis and adsorption. Corrections for the refraction that occurs as an X-ray passes through an interface have been derived for a vacuum-material interface. In this work, a more general form of the refraction correction was developed which can be applied to buried interfaces, including liquid-solid interfaces. The correction is largest at incidence angles near the critical angle for the interface and decreases at angles larger and smaller than the critical angle. Effective optical constants are also introduced which can be used to calculate the critical angle for total external reflection at the interface. This correction is applied to GIXRD measurements of an aqueous electrolyte-Pd interface, demonstrating that the correction allows for the comparison of GIXRD measurements at multiple incidence angles. This work improves quantitative analysis of d-spacing values from GIXRD measurements of liquid-solid systems, facilitating the connection between electrochemical behavior and structure under in situ conditions.

  View details for DOI 10.1107/S1600577521001557

  View details for PubMedID 33949999

• Phase stabilization and oxidation of a continuous composition spread multi-principal element (AlFeNiTiVZr)(1-x)Cr-x alloy JOURNAL OF ALLOYS AND COMPOUNDS Ruiz-Yi, B., Williams, T., Bunn, J., Ren, F., Al Hasan, N., Takeuchi, I., Hattrick-Simpers, J., Mehta, A. 2021; 861

  View details for DOI 10.1016/j.jallcom.2020.158565

  View details for Web of Science ID 000619199300102

• In Situ Characterization of Ferroelectric HfO₂ During Rapid Thermal Annealing PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS Narasimhan, V., McBriarty, M. E., Passarello, D., Adinolfi, V., Toney, M. F., Mehta, A., Littau, K. A. 2021; 15 (5)

  View details for DOI 10.1002/pssr.202000598

  View details for Web of Science ID 000615789600001

• Characterization data of an (AlFeNiTiVZr)1-xCrx multi-principal element alloy continuous composition spread library. Data in brief Ruiz-Yi, B., Williams, T., Bunn, J. K., Ren, F., Hasan, N. A., Takeuchi, I., Hattrick-Simpers, J., Mehta, A. 2021; 34: 106758

  Abstract

  The data provided in this article is related to the research article entitled "Phase stabilization and oxidation of a continuous composition spread multi-principal element (AlFeNiTiVZr)1-xCrx alloy" [1]. This data article describes the high-throughput synthesis and characterization processes of an (AlFeNiTiVZr)1-xCrx alloy system. Continuous composition spread (CCS) thin-film libraries were synthesized by co-depositing an AlFeNiTiVZr metal alloy target and Cr target via magnetron sputtering. Post-processing was performed on the sample libraries with a vacuum anneal at 873 K and an air anneal at 873 K. Compositional data was determined via WDS in order to verify parameters provided by an in-house sputter model. Crystallographic data was captured via synchrotron diffraction and diffractograms were compared as a function of the change in Cr concentration. These measurements were taken in order to observe phase behavior after oxidation throughout the composition library. Furthermore, vibrational spectrographic data is provided of the oxidized library to show surface speciation along the composition gradient of the alloy system. The structural and oxidative behavior of the (AlFeNiTiVZr)1-xCrx alloy can be analysed using the data provided in this article. Additionally, this characterization dataset can be utilized in machine learning algorithms for determining important features and parameters for future hypothesis generation of functional multi-principal element alloys (MPEAs).

  View details for DOI 10.1016/j.dib.2021.106758

  View details for PubMedID 33537375

• Identifying and Tuning the In Situ Oxygen-Rich Surface of Molybdenum Nitride Electrocatalysts for Oxygen Reduction ACS APPLIED ENERGY MATERIALS Stevens, M., Kreider, M. E., Patel, A. M., Wang, Z., Liu, Y., Gibbons, B. M., Statt, M. J., Ievlev, A., Sinclair, R., Mehta, A., Davis, R. C., Norskov, J. K., Gallo, A., King, L. A., Jaramillo, T. F. 2020; 3 (12): 12433–46

  View details for DOI 10.1021/acsaem.0c02423

  View details for Web of Science ID 000618839200099

• On-the-fly closed-loop materials discovery via Bayesian active learning. Nature communications Kusne, A. G., Yu, H., Wu, C., Zhang, H., Hattrick-Simpers, J., DeCost, B., Sarker, S., Oses, C., Toher, C., Curtarolo, S., Davydov, A. V., Agarwal, R., Bendersky, L. A., Li, M., Mehta, A., Takeuchi, I. 2020; 11 (1): 5966

  Abstract

  Active learning-the field of machine learning (ML) dedicated to optimal experiment design-has played a part in science as far back as the 18th century when Laplace used it to guide his discovery of celestial mechanics. In this work, we focus a closed-loop, active learning-driven autonomous system on another major challenge, the discovery of advanced materials against the exceedingly complex synthesis-processes-structure-property landscape. We demonstrate an autonomous materials discovery methodology for functional inorganic compounds which allow scientists to fail smarter, learn faster, and spend less resources in their studies, while simultaneously improving trust in scientific results and machine learning tools. This robot science enables science-over-the-network, reducing the economic impact of scientists being physically separated from their labs. The real-time closed-loop, autonomous system for materials exploration and optimization (CAMEO) is implemented at the synchrotron beamline to accelerate the interconnected tasks of phase mapping and property optimization, with each cycle taking seconds to minutes. We also demonstrate an embodiment of human-machine interaction, where human-in-the-loop is called to play a contributing role within each cycle. This work has resulted in the discovery of a novel epitaxial nanocomposite phase-change memory material.

  View details for DOI 10.1038/s41467-020-19597-w

  View details for PubMedID 33235197

• High-Throughput Characterization of (FexCo1-x)3O4 Thin-Film Composition Spreads. ACS combinatorial science Piotrowiak, T. H., Wang, X., Banko, L., Kumari, S., Sarker, S., Mehta, A., Ludwig, A. 2020

  Abstract

  Thin-film continuous composition spreads of Fe-Co-O were fabricated by reactive cosputtering from elemental Fe and Co targets in reactive Ar/O2 atmosphere using deposition temperatures ranging from 300 to 700 °C. Fused silica and platinized Si/SiO2 strips were used as substrates. Ti and Ta were investigated as adhesion layer for Pt and the fabrication of the Fe-Co-O films. The thin-film composition spreads were characterized by high-throughput electron-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and optical transmission spectroscopy. The Fe-content ranged from 28 to 72 at. %. The spinel phases Fe2CoO4 and FeCo2O4 could be synthesized and stabilized at all deposition temperatures with a continuous variation in spinel composition in between. The dependence of the film surface microstructure on the deposition temperature and the composition was mapped. Moreover, the band gap values, ranging from 2.41 eV for FeCo2O4 to 2.74 eV for Fe2CoO4, show a continuous variation with the composition.

  View details for DOI 10.1021/acscombsci.0c00126

  View details for PubMedID 33152234

• Exploring the First High-Entropy Thin Film Libraries: Composition Spread-Controlled Crystalline Structure. ACS combinatorial science Nguyen, T. X., Su, Y., Hattrick-Simpers, J., Joress, H., Nagata, T., Chang, K., Sarker, S., Mehta, A., Ting, J. 2020

  Abstract

  Thin films of two types of high-entropy oxides (HEOs) have been deposited on 76.2 mm Si wafers using combinatorial sputter deposition. In one type of the oxides, (MgZnMnCoNi)Ox, all the metals have a stable divalent oxidation state and similar cationic radii. In the second type of oxides, (CrFeMnCoNi)Ox, the metals are more diverse in the atomic radius and valence state, and have good solubility in their sub-binary and ternary oxide systems. The resulting HEO thin films were characterized using several high-throughput analytical techniques. The microstructure, composition, and electrical conductivity obtained on defined grid maps were obtained for the first time across large compositional ranges. The crystalline structure of the films was observed as a function of the metallic elements in the composition spreads, that is, the Mn and Zn in (MgZnMnCoNi)Ox and Mn and Ni in (CrFeMnCoNi)Ox. The (MgZnMnCoNi)Ox sample was observed to form two-phase structures, except single spinel structure was found in (MgZnMnCoNi)Ox over a range of Mn > 12 at. % and Zn < 44 at. %, while (CrFeMnCoNi)Ox was always observed to form two-phase structures. Composition-controlled crystalline structure is not only experimentally demonstrated but also supported by density function theory calculation.

  View details for DOI 10.1021/acscombsci.0c00159

  View details for PubMedID 33146510

• Controlling Magnetization Vector Depth Profiles of La_0.7Sr_0.3CoO₃/La_0.7Sr_0.3MnO₃ Exchange Spring Bilayers via Interface Reconstruction ACS APPLIED MATERIALS & INTERFACES Kane, A. M., Chiu, I., Ahlm, N. J., Chopdekar, R., N'Diaye, A. T., Arenholz, E., Mehta, A., Lauter, V., Takamura, Y. 2020; 12 (40): 45437-45443

  Abstract

  The La0.7Sr0.3CoO3-δ/La0.7Sr0.3MnO3-δ (LSCO/LSMO) bilayer system is an ideal perovskite oxide platform for investigating interface reconstruction and its effect on their magnetic properties. Previous studies have shown that LSCO can separate into magnetic sublayers, which possess distinct trends as the total LSCO thickness increases. In this study, we used polarized neutron reflectometry to quantify changes in the magnetic and chemical depth profiles, and it confirms the formation of ∼12 Å-thick interfacial LSCO and LSMO layers, characterized by a decreased nuclear scattering length density compared to the bulk of the layers. This decrease is attributed to the combined effects of oxygen vacancy formation and interfacial charge transfer, which lead to magnetically active Co2+ ions with ionic radii larger than the Co3+/Co4+ ions typically found in bulk LSCO or single-layer films. The interfacial magnetization values, as well as Co2+ ion and oxygen vacancy concentrations, depend strongly on the LSCO layer thickness. These results highlight the sensitive interplay of the cation valence states, oxygen vacancy concentration, and magnetization at interfaces in perovskite oxide multilayers, demonstrating the potential to tune their functional properties via careful design of their structure.

  View details for DOI 10.1021/acsami.0c09417

  View details for Web of Science ID 000579956100105

  View details for PubMedID 32852194

• Combinatorial Exploration and Mapping of Phase Transformation in a Ni-Ti-Co Thin Film Library. ACS combinatorial science Al Hasan, N. M., Hou, H., Gao, T., Counsell, J., Sarker, S., Thienhaus, S., Walton, E., Decker, P., Mehta, A., Ludwig, A., Takeuchi, I. 2020

  Abstract

  Combinatorial synthesis and high-throughput characterization of a Ni-Ti-Co thin film materials library are reported for exploration of reversible martensitic transformation. The library was prepared by magnetron co-sputtering, annealed in vacuum at 500 °C without atmospheric exposure, and evaluated for shape memory behavior as an indicator of transformation. Composition, structure, and transformation behavior of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and four-point probe temperature-dependent resistance (R(T)) measurements. A new, expanded composition space having phase transformation with low thermal hysteresis and Co > 10 at. % is found. Unsupervised machine learning methods of hierarchical clustering were employed to streamline data processing of the large XRD and XPS data sets. Through cluster analysis of XRD data, we identified and mapped the constituent structural phases. Composition-structure-property maps for the ternary system are made to correlate the functional properties to the local microstructure and composition of the Ni-Ti-Co thin film library.

  View details for DOI 10.1021/acscombsci.0c00097

  View details for PubMedID 32786322

• A High-Throughput Structural and Electrochemical Study of Metallic Glass Formation in Ni-Ti-Al ACS COMBINATORIAL SCIENCE Joress, H., DeCost, B. L., Sarker, S., Braun, T. M., Jilani, S., Smith, R., Ward, L., Laws, K. J., Mehta, A., Hattrick-Simpers, J. R. 2020; 22 (7): 330–38

  Abstract

  On the basis of a set of machine learning predictions of glass formation in the Ni-Ti-Al system, we have undertaken a high-throughput experimental study of that system. We utilized rapid synthesis followed by high-throughput structural and electrochemical characterization. Using this dual-modality approach, we are able to better classify the amorphous portion of the library, which we found to be the portion with a full width at half maximum (fwhm) of >0.42 Å-1 for the first sharp X-ray diffraction peak. Proper phase labeling is important for future machine learning efforts. We demonstrate that the fwhm and corrosion resistance are correlated but that, while chemistry still plays a role in corrosion resistance, a large fwhm, attributed to a glassy phase, is necessary for the highest corrosion resistance.

  View details for DOI 10.1021/acscombsci.9b00215

  View details for Web of Science ID 000607536400002

  View details for PubMedID 32496755

• Structural and photoelectrochemical properties in the thin film system Cu-Fe-V-O and its ternary subsystems Fe-V-O and Cu-V-O. The Journal of chemical physics Kumari, S., Junqueira, J. R., Sarker, S., Mehta, A., Schuhmann, W., Ludwig, A. 2020; 153 (1): 014707

  Abstract

  Thin-film material libraries in the ternary and quaternary metal oxide systems Fe-V-O, Cu-V-O, and Cu-Fe-V-O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu-Fe-V-O, the compositions (Fe61V39)Ox and (Cu52V48)Ox with promising photoactivity were identified from their ternary subsystems Fe-V-O and Cu-V-O, respectively. Two Cu-Fe-V-O material libraries with (Cu29-72Fe4-27V22-57)Ox and (Cu11-55Fe27-73V12-34)Ox composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (alpha-Cu3FeV6O26/FeVO4), II (Cu5V2O10/FeVO4/alpha-Cu3Fe4V6O26), III (Cu5V2O10), IV (Cu5V2O10/FeVO4, V (FeVO4/gamma-Cu2V2O7/alpha-Cu3Fe4V6O26), VI (beta-Cu2V2O7/alpha-Cu3Fe4V6O26/FeVO4), and VII (beta-Cu3Fe4V6O26/FeVO4). In the investigated composition range, two photoactive regions, (Cu53Fe7V40)Ox and (Cu45Fe21V34)Ox, were identified, exhibiting 103 muA/cm2 and 108 muA/cm2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu45Fe21V34)Ox comprises the dominant alpha-Cu3Fe4V6O24 phase and minor FeVO4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm.

  View details for DOI 10.1063/5.0009512

  View details for PubMedID 32640827

• Visualizing Energy Transfer at Buried Interfaces in Layered Materials Using Picosecond X-Rays ADVANCED FUNCTIONAL MATERIALS Nyby, C., Sood, A., Zalden, P., Gabourie, A. J., Muscher, P., Rhodes, D., Mannebach, E., Corbett, J., Mehta, A., Pop, E., Heinz, T. F., Lindenberg, A. M. 2020

  View details for DOI 10.1002/adfm.202002282

  View details for Web of Science ID 000544093300001

• Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni-Ti-Cu-V Quaternary Thin-Film Library ENGINEERING Al Hasan, N. M., Hou, H., Sarkar, S., Thienhaus, S., Mehta, A., Ludwig, A., Takeuchi, I. 2020; 6 (6): 637-643

  View details for DOI 10.1016/j.eng.2020.05.003

  View details for Web of Science ID 000545314200011

• Enhanced ferroelectricity in ultrathin films grown directly on silicon (vol 580, pg 478, 2020) NATURE Cheema, S. S., Kwon, D., Shanker, N., dos Reis, R., Hsu, S., Xiao, J., Zhang, H., Wagner, R., Datar, A., McCarter, M. R., Serrao, C. R., Yadav, A. K., Karbasian, G., Hsu, C., Tan, A. J., Wang, L., Thakare, V., Zhang, X., Mehta, A., Karapetrova, E., Chopdekar, R., Shafer, P., Arenholz, E., Hu, C., Proksch, R., Ramesh, R., Ciston, J., Salahuddin, S. 2020: E5

  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/s41586-020-2297-6

  View details for Web of Science ID 000531504100001

  View details for PubMedID 32433606

• High-throughput characterization of Ag-V-O nanostructured thin-film materials libraries for photoelectrochemical solar water splitting INTERNATIONAL JOURNAL OF HYDROGEN ENERGY Kumari, S., Helt, L., Junqueira, J. C., Kostka, A., Zhang, S., Sarker, S., Mehta, A., Scheu, C., Schuhmann, W., Ludwig, A. 2020; 45 (21): 12037–47

  View details for DOI 10.1016/j.ijhydene.2020.02.154

  View details for Web of Science ID 000524161700013

• Nitride or Oxynitride? Elucidating the Composition-Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction CHEMISTRY OF MATERIALS Kreider, M. E., Stevens, M., Liu, Y., Patel, A. M., Statt, M. J., Gibbons, B. M., Gallo, A., Ben-Naim, M., Mehta, A., Davis, R. C., Ievlev, A., Norskov, J. K., Sinclair, R., King, L. A., Jaramillo, T. F. 2020; 32 (7): 2946–60

  View details for DOI 10.1021/acs.chemmater.9b05212

  View details for Web of Science ID 000526394000025

• Enhanced ferroelectricity in ultrathin films grown directly on silicon. Nature Cheema, S. S., Kwon, D., Shanker, N., Dos Reis, R., Hsu, S., Xiao, J., Zhang, H., Wagner, R., Datar, A., McCarter, M. R., Serrao, C. R., Yadav, A. K., Karbasian, G., Hsu, C., Tan, A. J., Wang, L., Thakare, V., Zhang, X., Mehta, A., Karapetrova, E., Chopdekar, R. V., Shafer, P., Arenholz, E., Hu, C., Proksch, R., Ramesh, R., Ciston, J., Salahuddin, S. 2020; 580 (7804): 478–82

  Abstract

  Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality logic and nonvolatile memories1,2. As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides-the archetypal ferroelectric system3. Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes4. Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO2), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems-that is, from perovskite-derived complex oxides to fluorite-structure binary oxides-in which 'reverse' size effects counterintuitively stabilize polar symmetry in the ultrathin regime.

  View details for DOI 10.1038/s41586-020-2208-x

  View details for PubMedID 32322080

• High-Throughput Exploration of Lithium-Alloy Protection Layers for High-Performance Lithium-Metal Batteries ACS APPLIED ENERGY MATERIALS Manandhar, K., Ren, Y., Stasak, D., Hou, H., Kirsch, D., Sarker, S., Mehta, A., Sardar, S., Xiao, M., Weaver, J. L., Leon, C., Hart, G., Sunaoshi, T., Lemmon, J. P., Takeuchi, I. 2020; 3 (3): 2547-2555

  View details for DOI 10.1021/acsaem.9b02252

  View details for Web of Science ID 000526598300055

• Phase transitions and magnetic domain coexistence in Nd_0.5Sr_0.5MnO₃ thin films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Chiu, I., Kane, A. M., Chopdekar, R. V., Lyu, P., Mehta, A., Rouleau, C. M., N'Diaye, A. T., Arenholz, E., Takamura, Y. 2020; 498

  View details for DOI 10.1016/j.jmmm.2019.166116

  View details for Web of Science ID 000504845300094

• In Situ X-Ray Absorption Spectroscopy Disentangles the Roles of Copper and Silver in a Bimetallic Catalyst for the Oxygen Reduction Reaction CHEMISTRY OF MATERIALS Gibbons, B. M., Wette, M., Stevens, M., Davis, R. C., Siahrostami, S., Kreider, M., Mehta, A., Higgins, D. C., Clemens, B. M., Jaramillo, T. F. 2020; 32 (5): 1819–27

  View details for DOI 10.1021/acs.chemmater.9b03963

  View details for Web of Science ID 000519337600008

• Metal-promoted Mo6S8 clusters: a platform for probing ensemble effects on the electrochemical conversion of CO2 and CO to methanol MATERIALS HORIZONS Perryman, J. T., Ortiz-Rodriguez, J. C., Jude, J. W., Hyler, F. P., Davis, R. C., Mehta, A., Kulkarni, A. R., Patridge, C. J., Velazquez, J. M. 2020; 7 (1): 193–202

  View details for DOI 10.1039/c9mh00745h

  View details for Web of Science ID 000518381300020

• Development of new Mg-Zn-Sr alloys for medical purpose Sulikova, M., Molcanova, Z., Ballokova, B., Durisin, J., Martinkova, S., Varcholova, D., Michalik, S., Tang-Kong, R., Ward, L., Mehta, A., Sulova, K., Fejercak, M., Lachova, A., Dzunda, R., Saksl, K. INDERSCIENCE ENTERPRISES LTD. 2020: 573–82

  View details for DOI 10.1504/IJNT.2020.111327

  View details for Web of Science ID 000595645700008

• Oxidation State and Surface Reconstruction of Cu under CO2 Reduction Conditions from In Situ X-ray Characterization. Journal of the American Chemical Society Lee, S. H., Lin, J. C., Farmand, M. n., Landers, A. T., Feaster, J. T., Avilés Acosta, J. E., Beeman, J. W., Ye, Y. n., Yano, J. n., Mehta, A. n., Davis, R. C., Jaramillo, T. F., Hahn, C. n., Drisdell, W. S. 2020

  Abstract

  The electrochemical CO2 reduction reaction (CO2RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO2RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO2RR, and the catalyst maintains the metallic state across the potentials relevant to the CO2RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO2. Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO2RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis.

  View details for DOI 10.1021/jacs.0c10017

  View details for PubMedID 33382947

• Combinatorial Tuning of Structural and Optoelectronic Properties in CuXZn1-XS MATTER Woods-Robinson, R., Han, Y., Mangum, J. S., Melamed, C. L., Gorman, B. P., Mehta, A., Persson, K. A., Zakutayev, A. 2019; 1 (4): 862-880

  View details for DOI 10.1016/j.matt.2019.06019

  View details for Web of Science ID 000519847300012

• Crystal Phase Distribution and Ferroelectricity in Ultrathin HfO2-ZrO2 Bilayers PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS McBriarty, M. E., Narasimhan, V. K., Weeks, S. L., Pal, A., Fang, H., Petach, T. A., Mehta, A., Davis, R. C., Barabash, S., Littau, K. A. 2019

  View details for DOI 10.1002/pssb.201900285

  View details for Web of Science ID 000486269200001

• Materials science in the artificial intelligence age: high-throughput library generation, machine learning, and a pathway from correlations to the underpinning physics MRS COMMUNICATIONS Vasudevan, R. K., Choudhary, K., Mehta, A., Smith, R., Kusne, G., Tavazza, F., Vlcek, L., Ziatdinov, M., Kalinin, S. V., Hattrick-Simpers, J. 2019; 9 (3): 821–38

  View details for DOI 10.1557/mrc.2019.95

  View details for Web of Science ID 000488237800004

• Controlling shape memory effects in NiTi thin films grown on Ru seed layer SENSORS AND ACTUATORS A-PHYSICAL Ainslie, K., Knick, C., Smith, G., Li, J., Troxel, C., Mehta, A., Kukreja, R. 2019; 294: 133–39

  View details for DOI 10.1016/j.sna.2019.04.047

  View details for Web of Science ID 000472988800015

• An Inter-Laboratory Study of Zn-Sn-Ti-O Thin Films using High-Throughput Experimental Methods ACS COMBINATORIAL SCIENCE Hattrick-Simpers, J. R., Zakutayev, A., Barron, S. C., Trautt, Z. T., Nam Nguyen, Choudhary, K., DeCost, B., Phillips, C., Kusne, A., Yi, F., Mehta, A., Takeuchi, I., Perkins, J. D., Green, M. L. 2019; 21 (5): 350-361

  Abstract

  High-throughput experimental (HTE) techniques are an increasingly important way to accelerate the rate of materials research and development for many technological applications. However, there are very few publications on the reproducibility of the HTE results obtained across different laboratories for the same materials system, and on the associated sample and data exchange standards. Here, we report a comparative study of Zn-Sn-Ti-O thin films materials using high-throughput experimental methods at National Institute of Standards and Technology (NIST) and National Renewable Energy Laboratory (NREL). The thin film sample libraries were synthesized by combinatorial physical vapor deposition (cosputtering and pulsed laser deposition) and characterized by spatially resolved techniques for composition, structure, thickness, optical, and electrical properties. The results of this study indicate that all these measurement techniques performed at two different laboratories show excellent qualitative agreement. The quantitative similarities and differences vary by measurement type, with 95% confidence interval of 0.1-0.2 eV for the band gap, 24-29 nm for film thickness, and 0.08 to 0.37 orders of magnitude for sheet resistance. Overall, this work serves as a case study for the feasibility of a High-Throughput Experimental Materials Collaboratory (HTE-MC) by demonstrating the exchange of high-throughput sample libraries, workflows, and data.

  View details for DOI 10.1021/acscombsci.8b00158

  View details for Web of Science ID 000468120600002

  View details for PubMedID 30888788

• X-ray absorption spectroscopy study of the electronic structure and local coordination of 1st row transition metal-promoted Chevrel-phase sulfides JOURNAL OF COORDINATION CHEMISTRY Perryman, J. T., Hyler, F. P., Ortiz-Rodriguez, J. C., Mehta, A., Kulkarni, A. R., Velazquez, J. M. 2019; 72 (8): 1322–35

  View details for DOI 10.1080/00958972.2019.1613532

  View details for Web of Science ID 000475969300010

• Observing hydrogen intercalation into palladium thin films using in situ grazing incidence x-ray diffraction and x-ray reflectivity Landers, A., Feaster, J., Brown, K., Lin, J., Farmand, M., Fackler, S., Nishimura, Y., Beeman, J., Bajdich, M., Higgins, D., Yano, J., Drisdell, W., Davis, R., Hahn, C., Mehta, A., Jaramillo, T. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478860506048

• Absence of Oxidized Phases in Cu under CO Reduction Conditions ACS ENERGY LETTERS Scott, S. B., Hogg, T. V., Landers, A. T., Maagaard, T., Bertheussen, E., Lin, J. C., Davis, R. C., Beeman, J. W., Higgins, D., Drisdell, W. S., Hahn, C., Mehta, A., Seger, B., Jaramillo, T. F., Chorkendorff, I. 2019; 4 (3): 803–4

  View details for DOI 10.1021/acsenergylett.9b00172

  View details for Web of Science ID 000461271600027

• Phase selection motifs in High Entropy Alloys revealed through combinatorial methods: Large atomic size difference favors BCC over FCC ACTA MATERIALIA Kube, S., Sohn, S., Uhl, D., Datye, A., Mehta, A., Schroers, J. 2019; 166: 677-686

  View details for DOI 10.1016/j.actamat.2019.01.023

  View details for Web of Science ID 000459358200059

• Electrochemical flow cell enabling operando probing of electrocatalyst surfaces by X-ray spectroscopy and diffraction. Physical chemistry chemical physics : PCCP Farmand, M., Landers, A. T., Lin, J. C., Feaster, J. T., Beeman, J. W., Ye, Y., Clark, E. L., Higgins, D., Yano, J., Davis, R. C., Mehta, A., Jaramillo, T. F., Hahn, C., Drisdell, W. S. 2019

  Abstract

  The rational improvement of current and developing electrochemical technologies requires atomistic understanding of electrode-electrolyte interfaces. However, examining these interfaces under operando conditions, where performance is typically evaluated and benchmarked, remains challenging, as it necessitates incorporating an operando probe during full electrochemical operation. In this study, we describe a custom electrochemical flow cell that enables near-surface-sensitive operando investigation of planar thin-film catalysts at significant hydrogen evolution reaction (HER) rates (in excess of -100 mA cm-2) using grazing incidence X-ray methods. Grazing-incidence X-ray spectroscopy and diffraction were implemented on the same sample under identical HER conditions, demonstrating how the combined measurements track changing redox chemistry and structure of Cu thin-film catalyst surfaces as a function of electrochemical conditions. The coupling of these methods with improved mass transport and hydrodynamic control establishes a new paradigm for operando measurement design, enabling unique insights into the key fundamental processes occurring at the catalyst-electrolyte interface.

  View details for DOI 10.1039/c8cp07423b

  View details for PubMedID 30785434

• Decoupling exchange bias and coercivity enhancement in a perovskite oxide exchange spring bilayer PHYSICAL REVIEW MATERIALS Kane, A. M., Chopdekar, R. V., N'Diaye, A. T., Scholl, A., Arenholz, E., Mehta, A., Takamura, Y. 2019; 3 (1)

  View details for DOI 10.1103/PhysRevMaterials.3.014413

  View details for Web of Science ID 000456796500002

• Garnet Electrolyte Surface Degradation and Recovery ACS APPLIED ENERGY MATERIALS Cheng, L., Liu, M., Mehta, A., Xin, H., Lin, F., Persson, K., Chen, G., Crumlin, E. J., Doeff, M. 2018; 1 (12): 7244-+

  View details for DOI 10.1021/acsaem.8b01723

  View details for Web of Science ID 000458706800070

• Ionic tuning of cobaltites at the nanoscale PHYSICAL REVIEW MATERIALS Gilbert, D. A., Grutter, A. J., Murray, P. D., Chopdekar, R. V., Kane, A. M., Ionin, A. L., Lee, M. S., Spurgeon, S. R., Kirby, B. J., Maranville, B. B., N'Diaye, A. T., Mehta, A., Arenholz, E., Liu, K., Takamura, Y., Borchers, J. A. 2018; 2 (10)

  View details for DOI 10.1103/PhysRevMaterials.2.104402

  View details for Web of Science ID 000446395500003

• Can machine learning identify the next high-temperature superconductor? Examining extrapolation performance for materials discovery MOLECULAR SYSTEMS DESIGN & ENGINEERING Meredig, B., Antono, E., Church, C., Hutchinson, M., Ling, J., Paradiso, S., Blaiszik, B., Foster, I., Gibbons, B., Hattrick-Simpers, J., Mehta, A., Ward, L. 2018; 3 (5): 819–25

  View details for DOI 10.1039/c8me00012c

  View details for Web of Science ID 000448419000009

• Surface Orientation Dependent Water Dissociation on Rutile Ruthenium Dioxide JOURNAL OF PHYSICAL CHEMISTRY C Rao, R. R., Kolb, M. J., Hwang, J., Pedersen, A., Mehta, A., You, H., Stoerzinger, K. A., Feng, Z., Zhou, H., Bluhm, H., Giordano, L., Stephens, I. L., Shao-Horn, Y. 2018; 122 (31): 17802–11

  View details for DOI 10.1021/acs.jpcc.8b04284

  View details for Web of Science ID 000441484600024

• Xi-cam: a versatile interface for data visualization and analysis. Journal of synchrotron radiation Pandolfi, R. J., Allan, D. B., Arenholz, E., Barroso-Luque, L., Campbell, S. I., Caswell, T. A., Blair, A., De Carlo, F., Fackler, S., Fournier, A. P., Freychet, G., Fukuto, M., Gursoy, D., Jiang, Z., Krishnan, H., Kumar, D., Kline, R. J., Li, R., Liman, C., Marchesini, S., Mehta, A., N'Diaye, A. T., Parkinson, D. Y., Parks, H., Pellouchoud, L. A., Perciano, T., Ren, F., Sahoo, S., Strzalka, J., Sunday, D., Tassone, C. J., Ushizima, D., Venkatakrishnan, S., Yager, K. G., Zwart, P., Sethian, J. A., Hexemer, A. 2018; 25 (Pt 4): 1261–70

  Abstract

  Xi-cam is an extensible platform for data management, analysis and visualization. Xi-cam aims to provide a flexible and extensible approach to synchrotron data treatment as a solution to rising demands for high-volume/high-throughput processing pipelines. The core of Xi-cam is an extensible plugin-based graphical user interface platform which provides users with an interactive interface to processing algorithms. Plugins are available for SAXS/WAXS/GISAXS/GIWAXS, tomography and NEXAFS data. With Xi-cam's `advanced' mode, data processing steps are designed as a graph-based workflow, which can be executed live, locally or remotely. Remote execution utilizes high-performance computing or de-localized resources, allowing for the effective reduction of high-throughput data. Xi-cam's plugin-based architecture targets cross-facility and cross-technique collaborative development, in support of multi-modal analysis. Xi-cam is open-source and cross-platform, and available for download on GitHub.

  View details for DOI 10.1107/S1600577518005787

  View details for PubMedID 29979189

• Copper Silver Thin Films with Metastable Miscibility for Oxygen Reduction Electrocatalysis in Alkaline Electrolytes ACS APPLIED ENERGY MATERIALS Higgins, D., Wette, M., Gibbons, B. M., Siahrostami, S., Hahn, C., Escudero-Escribano, M., Garcia-Melchor, M., Ulissi, Z., Davis, R. C., Mehta, A., Clemens, B. M., Norskov, J. K., Jaramillo, T. F. 2018; 1 (5): 1990–99

  View details for DOI 10.1021/acsaem.8b00090

  View details for Web of Science ID 000458705500027

• Accelerated discovery of metallic glasses through iteration of machine learning and high-throughput experiments SCIENCE ADVANCES Ren, F., Ward, L., Williams, T., Laws, K. J., Wolverton, C., Hattrick-Simpers, J., Mehta, A. 2018; 4 (4): eaaq1566

  Abstract

  With more than a hundred elements in the periodic table, a large number of potential new materials exist to address the technological and societal challenges we face today; however, without some guidance, searching through this vast combinatorial space is frustratingly slow and expensive, especially for materials strongly influenced by processing. We train a machine learning (ML) model on previously reported observations, parameters from physiochemical theories, and make it synthesis method-dependent to guide high-throughput (HiTp) experiments to find a new system of metallic glasses in the Co-V-Zr ternary. Experimental observations are in good agreement with the predictions of the model, but there are quantitative discrepancies in the precise compositions predicted. We use these discrepancies to retrain the ML model. The refined model has significantly improved accuracy not only for the Co-V-Zr system but also across all other available validation data. We then use the refined model to guide the discovery of metallic glasses in two additional previously unreported ternaries. Although our approach of iterative use of ML and HiTp experiments has guided us to rapid discovery of three new glass-forming systems, it has also provided us with a quantitatively accurate, synthesis method-sensitive predictor for metallic glasses that improves performance with use and thus promises to greatly accelerate discovery of many new metallic glasses. We believe that this discovery paradigm is applicable to a wider range of materials and should prove equally powerful for other materials and properties that are synthesis path-dependent and that current physiochemical theories find challenging to predict.

  View details for DOI 10.1126/sciadv.aaq1566

  View details for Web of Science ID 000431374900043

  View details for PubMedID 29662953

  View details for PubMedCentralID PMC5898831

• Nanoparticles via vapor phase condensation for energy applications Clemens, B., Gibbons, B., Wetter, M., Higgins, D., Jaramillo, T., Baker, J., Bent, S., Mehta, A., Davis, R. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000435537706021

• Evidence that abnormal grain growth precedes fatigue crack initiation in nanocrystalline Ni-Fe SCRIPTA MATERIALIA Furnish, T. A., Bufford, D. C., Ren, F., Mehta, A., Hattar, K., Boyce, B. L. 2018; 143: 15–19

  View details for DOI 10.1016/j.scriptamat.2017.08.047

  View details for Web of Science ID 000413609500004

• Engineered superlattices with crossover from decoupled to synthetic ferromagnetic behavior JOURNAL OF PHYSICS-CONDENSED MATTER Chopdekar, R. V., Malik, V. K., Kane, A. M., Mehta, A., Arenholz, E., Takamura, Y. 2018; 30 (1): 015805

  Abstract

  The extent of interfacial charge transfer and the resulting impact on magnetic interactions were investigated as a function of sublayer thickness in La0.7Sr0.3MnO3/La0.7Sr0.3CoO3 ferromagnetic superlattices. Element-specific soft x-ray magnetic spectroscopy reveals that the electronic structure is altered within 5-6 unit cells of the chemical interface, and can lead to a synthetic ferromagnet with strong magnetic coupling between the sublayers. The saturation magnetization and coercivity depends sensitively on the sublayer thickness due to the length scale of this interfacial effect. For larger sublayer thicknesses, the La0.7Sr0.3MnO3 and La0.7Sr0.3CoO3 sublayers are magnetically decoupled, displaying two independent magnetic transitions with little sublayer thickness dependence. These results demonstrate how interfacial phenomena at perovskite oxide interfaces can be used to tailor their functional properties at the atomic scale.

  View details for DOI 10.1088/1361-648X/aa9b13

  View details for Web of Science ID 000423884100018

  View details for PubMedID 29144279

• The Complexity of the CaF₂:Yb System: A Huge, Reversible, X-ray-Induced Valence Reduction JOURNAL OF PHYSICAL CHEMISTRY C MacKeen, C., Bridges, F., Seijo, L., Barandiaran, Z., Kozina, M., Mehta, A., Reid, M. F., Wells, J. R. 2017; 121 (51): 28435-28442

  View details for DOI 10.1021/acs.jpcc.7b09161

  View details for Web of Science ID 000419263500025

• Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides. Nature communications Gent, W. E., Lim, K., Liang, Y., Li, Q., Barnes, T., Ahn, S. J., Stone, K. H., McIntire, M., Hong, J., Song, J. H., Li, Y., Mehta, A., Ermon, S., Tyliszczak, T., Kilcoyne, D., Vine, D., Park, J. H., Doo, S. K., Toney, M. F., Yang, W., Prendergast, D., Chueh, W. C. 2017; 8 (1): 2091

  Abstract

  Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li1.17-x Ni0.21Co0.08Mn0.54O2, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

  View details for DOI 10.1038/s41467-017-02041-x

  View details for PubMedID 29233965

  View details for PubMedCentralID PMC5727078

• Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides NATURE COMMUNICATIONS Gent, W. E., Lim, K., Liang, Y., Li, Q., Barnes, T., Ahn, S., Stone, K. H., McIntire, M., Hong, J., Song, J., Li, Y., Mehta, A., Ermon, S., Tyliszczak, T., Kilcoyne, D., Vine, D., Park, J., Doo, S., Toney, M. F., Yang, W., Prendergast, D., Chueh, W. C. 2017; 8

  View details for DOI 10.1038/s41467-017-02041-x

  View details for Web of Science ID 000417702300042

• Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution ENERGY & ENVIRONMENTAL SCIENCE Rao, R. R., Kolb, M. J., Halck, N., Pedersen, A., Mehta, A., You, H., Stoerzinger, K. A., Feng, Z., Hansen, H. A., Zhou, H., Giordano, L., Rossmeisl, J., Vegge, T., Chorkendorff, I., Stephens, I. L., Shao-Horn, Y. 2017; 10 (12): 2626–37

  View details for DOI 10.1039/c7ee02307c

  View details for Web of Science ID 000417255900015

• Finding a Needle in the Haystack: Identification of Functionally Important Minority Phases in an Operating Battery NANO LETTERS Zhang, K., Ren, F., Wang, X., Hu, E., Xu, Y., Yang, X., Li, H., Chen, L., Pianetta, P., Mehta, A., Yu, X., Liu, Y. 2017; 17 (12): 7782–88

  View details for DOI 10.1021/acs.nanolett.7b03985

  View details for Web of Science ID 000418393300084

• Dynamic Optical Tuning of Interlayer Interactions in the Transition Metal Dichalcogenides NANO LETTERS Mannebach, E. M., Nyby, C., Ernst, F., Zhou, Y., Tolsma, J., Li, Y., Sher, M., Tung, I., Zhou, H., Zhang, Q., Seyler, K. L., Clark, G., Lin, Y., Zhu, D., Glownia, J. M., Kozina, M. E., Song, S., Nelson, S., Mehta, A., Yu, Y., Pant, A., Aslan, O., Raja, A., Guo, Y., DiChiara, A., Mao, W., Cao, L., Tongay, S., Sun, J., Singh, D. J., Heinz, T. F., Xu, X., MacDonald, A. H., Reed, E., Wen, H., Lindenberg, A. M. 2017; 17 (12): 7761-7766

  View details for DOI 10.1021/acs.nanolett.7b03955

  View details for Web of Science ID 000418393300081

• On-the-fly segmentation approaches for x-ray diffraction datasets for metallic glasses MRS COMMUNICATIONS Ren, F., Williams, T., Hattrick-Simpers, J., Mehta, A. 2017; 7 (3): 613-620

  View details for DOI 10.1557/mrc.2017.76

  View details for Web of Science ID 000412602400034

• Multimodal x-ray characterization of solar fuels catalysts under operation Farmand, M., Feaster, J., Davis, R., Fackler, S., Landers, A., Lin, J., Hahn, C., Jaramillo, T., Yano, J., Mehta, A., Drisdell, W. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000429525602065

• Monitoring Deformation in Graphene Through Hyperspectral Synchrotron Spectroscopy to Inform Fabrication JOURNAL OF PHYSICAL CHEMISTRY C Winter, A., Rojas, W. Y., Williams, A. D., Kim, S. S., Ouchen, F., Fischer, D. A., Weiland, C., Principe, E., Banerjee, S., Huynh, C., Naik, R. R., Liu, Y., Mehta, A., Grote, J., Prendergast, D., Campo, E. M. 2017; 121 (29): 15653–64

  View details for DOI 10.1021/acs.jpcc.7b01376

  View details for Web of Science ID 000406726200019

• Evidence That the Anomalous Emission from CaF₂:Yb<SUP>2+</SUP> Is Not Described by the Impurity Trapped Exciton Model JOURNAL OF PHYSICAL CHEMISTRY LETTERS MacKeen, C., Bridges, F., Kozina, M., Mehta, A., Reid, M. F., Wells, J. R., Barandiaran, Z. 2017; 8 (14): 3313-3316

  Abstract

  Yb-substituted CaF2 exhibits an anomalous red-shifted luminescence after UV excitation, attributed to the relaxation of impurity trapped excitons (ITE). CaF2:Yb is the archetype system for this model, in which the Yb2+ ions can be excited into a long-lived (ms) exciton state. Upon de-excitation, the emission intensity should be proportional to the Yb2+ concentration, but that could not be checked when this model was first proposed. Using the X-ray absorption near edge structure (XANES) technique, we determine the fractions of Yb2+ and Yb3+ for low Yb concentrations, 0.01% to 0.1%, and thus determine the net concentration of Yb2+. A comparison with luminescence data shows that the intensity is not proportional to the Yb2+ concentration, and only a fraction of Yb2+ ions contributes to the anomalous luminescence. This is inconsistent with the ITE model and illustrates the importance of checking the dependence of the emission intensity on the Yb2+ concentration.

  View details for DOI 10.1021/acs.jpclett.7b01103

  View details for Web of Science ID 000406358000024

  View details for PubMedID 28677980

• Enhanced lithium ion transport in garnet-type solid state electrolytes JOURNAL OF ELECTROCERAMICS Cheng, L., Hou, H., Lux, S., Kostecki, R., Davis, R., Zorba, V., Mehta, A., Doeff, M. 2017; 38 (2-4): 168–75

  View details for DOI 10.1007/s10832-017-0080-3

  View details for Web of Science ID 000415362700005

• On-the-Fly Data Assessment for High-Throughput X-ray Diffraction Measurements. ACS combinatorial science Ren, F., Pandolfi, R., van Campen, D., Hexemer, A., Mehta, A. 2017

  Abstract

  Investment in brighter sources and larger and faster detectors has accelerated the speed of data acquisition at national user facilities. The accelerated data acquisition offers many opportunities for the discovery of new materials, but it also presents a daunting challenge. The rate of data acquisition far exceeds the current speed of data quality assessment, resulting in less than optimal data and data coverage, which in extreme cases forces recollection of data. Herein, we show how this challenge can be addressed through the development of an approach that makes routine data assessment automatic and instantaneous. By extracting and visualizing customized attributes in real time, data quality and coverage, as well as other scientifically relevant information contained in large data sets, is highlighted. Deployment of such an approach not only improves the quality of data but also helps optimize the usage of expensive characterization resources by prioritizing measurements of the highest scientific impact. We anticipate our approach will become a starting point for a sophisticated decision-tree that optimizes data quality and maximizes scientific content in real time through automation. With these efforts to integrate more automation in data collection and analysis, we can truly take advantage of the accelerating speed of data acquisition.

  View details for DOI 10.1021/acscombsci.7b00015

  View details for PubMedID 28463477

• Crystal truncation rods from miscut surfaces PHYSICAL REVIEW B Petach, T. A., Mehta, A., Toney, M. F., Goldhaber-Gordon, D. 2017; 95 (18)

  View details for DOI 10.1103/PhysRevB.95.184104

  View details for Web of Science ID 000401227800003

• Operando electrochemical grazing incidence x-ray absorption and diffraction for the CO2 reduction reaction Feaster, J., Farmand, M., Lin, J., Landers, A., Fackler, S., Davis, R., Mehta, A., Yano, J., Jaramillo, T., Drisdell, W. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430568502328

• Combinatorial study of Fe-Co-V hard magnetic thin films SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Fackler, S. W., Alexandrakis, V., Koenig, D., Kusne, A., Gao, T., Kramer, M. J., Stasak, D., Lopez, K., Zayac, B., Mehta, A., Ludwig, A., Takeuchi, I. 2017; 18 (1): 231–38

  Abstract

  Thin film libraries of Fe-Co-V were fabricated by combinatorial sputtering to study magnetic and structural properties over wide ranges of composition and thickness by high-throughput methods: synchrotron X-ray diffraction, magnetometry, composition, and thickness were measured across the Fe-Co-V libraries. In-plane magnetic hysteresis loops were shown to have a coercive field of 23.9 kA m-1 (300 G) and magnetization of 1000 kA m-1. The out-of-plane direction revealed enhanced coercive fields of 207 kA m-1 (2.6 kG) which was attributed to the shape anisotropy of column grains observed with electron microscopy. Angular dependence of the switching field showed that the magnetization reversal mechanism is governed by 180° domain wall pinning. In the thickness-dependent combinatorial study, co-sputtered composition spreads had a thickness ranging from 50 to 500 nm and (Fe70Co30)100-xVx compositions of x = 2-80. Comparison of high-throughput magneto-optical Kerr effect and traditional vibrating sample magnetometer measurements show agreement of trends in coercive fields across large composition and thickness regions.

  View details for PubMedID 28458744

  View details for PubMedCentralID PMC5402764

• Dynamic Optical Tuning of Interlayer Interactions in the Transition Metal Dichalcogenides. Nano letters Mannebach, E. M., Nyby, C. n., Ernst, F. n., Zhou, Y. n., Tolsma, J. n., Li, Y. n., Sher, M. J., Tung, I. C., Zhou, H. n., Zhang, Q. n., Seyler, K. L., Clark, G. n., Lin, Y. n., Zhu, D. n., Glownia, J. M., Kozina, M. E., Song, S. n., Nelson, S. n., Mehta, A. n., Yu, Y. n., Pant, A. n., Aslan, O. B., Raja, A. n., Guo, Y. n., DiChiara, A. n., Mao, W. n., Cao, L. n., Tongay, S. n., Sun, J. n., Singh, D. J., Heinz, T. F., Xu, X. n., MacDonald, A. H., Reed, E. n., Wen, H. n., Lindenberg, A. M. 2017; 17 (12): 7761–66

  Abstract

  Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation in the TMDCs leads to an unexpected large-amplitude, ultrafast compressive force between the two-dimensional layers, as probed by in situ measurements of the atomic layer spacing at femtosecond time resolution. We show that this compressive response arises from a dynamic modulation of the interlayer van der Waals interaction and that this represents the dominant light-induced stress at low excitation densities. A simple analytic model predicts the magnitude and carrier density dependence of the measured strains. This work establishes a new method for dynamic, nonequilibrium tuning of correlation-driven dispersive interactions and of the optomechanical functionality of TMDC quasi-two-dimensional materials.

  View details for PubMedID 29119791

• Understanding the Degradation Mechanism of Lithium Nickel Oxide Cathodes for Li-Ion Batteries ACS APPLIED MATERIALS & INTERFACES Xu, J., Hu, E., Nordlund, D., Mehta, A., Ehrlich, S. N., Yang, X., Tong, W. 2016; 8 (46): 31677–83

  Abstract

  The phase transition, charge compensation, and local chemical environment of Ni in LiNiO2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge-discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surface over the extended cycles. The degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO2.

  View details for DOI 10.1021/acsami.6b11111

  View details for Web of Science ID 000388913900023

  View details for PubMedID 27802012

• High Throughput Light Absorber Discovery, Part 2: Establishing Structure-Band Gap Energy Relationships ACS COMBINATORIAL SCIENCE Suram, S. K., Newhouse, P. F., Zhou, L., Van Campen, D. G., Mehta, A., Gregoire, J. M. 2016; 18 (11): 682-688

  Abstract

  Combinatorial materials science strategies have accelerated materials development in a variety of fields, and we extend these strategies to enable structure-property mapping for light absorber materials, particularly in high order composition spaces. High throughput optical spectroscopy and synchrotron X-ray diffraction are combined to identify the optical properties of Bi-V-Fe oxides, leading to the identification of Bi4V1.5Fe0.5O10.5 as a light absorber with direct band gap near 2.7 eV. The strategic combination of experimental and data analysis techniques includes automated Tauc analysis to estimate band gap energies from the high throughput spectroscopy data, providing an automated platform for identifying new optical materials.

  View details for DOI 10.1021/acscombsci.6b00054

  View details for Web of Science ID 000388155800004

  View details for PubMedID 27662502

• Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures APPLIED PHYSICS LETTERS Li, B., Chopdekar, R. V., N'Diaye, A. T., Mehta, A., Byers, J., Browning, N. D., Arenholz, E., Takamura, Y. 2016; 109 (15)

  View details for DOI 10.1063/1.4964407

  View details for Web of Science ID 000386534800028

• PtxGd alloy formation on Pt(111): Preparation and structural characterization SURFACE SCIENCE Ulrikkeholm, E. T., Pedersen, A. F., Vej-Hansen, U. G., Escudero-Escribano, M., Stephens, I. E., Friebel, D., Mehta, A., Schiotz, J., Feidenhansl, R. K., Nilsson, A., Chorkendorff, I. 2016; 652: 114-122

  View details for DOI 10.1016/j.susc.2016.02.009

  View details for Web of Science ID 000380600700017

• Unsupervised Data Mining in nanoscale X-ray Spectro-Microscopic Study of NdFeB Magnet SCIENTIFIC REPORTS Duan, X., Yang, F., Antono, E., Yang, W., Pianetta, P., Ermon, S., Mehta, A., Liu, Y. 2016; 6

  Abstract

  Novel developments in X-ray based spectro-microscopic characterization techniques have increased the rate of acquisition of spatially resolved spectroscopic data by several orders of magnitude over what was possible a few years ago. This accelerated data acquisition, with high spatial resolution at nanoscale and sensitivity to subtle differences in chemistry and atomic structure, provides a unique opportunity to investigate hierarchically complex and structurally heterogeneous systems found in functional devices and materials systems. However, handling and analyzing the large volume data generated poses significant challenges. Here we apply an unsupervised data-mining algorithm known as DBSCAN to study a rare-earth element based permanent magnet material, Nd2Fe14B. We are able to reduce a large spectro-microscopic dataset of over 300,000 spectra to 3, preserving much of the underlying information. Scientists can easily and quickly analyze in detail three characteristic spectra. Our approach can rapidly provide a concise representation of a large and complex dataset to materials scientists and chemists. For example, it shows that the surface of common Nd2Fe14B magnet is chemically and structurally very different from the bulk, suggesting a possible surface alteration effect possibly due to the corrosion, which could affect the material's overall properties.

  View details for DOI 10.1038/srep34406

  View details for Web of Science ID 000384188300001

  View details for PubMedID 27680388

  View details for PubMedCentralID PMC5041149

• The Different Roles of Entropy and Solubility in High Entropy Alloy Stability ACS COMBINATORIAL SCIENCE Ruiz-Yi, B., Bunn, J., Stasak, D., Mehta, A., Besser, M., Kramer, M. J., Takeuchi, I., Hattrick-Simpers, J. 2016; 18 (9): 596-603

  Abstract

  Multiprincipal element high entropy alloys stabilized as a single alloy phase represent a new material system with promising properties, such as high corrosion and creep resistance, sluggish diffusion, and high temperature tensile strength. However, the mechanism of stabilization to form single phase alloys is controversial. Early studies hypothesized that a large entropy of mixing was responsible for stabilizing the single phase; more recent work has proposed that the single-phase solid solution is the result of mutual solubility of the principal elements. Here, we demonstrate the first self-consistent study of the relative importance of these two proposed mechanisms. In situ high-throughput synchrotron diffraction studies were used to monitor the stability of the single phase alloy in thin-film (Al1-x-yCuxMoy)FeNiTiVZr composition spread samples. Our results indicate that a metastable solid solution can be captured via the rapid quenching typical of physical vapor deposition processes, but upon annealing the solid-solution phase stability is primarily governed by mutual miscibility.

  View details for DOI 10.1021/acscombsci.6b00077

  View details for Web of Science ID 000383213300009

  View details for PubMedID 27494349

• Measurement and Modeling of Short and Medium Range Order in Amorphous Ta2O5 Thin Films SCIENTIFIC REPORTS Shyam, B., Stone, K. H., Bassiri, R., Fejer, M. M., Toney, M. F., Mehta, A. 2016; 6

  Abstract

  Amorphous films and coatings are rapidly growing in importance. Yet, there is a dearth of high-quality structural data on sub-micron films. Not understanding how these materials assemble at atomic scale limits fundamental insights needed to improve their performance. Here, we use grazing-incidence x-ray total scattering measurements to examine the atomic structure of the top 50-100 nm of Ta2O5 films; mirror coatings that show high promise to significantly improve the sensitivity of the next generation of gravitational-wave detectors. Our measurements show noticeable changes well into medium range, not only between crystalline and amorphous, but also between as-deposited, annealed and doped amorphous films. It is a further challenge to quickly translate the structural information into insights into mechanisms of packing and disorder. Here, we illustrate a modeling approach that allows translation of observed structural features to a physically intuitive packing of a primary structural unit based on a kinked Ta-O-Ta backbone. Our modeling illustrates how Ta-O-Ta units link to form longer 1D chains and even 2D ribbons, and how doping and annealing influences formation of 2D order. We also find that all the amorphousTa2O5 films studied in here are not just poorly crystalline but appear to lack true 3D order.

  View details for DOI 10.1038/srep32170

  View details for Web of Science ID 000381970600001

  View details for PubMedID 27562542

  View details for PubMedCentralID PMC4999889

• Influence of amorphous structure on polymorphism in vanadia APL MATERIALS Stone, K. H., Schelhas, L. T., Garten, L. M., Shyam, B., Mehta, A., Ndione, P. F., Ginley, D. S., Toney, M. F. 2016; 4 (7)

  View details for DOI 10.1063/1.4958674

  View details for Web of Science ID 000382404300006

• Reverse Engineering Ancient Greek Ceramics: Morphological and Spectral Characterization of Replicates JOURNAL OF THE AMERICAN CERAMIC SOCIETY Cianchetta, I., Trentelman, K., Walton, M. S., Maish, J., Mehta, A., Foran, B. 2016; 99 (5): 1792-1801

  View details for DOI 10.1111/jace.14123

  View details for Web of Science ID 000374858500043

• Analytical imaging studies of the migration of degraded orpiment, realgar, and emerald green pigments in historic paintings and related conservation issues HERITAGE SCIENCE Keune, K., Mass, J., Mehta, A., Church, J., Meirer, F. 2016; 4

  View details for DOI 10.1186/s40494-016-0078-1

  View details for Web of Science ID 000374560000001

• Order, disorder and mixing: The atomic structure of amorphous mixtures of titania and tantala JOURNAL OF NON-CRYSTALLINE SOLIDS Bassiri, R., Abernathy, M. R., Liou, F., Mehta, A., Gustafson, E. K., Hart, M. J., Isa, H. N., Kim, N., Lin, A. C., MacLaren, I., Martin, I. W., Route, R. K., Rowan, S., Shyam, B., Stebbins, J. F., Fejer, M. M. 2016; 438: 59-66

  View details for DOI 10.1016/j.jnoncrysol.2016.02.009

  View details for Web of Science ID 000373545300008

• Voltage-Controlled Interfacial Layering in an Ionic Liquid on SrTiO3 ACS NANO Petach, T. A., Mehta, A., Marks, R., Johnson, B., Toney, M. F., Goldhaber-Gordon, D. 2016; 10 (4): 4565-4569

  Abstract

  One prominent structural feature of ionic liquids near surfaces is formation of alternating layers of anions and cations. However, how this layering responds to an applied potential is poorly understood. We focus on the structure of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate (BMPY-FAP) near the surface of a strontium titanate (SrTiO3) electric double-layer transistor. Using X-ray reflectivity, we show that at positive bias the individual layers in the ionic liquid double layer thicken and the layering persists further away from the interface. We model the reflectivity using a modified distorted crystal model with alternating cation and anion layers, which allows us to extract the charge density and the potential near the surface. We find that the charge density is strongly oscillatory with and without applied potential and that with an applied gate bias of 4.5 V the first two layers become significantly more cation rich than at zero bias, accumulating about 2.5 × 10(13) cm(-2) excess charge density.

  View details for DOI 10.1021/acsnano.6b00645

  View details for Web of Science ID 000375245000078

  View details for PubMedID 26959226

• Reverse engineering ancient Athenian pottery: A collaboration between cultural heritage, industry, and academia Trentelman, K., Cianchetta, I., Walton, M., Mehta, A., Pianetta, P., Foran, B., Saunders, D., Maish, J. AMER CHEMICAL SOC. 2016

  View details for Web of Science ID 000431903800476

• Thickness dependence of exchange coupling in (111)-oriented perovskite oxide superlattices PHYSICAL REVIEW B Jia, Y., Chopdekar, R. V., Arenholz, E., Liu, Z., Biegalski, M. D., Porter, Z. D., Mehta, A., Takamura, Y. 2016; 93 (10)

  View details for DOI 10.1103/PhysRevB.93.104403

  View details for Web of Science ID 000371400100003

• Strontium carbonate nanoparticles for the surface treatment of problematic sulfur and iron in waterlogged archaeological wood JOURNAL OF CULTURAL HERITAGE Schofield, E. J., Sarangi, R., Mehta, A., Jones, A. M., Smith, A., Mosselmans, J. F., Chadwick, A. V. 2016; 18: 306-312

  View details for DOI 10.1016/j.culher.2015.07.013

  View details for Web of Science ID 000372484800012

• Investigating the firing protocol of Athenian pottery production: A Raman study of replicate and ancient sherds JOURNAL OF RAMAN SPECTROSCOPY Cianchetta, I., Maish, J., Saunders, D., Walton, M., Mehta, A., Foran, B., Trentelman, K. 2015; 46 (10): 996-1002

  View details for DOI 10.1002/jrs.4662

  View details for Web of Science ID 000363090200026

• Exchange coupling in (111)-oriented La0.7Sr0.3MnO3/La0.7Sr0.3FeO3 superlattices PHYSICAL REVIEW B Jia, Y., Chopdekar, R. V., Arenholz, E., Young, A. T., Marcus, M. A., Mehta, A., Takamura, Y. 2015; 92 (9)

  View details for DOI 10.1103/PhysRevB.92.094407

  View details for Web of Science ID 000360522600001

• A high-throughput investigation of Fe-Cr-Al as a novel high-temperature coating for nuclear cladding materials NANOTECHNOLOGY Bunn, J., Fang, R. L., Albing, M. R., Mehta, A., Kramer, M. J., Besser, M. F., Hattrick-Simpers, J. R. 2015; 26 (27): 274003

  Abstract

  High-temperature alloy coatings that can resist oxidation are urgently needed as nuclear cladding materials to mitigate the danger of hydrogen explosions during meltdown. Here we apply a combination of computationally guided materials synthesis, high-throughput structural characterization and data analysis tools to investigate the feasibility of coatings from the Fe–Cr–Al alloy system. Composition-spread samples were synthesized to cover the region of the phase diagram previous bulk studies have identified as forming protective oxides. The metallurgical and oxide phase evolution were studied via in situ synchrotron glancing incidence x-ray diffraction at temperatures up to 690 K. A composition region with an Al concentration greater than 3.08 at%, and between 20.0 at% and 32.9 at% Cr showed the least overall oxide growth. Subsequently, a series of samples were deposited on stubs and their oxidation behavior at 1373 K was observed. The continued presence of a passivating oxide was confirmed in this region over a period of 6 h.

  View details for DOI 10.1088/0957-4484/26/27/274003

  View details for Web of Science ID 000356449100004

  View details for PubMedID 26086841

• Dimensionality Controlled Octahedral Symmetry-Mismatch and Functionalities in Epitaxial LaCoO3/SrTiO3 Heterostructures. Nano letters Qiao, L., Jang, J. H., Singh, D. J., Gai, Z., Xiao, H., Mehta, A., Vasudevan, R. K., Tselev, A., Feng, Z., Zhou, H., Li, S., Prellier, W., Zu, X., Liu, Z., Borisevich, A., Baddorf, A. P., Biegalski, M. D. 2015; 15 (7): 4677-4684

  Abstract

  Epitaxial strain provides a powerful approach to manipulate physical properties of materials through rigid compression or extension of their chemical bonds via lattice-mismatch. Although symmetry-mismatch can lead to new physics by stabilizing novel interfacial structures, challenges in obtaining atomic-level structural information as well as lack of a suitable approach to separate it from the parasitical lattice-mismatch have limited the development of this field. Here, we present unambiguous experimental evidence that the symmetry-mismatch can be strongly controlled by dimensionality and significantly impact the collective electronic and magnetic functionalities in ultrathin perovskite LaCoO3/SrTiO3 heterojunctions. State-of-art diffraction and microscopy reveal that symmetry breaking dramatically modifies the interfacial structure of CoO6 octahedral building-blocks, resulting in expanded octahedron volume, reduced covalent screening, and stronger electron correlations. Such phenomena fundamentally alter the electronic and magnetic behaviors of LaCoO3 thin-films. We conclude that for epitaxial systems, correlation strength can be tuned by changing orbital hybridization, thus affecting the Coulomb repulsion, U, instead of by changing the band structure as the common paradigm in bulks. These results clarify the origin of magnetic ordering for epitaxial LaCoO3 and provide a route to manipulate electron correlation and magnetic functionality by orbital engineering at oxide heterojunctions.

  View details for DOI 10.1021/acs.nanolett.5b01471

  View details for PubMedID 26103204

• Impact of symmetry on the ferroelectric properties of CaTiO₃ thin films (vol 106, 162904, 2015) APPLIED PHYSICS LETTERS Biegalski, M. D., Qiao, L., Gu, Y., Mehta, A., He, Q., Takamura, Y., Borisevich, A., Chen, L. 2015; 106 (21)

  View details for DOI 10.1063/1.4921711

  View details for Web of Science ID 000355631400054

• Impact of symmetry on the ferroelectric properties of CaTiO₃ thin films APPLIED PHYSICS LETTERS Biegalski, M. D., Qiao, L., Gu, Y., Mehta, A., He, Q., Takamura, Y., Borisevich, A., Chen, L. 2015; 106 (16)

  View details for DOI 10.1063/1.4918805

  View details for Web of Science ID 000353559900031

• Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5) APL MATERIALS Bassiri, R., Liou, F., Abernathy, M. R., Lin, A. C., Kim, N., Mehta, A., Shyam, B., Byer, R. L., Gustafson, E. K., Hart, M., MacLaren, I., Martin, I. W., Route, R. K., Rowan, S., Stebbins, J. F., Fejer, M. M. 2015; 3 (3)

  View details for DOI 10.1063/1.4913586

  View details for Web of Science ID 000352450200004

• Tracking the transformation and transport of arsenic sulfide pigments in paints: synchrotron-based X-ray micro-analyses JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY Keune, K., Mass, J., Meirer, F., Pottasch, C., van Loon, A., Hull, A., Church, J., Pouyet, E., Cotte, M., Mehta, A. 2015; 30 (3): 813-827

  View details for DOI 10.1039/c4ja00424h

  View details for Web of Science ID 000350650800028

• Effects of crystallinity and impurities on the electrical conductivity of Li-La-Zr-O thin films THIN SOLID FILMS Park, J. S., Cheng, L., Zorba, V., Mehta, A., Cabana, J., Chen, G., Doeff, M. M., Richardson, T. J., Park, J. H., Son, J., Hong, W. 2015; 576: 55-60

  View details for DOI 10.1016/j.tsf.2014.11.019

  View details for Web of Science ID 000349373300009

• Unconventional switching behavior in La_0.7Sr_0.3MnO₃/La_0.7Sr_0.3CoO₃ exchange-spring bilayers APPLIED PHYSICS LETTERS Li, B., Chopdekar, R. V., Arenholz, E., Mehta, A., Takamura, Y. 2014; 105 (20)

  View details for DOI 10.1063/1.4902115

  View details for Web of Science ID 000345513300045

• Interrelation between Structure - Magnetic Properties in La_0.5Sr_0.5CoO₃ ADVANCED MATERIALS INTERFACES Biegalski, M. D., Takamura, Y., Mehta, A., Gai, Z., Kalinin, S. V., Ambaye, H., Lauter, V., Fong, D., Pantelides, S. T., Kim, Y. M., He, J., Borisevich, A., Siemons, W., Christen, H. M. 2014; 1 (8)

  View details for DOI 10.1002/admi.201400203

  View details for Web of Science ID 000348285900014

• On-the-fly machine-learning for high-throughput experiments: search for rare-earth-free permanent magnets SCIENTIFIC REPORTS Kusne, A., Gao, T., Mehta, A., Ke, L., Manh Cuong Nguyen, Ho, K., Antropov, V., Wang, C., Kramer, M. J., Long, C., Takeuchi, I. 2014; 4: 6367

  Abstract

  Advanced materials characterization techniques with ever-growing data acquisition speed and storage capabilities represent a challenge in modern materials science, and new procedures to quickly assess and analyze the data are needed. Machine learning approaches are effective in reducing the complexity of data and rapidly homing in on the underlying trend in multi-dimensional data. Here, we show that by employing an algorithm called the mean shift theory to a large amount of diffraction data in high-throughput experimentation, one can streamline the process of delineating the structural evolution across compositional variations mapped on combinatorial libraries with minimal computational cost. Data collected at a synchrotron beamline are analyzed on the fly, and by integrating experimental data with the inorganic crystal structure database (ICSD), we can substantially enhance the accuracy in classifying the structural phases across ternary phase spaces. We have used this approach to identify a novel magnetic phase with enhanced magnetic anisotropy which is a candidate for rare-earth free permanent magnet.

  View details for DOI 10.1038/srep06367

  View details for Web of Science ID 000341937200007

  View details for PubMedID 25220062

  View details for PubMedCentralID PMC4163667

• Mechanism for the large conductance modulation in electrolyte-gated thin gold films PHYSICAL REVIEW B Petach, T. A., Lee, M., Davis, R. C., Mehta, A., Goldhaber-Gordon, D. 2014; 90 (8)

  View details for DOI 10.1103/PhysRevB.90.081108

  View details for Web of Science ID 000341256800001

• On the mechanism that leads to vanishing thermal hysteresis of the B2-R phase transformation in multilayered (TiNi)/(W) shape memory alloy thin films THIN SOLID FILMS Buenconsejo, P. S., Zarnetta, R., Young, M., Brunken, H., Mehta, A., Ludwig, A. 2014; 564: 79-85

  View details for DOI 10.1016/j.tsf.2014.05.010

  View details for Web of Science ID 000340852200008

• Sol-flame synthesis of cobalt-doped TiO2 nanowires with enhanced electrocatalytic activity for oxygen evolution reaction. Physical chemistry chemical physics Cai, L., Cho, I. S., Logar, M., Mehta, A., He, J., Lee, C. H., Rao, P. M., Feng, Y., Wilcox, J., Prinz, F. B., Zheng, X. 2014; 16 (24): 12299-12306

  Abstract

  Doping nanowires (NWs) is of crucial importance for a range of applications due to the unique properties arising from both impurities' incorporation and nanoscale dimensions. However, existing doping methods face the challenge of simultaneous control over the morphology, crystallinity, dopant distribution and concentration at the nanometer scale. Here, we present a controllable and reliable method, which combines versatile solution phase chemistry and rapid flame annealing process (sol-flame), to dope TiO2 NWs with cobalt (Co). The sol-flame doping method not only preserves the morphology and crystallinity of the TiO2 NWs, but also allows fine control over the Co dopant profile by varying the concentration of Co precursor solution. Characterizations of the TiO2:Co NWs show that Co dopants exhibit 2+ oxidation state and substitutionally occupy Ti sites in the TiO2 lattice. The Co dopant concentration significantly affects the oxygen evolution reaction (OER) activity of TiO2:Co NWs, and the TiO2:Co NWs with 12 at% of Co on the surface show the highest OER activity with a 0.76 V reduction of the overpotential with respect to undoped TiO2 NWs. This enhancement of OER activity for TiO2:Co NWs is attributed to both improved surface charge transfer kinetics and increased bulk conductivity.

  View details for DOI 10.1039/c4cp01748j

  View details for PubMedID 24820239

• Learning from the past: Rare epsilon-Fe2O3 in the ancient black-glazed Jian (Tenmoku) wares SCIENTIFIC REPORTS Dejoie, C., Sciau, P., Li, W., Noe, L., Mehta, A., Chen, K., Luo, H., Kunz, M., Tamura, N., Liu, Z. 2014; 4

  Abstract

  Ancient Jian wares are famous for their lustrous black glaze that exhibits unique colored patterns. Some striking examples include the brownish colored "Hare's Fur" (HF) strips and the silvery "Oil Spot" (OS) patterns. Herein, we investigated the glaze surface of HF and OS samples using a variety of characterization methods. Contrary to the commonly accepted theory, we identified the presence of ε-Fe2O3, a rare metastable polymorph of Fe2O3 with unique magnetic properties, in both HF and OS samples. We found that surface crystals of OS samples are up to several micrometers in size and exclusively made of ε-Fe2O3. Interestingly, these ε-Fe2O3 crystals on the OS sample surface are organized in a periodic two dimensional fashion. These results shed new lights on the actual mechanisms and kinetics of polymorphous transitions of Fe2O3. Deciphering technologies behind the fabrication of ancient Jian wares can thus potentially help researchers improve the ε-Fe2O3 synthesis.

  View details for DOI 10.1038/srep04941

  View details for Web of Science ID 000335725100003

  View details for PubMedID 24820819

• Magnetic ordering of implanted Mn in HOPG substrates PHYSICAL REVIEW B Guchhait, S., Ohldag, H., Arenholz, E., Ferrer, D. A., Mehta, A., Banerjee, S. K. 2013; 88 (17)

  View details for DOI 10.1103/PhysRevB.88.174425

  View details for Web of Science ID 000327933500004

• Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques JOVE-JOURNAL OF VISUALIZED EXPERIMENTS Doeff, M. M., Chen, G., Cabana, J., Richardson, T. J., Mehta, A., Shirpour, M., Duncan, H., Kim, C., Kam, K. C., Conry, T. 2013: e50594

  Abstract

  Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g. changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g. on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

  View details for DOI 10.3791/50594

  View details for Web of Science ID 000209228900011

  View details for PubMedID 24300777

  View details for PubMedCentralID PMC3989498

• Material Evidence for Multiple Firings of Ancient Athenian Red-Figure Pottery JOURNAL OF THE AMERICAN CERAMIC SOCIETY Walton, M., Trentelman, K., Cummings, M., Poretti, G., Maish, J., Saunders, D., Foran, B., Brodie, M., Mehta, A. 2013; 96 (7): 2031-2035

  View details for DOI 10.1111/jace.12395

  View details for Web of Science ID 000327187800002

• Formation of arsenolite crystals at room temperature after very high dose arsenic implantation in silicon APPLIED PHYSICS LETTERS Meirer, F., Giubertoni, D., Demenev, E., Vanzetti, L., Gennaro, S., Fedrizzi, M., Pepponi, G., Mehta, A., Pianetta, P., Steinhauser, G., Vishwanath, V., Foad, M., Bersani, M. 2012; 101 (23)

  View details for DOI 10.1063/1.4769446

  View details for Web of Science ID 000312243900039

• Structural Underpinnings of the Enhanced Cycling Stability upon Al-Substitution in LiNi0.45Mn0.45Co0.1-yAlyO2 Positive Electrode Materials for Li-ion Batteries CHEMISTRY OF MATERIALS Conry, T. E., Mehta, A., Cabana, J., Doeff, M. M. 2012; 24 (17): 3307-3317

  View details for DOI 10.1021/cm3011937

  View details for Web of Science ID 000308833400002

• 3D elemental sensitive imaging using transmission X-ray microscopy ANALYTICAL AND BIOANALYTICAL CHEMISTRY Liu, Y., Meirer, F., Wang, J., Requena, G., Williams, P., Nelson, J., Mehta, A., Andrews, J. C., Pianetta, P. 2012; 404 (5): 1297-1301

  Abstract

  Determination of the heterogeneous distribution of metals in alloy/battery/catalyst and biological materials is critical to fully characterize and/or evaluate the functionality of the materials. Using synchrotron-based transmission x-ray microscopy (TXM), it is now feasible to perform nanoscale-resolution imaging over a wide X-ray energy range covering the absorption edges of many elements; combining elemental sensitive imaging with determination of sample morphology. We present an efficient and reliable methodology to perform 3D elemental sensitive imaging with excellent sample penetration (tens of microns) using hard X-ray TXM. A sample of an Al-Si piston alloy is used to demonstrate the capability of the proposed method.

  View details for DOI 10.1007/s00216-012-5818-9

  View details for Web of Science ID 000307957800004

  View details for PubMedID 22349401

• Oxidative Dissolution of Biogenic Uraninite in Groundwater at Old Rifle, CO (vol 45, pg 8748, 2011) ENVIRONMENTAL SCIENCE & TECHNOLOGY Campbell, K. M., Veeramani, H., Ulrich, K., Blue, L. Y., Giammar, D. E., Bernier-Latmani, R., Stubbs, J. E., Suvorova, E., Yabusaki, S., Lezama-Pacheco, J. S., Mehta, A., Long, P. E., Bargar, J. R. 2012; 46 (16): 9199

  View details for DOI 10.1021/es302732d

  View details for Web of Science ID 000307697700081

• XAFS Investigations of LiNi0.45Mn0.45Co0.1-yAlyO2 Positive Electrode Materials JOURNAL OF THE ELECTROCHEMICAL SOCIETY Conry, T. E., Mehta, A., Cabana, J., Doeff, M. M. 2012; 159 (9): A1562-A1571

  View details for DOI 10.1149/2.048209jes

  View details for Web of Science ID 000309104400023

• Electrochemical and Physical Properties of Ti-Substituted Layered Nickel Manganese Cobalt Oxide (NMC) Cathode Materials JOURNAL OF THE ELECTROCHEMICAL SOCIETY Kam, K. C., Mehta, A., Heron, J. T., Doeff, M. M. 2012; 159 (8): A1383-A1392

  View details for DOI 10.1149/2.060208jes

  View details for Web of Science ID 000308559400039

• Electron bombardment of films used for reducing spurious charge in electrostatic electron optics JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Maldonado, J. R., Pease, F., Hitzman, C. J., Brodie, A. D., Petric, P., Bevis, C., McCord, M., Tong, W. M., Kidwingira, F., Pianetta, P., Bibee, M., Mehta, A., Bhatia, R. 2011; 29 (6)

  View details for DOI 10.1116/1.3663957

  View details for Web of Science ID 000298538800025

• Giant magnetostriction in annealed Co1-xFex thin-films NATURE COMMUNICATIONS Hunter, D., Osborn, W., Wang, K., Kazantseva, N., Hattrick-Simpers, J., Suchoski, R., Takahashi, R., Young, M. L., Mehta, A., Bendersky, L. A., Lofland, S. E., Wuttig, M., Takeuchi, I. 2011; 2

  Abstract

  Chemical and structural heterogeneity and the resulting interaction of coexisting phases can lead to extraordinary behaviours in oxides, as observed in piezoelectric materials at morphotropic phase boundaries and relaxor ferroelectrics. However, such phenomena are rare in metallic alloys. Here we show that, by tuning the presence of structural heterogeneity in textured Co(1-x)Fe(x) thin films, effective magnetostriction λ(eff) as large as 260 p.p.m. can be achieved at low-saturation field of ~10 mT. Assuming λ(100) is the dominant component, this number translates to an upper limit of magnetostriction of λ(100)≈5λ(eff) >1,000 p.p.m. Microstructural analyses of Co(1-x)Fe(x) films indicate that maximal magnetostriction occurs at compositions near the (fcc+bcc)/bcc phase boundary and originates from precipitation of an equilibrium Co-rich fcc phase embedded in a Fe-rich bcc matrix. The results indicate that the recently proposed heterogeneous magnetostriction mechanism can be used to guide exploration of compounds with unusual magnetoelastic properties.

  View details for DOI 10.1038/ncomms1529

  View details for Web of Science ID 000297686500005

  View details for PubMedID 22044997

• Oxidative Dissolution of Biogenic Uraninite in Groundwater at Old Rifle, CO ENVIRONMENTAL SCIENCE & TECHNOLOGY Campbell, K. M., Veeramani, H., Urich, K., Blue, L. Y., Giammar, D. E., Bernier-Latmani, R., Stubbs, J. E., Suvorova, E., Yabusaki, S., Lezama-Pacheco, J. S., Mehta, A., Long, P. E., Bargar, J. R. 2011; 45 (20): 8748-8754

  Abstract

  Reductive bioremediation is currently being explored as a possible strategy for uranium-contaminated aquifers such as the Old Rifle site (Colorado). The stability of U(IV) phases under oxidizing conditions is key to the performance of this procedure. An in situ method was developed to study oxidative dissolution of biogenic uraninite (UO₂), a desirable U(VI) bioreduction product, in the Old Rifle, CO, aquifer under different variable oxygen conditions. Overall uranium loss rates were 50-100 times slower than laboratory rates. After accounting for molecular diffusion through the sample holders, a reactive transport model using laboratory dissolution rates was able to predict overall uranium loss. The presence of biomass further retarded diffusion and oxidation rates. These results confirm the importance of diffusion in controlling in-aquifer U(IV) oxidation rates. Upon retrieval, uraninite was found to be free of U(VI), indicating dissolution occurred via oxidation and removal of surface atoms. Interaction of groundwater solutes such as Ca²⁺ or silicate with uraninite surfaces also may retard in-aquifer U loss rates. These results indicate that the prolonged stability of U(IV) species in aquifers is strongly influenced by permeability, the presence of bacterial cells and cell exudates, and groundwater geochemistry.

  View details for DOI 10.1021/es200482f

  View details for Web of Science ID 000295704500022

  View details for PubMedID 21910475

• Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy JOURNAL OF SYNCHROTRON RADIATION Meirer, F., Cabana, J., Liu, Y., Mehta, A., Andrews, J. C., Pianetta, P. 2011; 18: 773-781

  Abstract

  The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano- and micrometer-scale factors at the origin of macroscopic behavior. While different electron- and X-ray-based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X-ray imaging set-up is proposed, combining full-field transmission X-ray microscopy (TXM) with X-ray absorption near-edge structure (XANES) spectroscopy to follow two-dimensional and three-dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.

  View details for DOI 10.1107/S0909049511019364

  View details for Web of Science ID 000294821600014

  View details for PubMedID 21862859

  View details for PubMedCentralID PMC3161818

• Nanoparticle de-acidification of the Mary Rose MATERIALS TODAY Schofield, E. J., Sarangi, R., Mehta, A., Jones, A. M., Mosselmans, F. J., Chadwick, A. V. 2011; 14 (7-8): 354-358

  View details for Web of Science ID 000292497100017

• Material evidence for the use of Attic white-ground lekythoi ceramics in cremation burials JOURNAL OF ARCHAEOLOGICAL SCIENCE Walton, M. S., Svoboda, M., Mehta, A., Webb, S., Trentelman, K. 2010; 37 (5): 936-940

  View details for DOI 10.1016/j.jas.2009.11.026

  View details for Web of Science ID 000276786700004

• Effect of Mn(II) on the Structure and Reactivity of Biogenic Uraninite ENVIRONMENTAL SCIENCE & TECHNOLOGY Veeramani, H., Schofield, E. J., Sharp, J. O., Suvorova, E. I., Ulrich, K., Mehta, A., Giammar, D. E., Bargar, J. R., Bernier-Latmani, R. 2009; 43 (17): 6541-6547

  Abstract

  The efficacy of a site remediation strategy involving the stimulaton of microbial U(VI) reduction hinges in part upon the long-term stability of the product, biogenic uraninite, toward environmental oxidants. Geological sedimentary uraninites (nominal formula UO2) reportedly contain abundant cation impurities that enhance their resistance to oxidation. By analogy, incorporation of common groundwater solutes into biogenic uraninite could also impart stability-enhancing properties. Mn(II) is a common groundwater cation, which has a favorable ionic radiusfor substitution reactions. The structure and reactivity of Mn(II)-reacted biogenic uraninite are investigated in this study. Up to 4.4 weight percent Mn(II) was found to be structurally bound in biogenic uraninite. This Mn(II) incorporation was associated with decreasing uraninite particle size and structural order. Importantly, the equilibrium solubility of Mn-reacted uraninite was halved relative to unreacted uraninite, demonstrating changes in thermodynamic properties, while the dissolution rate was up to 38-fold lower than that of unreacted biogenic uraninite. We conclude that structuralincorporation of Mn(II) into uraninite has an important stabilizing effect leading to the prediction that other groundwater solutes may similarly stabilize biogenic uraninite.

  View details for DOI 10.1021/es900556k

  View details for Web of Science ID 000269258000021

  View details for PubMedID 19764214

• Manganese incorporation into biogenic uraninite affects its oxidative stability 19th Annual VM Goldschmidt Conference Veeramani, H., Sharp, J. O., Suvorova, E. I., Schofield, E., Ulrich, K., Mehta, A., Giammar, D. E., Bargar, J. R., Bernier-Latmani, R. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A1376–A1376

  View details for Web of Science ID 000267229903440

• Structure, composition, size and reactivity of biogenic nano-uraninite 19th Annual VM Goldschmidt Conference Bargar, J. R., Bernier-Latmani, R., Giammar, D. E., Mehta, A., Schofield, E., Sharp, J. O., Suvorova, E. I., Ulrich, K., Veeramani, H. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A87–A87

  View details for Web of Science ID 000267229900187

• How do biogeochemical conditions affect the products of U(VI) reduction by bacteria? Bernier-Latmani, R., Sharp, J. O., Veeramani, H., Suvorova, E. I., Schofield, E., Bargar, J. R., Mehta, A., Ulrich, K., Giammar, D. E. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207857804284

• The Interaction of Bromide Ions with Graphitic Materials ADVANCED MATERIALS Mehta, A., Nelson, E. J., Webb, S. M., Holt, J. K. 2009; 21 (1): 102-106

  View details for DOI 10.1002/adma.200801602

  View details for Web of Science ID 000262586300014

• Surface Structure of KIO3 Grown by Heterogeneous Reaction of Ozone with KI (001) JOURNAL OF PHYSICAL CHEMISTRY C Brown, M. A., Liu, Z., Ashby, P. D., Mehta, A., Grimm, R. L., Hemminger, J. C. 2008; 112 (47): 18287-18290

  View details for DOI 10.1021/jp807113d

  View details for Web of Science ID 000261056500001

• Structure of Biogenic Uraninite Produced by Shewanella oneidensis Strain MR-1 ENVIRONMENTAL SCIENCE & TECHNOLOGY Schofield, E. J., Veeramani, H., Sharp, J. O., Suvorova, E., Bernier-Latmani, R., Mehta, A., Stahlman, J., Webb, S. M., Clark, D. L., Conradson, S. D., Ilton, E. S., Bargar, J. R. 2008; 42 (21): 7898-7904

  Abstract

  The stability of biogenic uraninite with respect to oxidation is seminal to the success of in situ bioreduction strategies for remediation of subsurface U(VI) contamination. The properties and hence stability of uraninite are dependent on its size, structure, and composition. In this study, the local-, intermediate-, and long-range molecular-scale structure of nanoscale uraninite produced by Shewanella oneidensis strain MR-1 was investigated using EXAFS, SR-based powder diffraction and TEM. The uraninite products were found to be structurally homologous with stoichiometric U02 under all conditions considered. Significantly, there was no evidence for lattice strain of the biogenic uraninite nanoparticles. The fresh nanoparticles were found to exhibit a well-ordered interior core of diameter ca. 1.3 nm and an outer region of thickness ca approximately 0.6 nm in which the structure is locally distorted. The lack of nanoparticle strain and structural homology with stoichiometric U02 suggests that established thermodynamic parameters for the latter material are an appropriate starting point to model the behavior of nanobiogenic uraninite. The detailed structural analysis in this study provides an essential foundation for subsequent investigations of environmental samples.

  View details for DOI 10.1021/es800579g

  View details for Web of Science ID 000260561200031

  View details for PubMedID 19031878

• GEOC 32-Structural identity and reactivity of biogenic UO2 236th National Meeting of the American-Chemical-Society Bargar, J. R., Schofield, E., Mehta, A., Veeramani, H., Ulrich, K., Sharp, J., Bernier-Latmani, R., Giammar, D. E., Conradson, S. D., Clark, D. L. AMER CHEMICAL SOC. 2008

  View details for Web of Science ID 000270256304803

• The single-layered morphology of supported MoS2-based catalysts - The role of the cobalt promoter and its effects in the hydrodesulfurization of dibenzothiophene APPLIED CATALYSIS A-GENERAL Berhault, G., De la Rosa, M. P., Mehta, A., Yacaman, M. J., Chianelli, R. R. 2008; 345 (1): 80-88

  View details for DOI 10.1016/j.apcata.2008.04.034

  View details for Web of Science ID 000257961300010

• Ultrahigh-Resolution <i>In Situ</i> Diffraction Characterization of the Local Mechanics at a Growing Crack Tip in Nitinol Robertson, S. W., Ritchie, R. O., Mehta, A., Gong, X., Pelton, A. R., Berg, B., Mitchell, M. R., Proft, J. ASM INTERNATIONAL. 2008: 35-+

  View details for DOI 10.1361/cp2006smst035

  View details for Web of Science ID 000281128400004

• Understanding the deformation and fracture of nitinol endovascular stents using in situ synchrotron X-ray microdiffraction ADVANCED MATERIALS Mehta, A., Gong, X., Imbeni, V., Pelton, A. R., Ritchie, R. O. 2007; 19 (9): 1183-?

  View details for DOI 10.1002/adma.200601916

  View details for Web of Science ID 000246658100002

• Synchrotron X-ray reflectivity studies of nanoporous organosilicate thin films with low dielectric constants 13th International Conference on Small-Angle Scattering Oh, W., Hwang, Y., Shin, T. J., Lee, B., Kim, J., Yoon, J., Brennan, S., Mehta, A., Ree, M. WILEY-BLACKWELL. 2007: S626–S630

  View details for DOI 10.1107/S0021889806047509

  View details for Web of Science ID 000246059800127

• Synchrotron and simulations techniques applied to problems in materials science: catalysts and Azul Maya pigments Symposium on Applications of Synchrotron Radiation to Materials Chianelli, R. R., De la Rosa, M. P., Meitzner, G., Siadati, M., Berhault, G., Mehta, A., Pople, J., Fuentes, S., Alonzo-Nunez, G., Polette, L. A. WILEY-BLACKWELL PUBLISHING, INC. 2005: 129–134

  Abstract

  Development of synchrotron techniques for the determination of the structure of disordered, amorphous and surface materials has exploded over the past 20 years owing to the increasing availability of high-flux synchrotron radiation and the continuing development of increasingly powerful synchrotron techniques. These techniques are available to materials scientists who are not necessarily synchrotron scientists through interaction with effective user communities that exist at synchrotrons such as the Stanford Synchrotron Radiation Laboratory. In this article the application of multiple synchrotron characterization techniques to two classes of materials defined as 'surface compounds' is reviewed. One class of surface compounds are materials like MoS(2-x)C(x) that are widely used petroleum catalysts, used to improve the environmental properties of transportation fuels. These compounds may be viewed as 'sulfide-supported carbides' in their catalytically active states. The second class of 'surface compounds' are the 'Maya blue' pigments that are based on technology created by the ancient Maya. These compounds are organic/inorganic 'surface complexes' consisting of the dye indigo and palygorskite, common clay. The identification of both surface compounds relies on the application of synchrotron techniques as described here.

  View details for DOI 10.1107/S0909049504026172

  View details for Web of Science ID 000227377200003

  View details for PubMedID 15728965