@article{smith_sawant_zeng_eldred_wu_greeley_gao_2024, title={Disproportionation chemistry in K<sub>2</sub>PtCl<sub>4</sub> visualized at atomic resolution using scanning transmission electron microscopy}, volume={10}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.adi0175}, abstractNote={The direct observation of a solid-state chemical reaction can reveal otherwise hidden mechanisms that control the reaction kinetics. However, probing the chemical bond breaking and formation at the molecular level remains challenging because of the insufficient spatial-temporal resolution and composition analysis of available characterization methods. Using atomic-resolution differential phase-contrast imaging in scanning transmission electron microscopy, we have visualized the decomposition chemistry of K 2 PtCl 4 to identify its transient intermediate phases and their interfaces that characterize the chemical reduction process. The crystalline structure of K 2 PtCl 4 is found to undergo a disproportionation reaction to form K 2 PtCl 6 , followed by gradual reduction to crystalline Pt metal and KCl. By directly imaging different Pt─Cl bond configurations and comparing them to models predicted via density functional theory calculations, a causal connection between the initial and final states of a chemical reaction is established, showcasing new opportunities to resolve reaction pathways through atomistic experimental visualization.}, number={6}, journal={SCIENCE ADVANCES}, author={Smith, Jacob G. and Sawant, Kaustubh J. and Zeng, Zhenhua and Eldred, Tim B. and Wu, Jianbo and Greeley, Jeffrey P. and Gao, Wenpei}, year={2024}, month={Feb} }
 @article{zhou_li_brady_eldred_garcia_ma_wang_hu_li_liu_2024, title={Long-term oxidation and chromium evaporation behavior of Al2O3-forming austenitic stainless steel for 900 °C balance-of-plant components applications in solid oxide fuel cells}, volume={50}, ISSN={["1879-3487"]}, DOI={10.1016/j.ijhydene.2023.10.041}, abstractNote={The long-term operation of balance-of-plant (BoP) components in solid oxide fuel cells (SOFCs) relies on the presence of a stable and durable oxide layer. In this study, we investigate the oxidation and chromium (Cr) evaporation behaviors of two developmental alumina-forming austenitic (AFA) alloys compared to chromia-forming alloy 625 at 900 °C in air with 10% water vapor. Transpiration tests, weight gain tests, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and scanning transmission electron microscopy with energy dispersive X-ray analysis are employed to evaluate the oxidation and Cr evaporation behaviors. Our findings reveal that alloy 625 exhibits significantly higher rates of Cr evaporation compared to OC11 (Y and Hf additions) and OC11LZ (Y and Zr additions), with evaporation amounts ∼56 and ∼28 times greater, respectively. The observed differences between OC11 and OC11LZ can be attributed to variations in the formed oxide scales during long-term operation. Furthermore, we examine the influence of Hf and Zr reactive elements on the long-term oxidation and chromium evaporation behaviors, providing insights into the role of these elements in enhancing the performance and stability of the alloys.}, journal={INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, author={Zhou, Lingfeng and Li, Wenyuan and Brady, Michael P. and Eldred, Tim B. and Garcia, Roberto and Ma, Liang and Wang, Yi and Hu, Shanshan and Li, Wei and Liu, Xingbo}, year={2024}, month={Jan}, pages={1109–1125} }
 @article{rathkanthiwar_reddy_quinones_loveless_kamiyama_bagheri_khachariya_eldred_moody_mita_et al._2023, title={Anderson transition in compositionally graded p-AlGaN}, volume={134}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0176419}, DOI={10.1063/5.0176419}, abstractNote={Mg-doped, graded AlGaN films showed the formation of an impurity band and high, temperature-invariant p-conductivity even for doping levels well below the Mott transition. However, compensating point defects disrupted the impurity band, resulting in an Anderson transition from the impurity band to valence band conduction and a more than tenfold reduction in room-temperature conductivity. This is the first demonstration of Anderson-like localization in AlGaN films.}, number={19}, journal={JOURNAL OF APPLIED PHYSICS}, author={Rathkanthiwar, Shashwat and Reddy, Pramod and Quinones, Cristyan E. and Loveless, James and Kamiyama, Masahiro and Bagheri, Pegah and Khachariya, Dolar and Eldred, Tim and Moody, Baxter and Mita, Seiji and et al.}, year={2023}, month={Nov} }
 @article{chi_ou_eldred_gao_kwon_murray_dreyer_butera_foucher_ambaye_et al._2023, title={Strain-tunable Berry curvature in quasi-two-dimensional chromium telluride}, volume={14}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-023-38995-4}, abstractNote={Magnetic transition metal chalcogenides form an emerging platform for exploring spin-orbit driven Berry phase phenomena owing to the nontrivial interplay between topology and magnetism. Here we show that the anomalous Hall effect in pristine Cr2Te3 thin films manifests a unique temperature-dependent sign reversal at nonzero magnetization, resulting from the momentum-space Berry curvature as established by first-principles simulations. The sign change is strain tunable, enabled by the sharp and well-defined substrate/film interface in the quasi-two-dimensional Cr2Te3 epitaxial films, revealed by scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. This Berry phase effect further introduces hump-shaped Hall peaks in pristine Cr2Te3 near the coercive field during the magnetization switching process, owing to the presence of strain-modulated magnetic layers/domains. The versatile interface tunability of Berry curvature in Cr2Te3 thin films offers new opportunities for topological electronics.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Chi, Hang and Ou, Yunbo and Eldred, Tim B. and Gao, Wenpei and Kwon, Sohee and Murray, Joseph and Dreyer, Michael and Butera, Robert E. and Foucher, Alexandre C. and Ambaye, Haile and et al.}, year={2023}, month={Jun} }
 @article{gao_wang_corolla_eldred_bose_gao_li_2022, title={Alkali metal halide-coated perovskite redox catalysts for anaerobic oxidative dehydrogenation of n-butane}, volume={8}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.abo7343}, DOI={10.1126/sciadv.abo7343}, abstractNote={Oxidative dehydrogenation (ODH) of n-butane has the potential to efficiently produce butadiene without equilibrium limitation or coke formation. Despite extensive research efforts, single-pass butadiene yields are limited to <23% in conventional catalytic ODH with gaseous O2. This article reports molten LiBr as an effective promoter to modify a redox-active perovskite oxide, i.e., La0.8Sr0.2FeO3 (LSF), for chemical looping–oxidative dehydrogenation of n-butane (CL-ODHB). Under the working state, the redox catalyst is composed of a molten LiBr layer covering the solid LSF substrate. Characterizations and ab initio molecular dynamics (AIMD) simulations indicate that peroxide species formed on LSF react with molten LiBr to form active atomic Br, which act as reaction intermediates for C─H bond activation. Meanwhile, molten LiBr layer inhibits unselective CO2 formation, leading to 42.5% butadiene yield. The redox catalyst design strategy can be extended to CL-ODH of other light alkanes such as iso-butane conversion to iso-butylene, providing a generalized approach for olefin production.}, number={30}, journal={SCIENCE ADVANCES}, author={Gao, Yunfei and Wang, Xijun and Corolla, Noel and Eldred, Tim and Bose, Arnab and Gao, Wenpei and Li, Fanxing}, year={2022}, month={Jul} }
 @article{zhou_brady_li_eldred_garcia_zeng_ma_wang_hu_liu_2022, title={Alumina-forming austenitic stainless steel for high durability and chromium-evaporation minimized balance of plant components in solid oxide fuel cells}, volume={47}, ISSN={["1879-3487"]}, DOI={10.1016/j.ijhydene.2022.09.010}, abstractNote={The chromium evaporation and oxidation behaviors of alumina-forming austenitic stainless steels are systematically investigated at 800 °C in air +10% H2O relative to 310S for 5000 h. Cr evaporation rates of 310S are about 35 times higher than AFA alloys after 5000 h. Relatively rapid oxidation is observed on 310S after only one 500 h cycle, followed by a modest degree of mass loss and spallation, while the AFA alloys show high oxidation resistance throughout the entire test. Continuous inner alumina layer formed on AFA alloys stays compact and stable after 5000 h which greatly reduces the Cr evaporation.}, number={90}, journal={INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, author={Zhou, Lingfeng and Brady, Michael P. and Li, Wenyuan and Eldred, Tim B. and Garcia, Roberto and Zeng, Zhipeng and Ma, Liang and Wang, Yi and Hu, Shanshan and Liu, Xingbo}, year={2022}, month={Nov}, pages={38334–38347} }
 @article{wang_eldred_smith_gao_2022, title={AutoDisk: Automated diffraction processing and strain mapping in 4D-STEM}, volume={236}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2022.113513}, abstractNote={Development in lattice strain mapping using four-dimensional scanning transmission electron microscopy (4D-STEM) method now offers improved precision and feasibility. However, automatic and accurate diffraction analysis is still challenging due to noise and the complexity of intensity in diffraction patterns. In this work, we demonstrate an approach, employing the blob detection on cross-correlated diffraction patterns followed by a lattice fitting algorithm, to automate the processing of four-dimensional data, including identifying and locating disks, and extracting local lattice parameters without prior knowledge about the material. The approach is both tested using simulated diffraction patterns and applied on experimental data acquired from a Pd@Pt core-shell nanoparticle. Our method shows robustness against various sample thicknesses and high noise, capability to handle complex patterns, and picometer-scale accuracy in strain measurement, making it a promising tool for high-throughput 4D-STEM data processing.}, journal={ULTRAMICROSCOPY}, author={Wang, Sihan and Eldred, Tim B. and Smith, Jacob G. and Gao, Wenpei}, year={2022}, month={Jun} }
 @article{zhou_finklea_li_shi_brady_eldred_garcia_tian_ma_wang_et al._2022, title={Deconvolution of deterioration of anode-supported cells by chromium poisoning from alumina-forming austenitic stainless steels for balance of plant applications in solid oxide fuel cells}, volume={428}, ISSN={["1873-3859"]}, DOI={10.1016/j.electacta.2022.140933}, abstractNote={Al2O3-forming austenitic (AFA) stainless steels are potential replacements for the existing balance of plant (BoP) components in solid oxide fuel cells (SOFCs). In this study, chromium (Cr) poisoning of anode supported cells (ASCs) coupled with various alloys was analyzed by the distribution of relaxation times (DRT). The performance deterioration of ASCs was mainly attributed to the increased polarization resistances of chemisorption of oxygen on the cathode and the oxygen diffusion and reaction in the cathode. The superior performance of ASC coupled with AFA alloys was due to the formed continuous alumina layer which can vastly decrease the evaporated gaseous Cr species, thus alleviating the Cr poisoning on the cathode region.}, journal={ELECTROCHIMICA ACTA}, author={Zhou, Lingfeng and Finklea, Harry O. and Li, Wenyuan and Shi, Wangying and Brady, Michael P. and Eldred, Tim B. and Garcia, Roberto and Tian, Hanchen and Ma, Liang and Wang, Yi and et al.}, year={2022}, month={Oct} }
 @article{szymanski_khachariya_eldred_bagheri_washiyama_chang_pavlidis_kirste_reddy_kohn_et al._2022, title={GaN lateral polar junction arrays with 3D control of doping by supersaturation modulated growth: A path toward III-nitride superjunctions}, volume={131}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0076044}, DOI={10.1063/5.0076044}, abstractNote={We demonstrate a pathway employing crystal polarity controlled asymmetric impurity incorporation in the wide bandgap nitride material system to enable 3D doping control during the crystal growth process. The pathway involves polarity specific supersaturation modulated growth of lateral polar structures of alternating Ga- and N-polar GaN domains. A STEM technique of integrated differential phase contrast is used to image the atomic structure of the different polar domains and their single atomic plane boundaries. As a demonstration, 1 μm wide alternating Ga- and N-polar GaN domains exhibiting charge balanced and periodic domains for superjunction technology were grown. The challenges in characterizing the resulting 3D doping profile were addressed with atom probe tomography with atomic scale compositional resolution corroborating capacitance measurements and secondary-ion mass spectroscopy analysis.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Szymanski, Dennis and Khachariya, Dolar and Eldred, Tim B. and Bagheri, Pegah and Washiyama, Shun and Chang, Alexander and Pavlidis, Spyridon and Kirste, Ronny and Reddy, Pramod and Kohn, Erhard and et al.}, year={2022}, month={Jan} }
 @article{eldred_smith_gao_2022, title={Polarization fluctuation of BaTiO3 at unit cell level mapped by four-dimensional scanning transmission electron microscopy}, volume={40}, ISSN={["1520-8559"]}, DOI={10.1116/6.0001451}, abstractNote={Diffraction analysis in four-dimensional scanning transmission electron microscopy now enables the mapping of local structures including symmetry, strain, and polarization of materials. However, measuring the distribution of these configurations at the unit cell level remains a challenge because most analysis methods require the diffraction disks to be separated, limiting the electron probe sizes to be larger than a unit cell. Here, we show improved spatial resolution in mapping the polarization displacement and phases of BaTiO3 sampled at a rate equivalent to the size of the projected unit cells using 4D-STEM. This improvement in spatial resolution is accomplished by masking out the overlapping regions in partially overlapped convergent beam electron diffraction patterns. By reducing the probe size to the order of single projected unit cells in size, the measurement shows local fluctuation within the nanosized rhombohedral domains in tetragonal phased BaTiO3, indicating the origin of phase transition and evolution across different length scales.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Eldred, Tim B. and Smith, Jacob G. and Gao, Wenpei}, year={2022}, month={Jan} }
 @article{su_chen_xu_eldred_smith_dellarova_wang_gao_2022, title={Visualizing the Formation of High-Entropy Fluorite Oxides from an Amorphous Precursor at Atomic Resolution}, volume={12}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.2c09760}, abstractNote={High-entropy oxides (HEOs) have a large tuning space in composition and crystal structures, offering the possibility for improved material properties in applications including catalysis, energy storage, and thermal barrier coatings. Understanding the nucleation and growth mechanisms of HEOs at the atomic scale is critical to the design of their structure and functions but remains challenging. Herein, we visualize the entire formation process of a high-entropy fluorite oxide from a polymeric precursor using atomic resolution in situ gas-phase scanning transmission electron microscopy. The results show a four-stage formation mechanism, including nucleation during the oxidation of a polymeric precursor below 400 °C, diffusive grain growth below 900 °C, liquid-phase-assisted compositional homogenization under a "state of supercooling" at 900 °C, and entropy-driven recrystallization and stabilization at higher temperatures. The atomistic insights are critical for the rational synthesis of HEOs with controlled grain sizes and morphologies and thus the related properties.}, journal={ACS NANO}, author={Su, Lei and Chen, Xi and Xu, Liang and Eldred, Tim and Smith, Jacob and DellaRova, Cierra and Wang, Hongjie and Gao, Wenpei}, year={2022}, month={Dec} }
 @article{wang_sun_brady_fleischmann_eldred_gao_wang_jiang_augustyn_2021, title={Fast Proton Insertion in Layered H2W2O7 via Selective Etching of an Aurivillius Phase}, volume={11}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.202003335}, abstractNote={H2W2O7, a metastable material synthesized via selective etching of the Aurivillius‐related Bi2W2O9, is demonstrated as an electrode for high power proton‐based energy storage. Comprehensive structural characterization is performed to obtain a high‐fidelity crystal structure of H2W2O7 using an iterative approach that combines X‐ray diffraction, neutron pair distribution function, scanning transmission electron microscopy, Raman spectroscopy, and density functional theory modeling. Electrochemical characterization shows a capacity retention of ≈80% at 1000 mV s–1 (1.5‐s charge/discharge time) as compared to 1 mV s–1 (≈16‐min charge/discharge time) with cyclability for over 100 000 cycles. Energetics from density functional theory calculations indicate that proton storage occurs at the terminal oxygen sites within the hydrated interlayer. Last, optical micrographs collected during in situ Raman spectroscopy show reversible, multicolor electrochromism, with color changes from pale yellow to blue, purple, and last, orange as a function of proton content. These results highlight the use of selective etching of layered perovskites for the synthesis of metastable transition metal oxide materials and the use of H2W2O7 as an anode material for proton‐based energy storage or electrochromic applications.}, number={1}, journal={ADVANCED ENERGY MATERIALS}, author={Wang, Ruocun and Sun, Yangyunli and Brady, Alexander and Fleischmann, Simon and Eldred, Tim B. and Gao, Wenpei and Wang, Hsiu-Wen and Jiang, De-en and Augustyn, Veronica}, year={2021}, month={Jan} }
 @article{morgan_andie m. o'connell_jansson_peterson_mahle_eldred_gao_parsons_2021, title={Stretchable and Multi-Metal-Organic Framework Fabrics Via High-Yield Rapid Sorption-Vapor Synthesis and Their Application in Chemical Warfare Agent Hydrolysis}, volume={13}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.1c07366}, DOI={10.1021/acsami.1c07366}, abstractNote={Protocols to create metal-organic framework (MOF)/polymer composites for separation, chemical capture, and catalytic applications currently rely on relatively slow solution-based processing to form single MOF composites. Here, we report a rapid, high-yield sorption-vapor method for direct simultaneous growth of single and multiple MOF materials onto untreated flexible and stretchable polymer fibers and films. The synthesis utilizes favorable reactant absorption into polymers coupled with rapid vapor-driven MOF crystallization to form high surface area (>250 m2/gcomposite) composites, including UiO-66-NH2, HKUST-1, and MOF-525 on spandex, nylon, and other fabrics. The resulting composites are robust and maintain their functionality even after stretching. Stretchable MOF fabrics enable rapid solid-state hydrolysis of the highly toxic chemical warfare agent soman and paraoxon-methyl simulant. We show that this approach can readily be scaled by solution spray-coating of MOF precursors and to large area substrates.}, number={26}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Morgan, Sarah E. and Andie M. O'Connell and Jansson, Anton and Peterson, Gregory W. and Mahle, John J. and Eldred, Tim B. and Gao, Wenpei and Parsons, Gregory N.}, year={2021}, month={Jul}, pages={31279–31284} }
 @article{hauwiller_stowe_eldred_mita_collazo_sitar_lebeau_2020, title={Cathodoluminescence of silicon doped aluminum nitride with scanning transmission electron microscopy}, volume={8}, ISSN={["2166-532X"]}, DOI={10.1063/5.0019863}, abstractNote={Here, we apply cathodoluminescence in scanning transmission electron microscopy to infer the influence of dislocation strain fields on the formation of point defect complexes in Si doped AlN. In addition to identifying non-radiative recombination centers, tracking Si related defect emission energies reveals a red-shift at threading dislocations. We discuss these results in the context of multiple Si-vacancy defect complexes that can form and the influence of local strain on their formation energies. By correlating the electronic and structural properties at the nanoscale, cathodoluminescence elucidates the inhomogeneity of defect complexes in Si doped AlN and offers the potential for strain engineering to control the defect energy formation landscape.}, number={9}, journal={APL MATERIALS}, author={Hauwiller, Matthew R. and Stowe, David and Eldred, Timothy B. and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko and LeBeau, James}, year={2020}, month={Sep} }
 @article{eldred_abdelhamid_reynolds_el-masry_lebeau_bedair_2020, title={Observing relaxation in device quality InGaN templates by TEM techniques}, volume={116}, ISSN={["1077-3118"]}, DOI={10.1063/1.5139269}, abstractNote={Device quality InGaN templates are synthesized using the semibulk (SB) approach. The approach maintains the film's 2D growth and avoids the formation of indium-metal inclusions. The strain relaxation processes of the grown InxGa1−xN templates are accompanied by variations in the indium content (x) and lattice parameters (a and c) across the InGaN template's thickness as the residual strain is continuously decreasing. This strain and lattice parameters' variation creates difficulties in applying standard x-ray Diffraction (XRD) and Reciprocal Space mapping (RSM) techniques to estimate the residual strain and the degree of the elastic strain relaxation. We used high-resolution High-angle annular dark-field scanning transmission electron microscopy and Energy-dispersive x-ray spectroscopy (EDS) to monitor the variations of the indium content, lattice parameters, and strain relaxation across the growing InxGa1−xN templates. We show that strain relaxation takes place by V-pit defect formation. Some of these V-pits are refilled by the GaN interlayers in the InxGa1−xN SB templates, while others propagate to the template surface. We present an alternative approach combining photoluminescence (PL) and EDS for estimating the degree of strain relaxation in these InxGa1−xN templates. The values obtained for the degree of relaxation estimated from TEM studies and PL measurements are within reasonable agreement in this study. Device quality InxGa1−xN templates with x ∼ 0.08, with a degree of relaxation higher than 70%, are achieved.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Eldred, Tim B. and Abdelhamid, Mostafa and Reynolds, J. G. and El-Masry, N. A. and LeBeau, James M. and Bedair, S. M.}, year={2020}, month={Mar} }
 @article{dycus_washiyama_eldred_guan_kirste_mita_sitar_collazo_lebeau_2019, title={The role of transient surface morphology on composition control in AlGaN layers and wells}, volume={114}, ISSN={["1077-3118"]}, DOI={10.1063/1.5063933}, abstractNote={The mechanisms governing “compositional pulling” during the growth of AlxGa1−xN wells are investigated. Gallium-rich AlxGa1−xN wells grown on high dislocation density AlN/sapphire templates exhibit asymmetric and diffuse composition profiles, while those grown on low dislocation density native AlN substrates do not. Furthermore, strain in all AlxGa1−xN wells is found to be pseudomorphic, ruling it out as the dominating driving force. Rather, the high threading dislocation density of the AlN template is considered to play the defining role. We propose that a transient surface morphology is introduced during dislocation mediated spiral growth, which, in conjunction with process supersaturation, determines the Ga incorporation. These findings provide insights into compositional pulling in high Ga content AlxGa1−xN grown on AlN and provide a route to grow thicker wells with very abrupt interfaces on native AlN substrates.}, number={3}, journal={APPLIED PHYSICS LETTERS}, author={Dycus, J. Houston and Washiyama, Shun and Eldred, Tim B. and Guan, Yan and Kirste, Ronny and Mita, Seiji and Sitar, Zlatko and Collazo, Ramon and LeBeau, James M.}, year={2019}, month={Jan} }