@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{smith_huang_gao_zhang_chi_2023, title={Atomic Resolution Cryogenic 4D-STEM Imaging via Robust Distortion Correction}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.2c12777}, abstractNote={Cryogenic four-dimensional scanning transmission electron microscopy (4D-STEM) imaging is a useful technique for studying quantum materials and their interfaces by simultaneously probing charge, lattice, spin, and chemistry on the atomic scale with the sample held at temperatures ranging from room to cryogenic. However, its applications are currently limited by the instabilities of cryo-stages and electronics. To overcome this challenge, we develop an algorithm to effectively correct the complex distortions present in atomic resolution cryogenic 4D-STEM data sets. This method uses nonrigid registration to identify localized distortions in a 4D-STEM and relate them to an undistorted experimental STEM image, followed by a series of affine transformations for distortion corrections. This method allows a minimum loss of information in both reciprocal and real spaces, enabling the reconstruction of sample information from 4D-STEM data sets. This method is computationally cheap, fast, and applicable for on-the-fly data analysis in future in situ cryogenic 4D-STEM experiments.}, journal={ACS NANO}, author={Smith, Jacob and Huang, Zhennan and Gao, Wenpei and Zhang, Guannan and Chi, Miaofang}, year={2023}, month={Jun} }
 @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{witharamage_christudasjustus_smith_gao_gupta_2022, title={Corrosion behavior of an in situ consolidated nanocrystalline Al-V alloy}, volume={6}, ISSN={["2397-2106"]}, url={https://doi.org/10.1038/s41529-022-00225-5}, DOI={10.1038/s41529-022-00225-5}, abstractNote={Abstract Supersaturated solid solutions of Al and corrosion-resistant alloying elements (M: V, Mo, Cr, Ti, Nb), produced by non-equilibrium processing techniques, have been reported to exhibit high corrosion resistance and strength. The corrosion mechanism for such improved corrosion performance has not been well understood. We present a fundamental understanding of the role of V in corrosion of an Al-V alloy, which will provide a theoretical background for developing corrosion-resistant Al alloys. High-energy ball milling of the elemental powder of Al and V produced an in situ consolidated Al-V alloy, which exhibited high solid solubility of V. The corrosion resistance of Al-V alloy was significantly higher than that of pure Al, which was attributed to the (1) enrichment of V at the passive film/substrate interface, (2) incorporation of V into the passive film, and (3) deposition of V on the iron-containing cathodic particles and therefore, retardation of cathodic reaction.}, number={1}, journal={NPJ MATERIALS DEGRADATION}, author={Witharamage, C. S. and Christudasjustus, J. and Smith, J. and Gao, W. and Gupta, R. K.}, year={2022}, month={Feb} }
 @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{narayan_joshi_smith_gao_weber_narayan_2022, title={Q-carbon as a new radiation-resistant material}, volume={186}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2021.10.006}, abstractNote={We have discovered that Q-carbon is extremely resistant to radiation damage under ion irradiations involving extreme atomic displacements and electronic excitations. Using 5 MeV Au + ions, the Q-carbon films on sapphire substrates were irradiated in the dose range 3.3–10 dpa (displacements-per-atom). After the ion irradiations, detailed studies on the atomic structure and bonding characteristics showed that atomic structure and bonding characteristics of amorphous Q-carbon remained essentially unchanged to 10 dpa of radiation damage, which is equivalent to over twenty years of neutron damage in a conventional reactor. There was an ion-beam mixed layer below the Q-carbon layer, whose thickness increased from 5 nm to 10 nm, as the dose increased from 3.3 to 10 dpa. This layer was found to be mostly amorphous with a mixture Al2O3 and Al4C3. This layer, formed as a result of enhanced forward scattering and ballistic ion beam mixing, exhibited composition consistent with detailed TRIM calculations. We also found that nanodiamonds (3 nm average size) embedded in Q-carbon grew to about 60 nm after 6.6 dpa and shrank to about 40 nm after 10 dpa. We discuss the mechanism for the growth and shrinkage of metastable phase of diamond under nonequilibrium ion irradiations.}, journal={CARBON}, author={Narayan, J. and Joshi, P. and Smith, J. and Gao, W. and Weber, W. J. and Narayan, R. J.}, year={2022}, month={Jan}, pages={253–261} }
 @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} }