@article{zhao_ren_sang_liu_wang_dong_ye_2021, title={Higher Nitriding Efficiency in Ultrafine-Grained Iron Processed by Ultrasonic Nanocrystal Surface Modification}, ISSN={["1543-1940"]}, DOI={10.1007/s11661-021-06426-y}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, author={Zhao, Jingyi and Ren, Zhencheng and Sang, Xiahan and Liu, Yang and Wang, G. X. and Dong, Yalin and Ye, Chang}, year={2021}, month={Aug} }
 @article{chen_wang_wiaderek_sang_borkiewicz_chapman_lebeau_lynn_li_2018, title={Super Charge Separation and High Voltage Phase in NaxMnO2}, volume={28}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201805105}, abstractNote={Abstract}, number={50}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Chen, Xi and Wang, Yichao and Wiaderek, Kamila and Sang, Xiahan and Borkiewicz, Olaf and Chapman, Karena and LeBeau, James and Lynn, Jeffrey and Li, Xin}, year={2018}, month={Dec} }
 @article{xu_dycus_sang_lebeau_2016, title={A numerical model for multiple detector energy dispersive X-ray spectroscopy in the transmission electron microscope}, volume={164}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2016.02.004}, abstractNote={Here we report a numerical approach to model a four quadrant energy dispersive X-ray spectrometer in the transmission electron microscope. The model includes detector geometries, specimen position and absorption, shadowing by the holder, and filtering by the Be carrier. We show that this comprehensive model accurately predicts absolute counts and intensity ratios as a function of specimen tilt and position. We directly compare the model to experimental results acquired with a FEI Super-X EDS four quadrant detector. The contribution from each detector to the sum is investigated. The program and source code can be downloaded from https://github.com/subangstrom/superAngle.}, journal={ULTRAMICROSCOPY}, author={Xu, W. and Dycus, J. H. and Sang, X. and LeBeau, J. M.}, year={2016}, month={May}, pages={51–61} }
 @article{sang_lebeau_2016, title={Characterizing the response of a scintillator-based detector to single electrons}, volume={161}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2015.11.008}, abstractNote={Here we report the response of a high angle annular dark field scintillator-based detector to single electrons. We demonstrate that care must be taken when determining the single electron intensity as significant discrepancies can occur when quantifying STEM images with different methods. To account for the detector response, we first image the detector using very low beam currents (∼8fA), and subsequently model the interval between consecutive single electrons events. We find that single electrons striking the detector present a wide distribution of intensities, which we show is not described by a simple function. Further, we present a method to accurately account for the electrons within the incident probe when conducting quantitative imaging. The role detector settings play on determining the single electron intensity is also explored. Finally, we extend our analysis to describe the response of the detector to multiple electron events within the dwell interval of each pixel.}, journal={ULTRAMICROSCOPY}, author={Sang, Xiahan and LeBeau, James M.}, year={2016}, month={Feb}, pages={3–9} }
 @article{spurgeon_du_droubay_devaraj_sang_longo_yan_kotula_shutthanandan_bowden_et al._2016, title={Competing Pathways for Nucleation of the Double Perovskite Structure in the Epitaxial Synthesis of La2MnNiO6}, volume={28}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.6b00829}, abstractNote={Double perovskites of the form R2BB′O6 (where R is a rare earth cation and B and B′ are chemically distinct transition metal cations with half-filled and empty eg orbitals, respectively) are of significant interest for their magnetoelectric properties. La2MnNiO6 is particularly attractive because of its large expected ferromagnetic moment per formula unit (5 μB f.u.–1) and its semiconducting character. If the ideal structure nucleates, superexchange coupling can take place via the B—O—B′ bonds that form, and the moment per formula unit can attain its maximum theoretical value. However, we show that even in the case of layer-by-layer deposition via molecular beam epitaxy, the system can follow multiple reaction pathways that lead to deviations from the double perovskite structure. In particular, we observe a spatially extended phase in which B-site cation disorder occurs, resulting in Mn—O—Mn and Ni—O—Ni antiferromagnetic domains, as well as the formation of quasi-epitaxial, antiferromagnetic NiO nanoscale...}, number={11}, journal={CHEMISTRY OF MATERIALS}, author={Spurgeon, Steven R. and Du, Yingge and Droubay, Timothy and Devaraj, Arun and Sang, Xiahan and Longo, Paolo and Yan, Pengfei and Kotula, Paul G. and Shutthanandan, Vaithiyalingam and Bowden, Mark E. and et al.}, year={2016}, month={Jun}, pages={3814–3822} }
 @article{cheng_yao_sang_hao_zhang_yap_zhu_2016, title={Evolution of Irradiation-Induced Vacancy Defects in Boron Nitride Nanotubes}, volume={12}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201502440}, abstractNote={Irradiation‐induced vacancy defects in multiwalled (MW) boron nitride nanotubes (BNNTs) are investigated via in situ high‐resolution transmission electron microscope operated at 80 kV, with a homogeneous distribution of electron beam intensity. During the irradiation triangle‐shaped vacancy defects are gradually generated in MW BNNTs under a mediate electron current density (30 A cm−2), by knocking the B atoms out. The vacancy defects grow along a well‐defined direction within a wall at the early stage as a result of the curvature induced lattice strain, and then develop wall by wall. The orientation or the growth direction of the vacancy defects can be used to identify the chirality of an individual wall. With increasing electron current density, the shape of the irradiation‐induced vacancy defects changes from regular triangle to irregular polygon.}, number={6}, journal={SMALL}, author={Cheng, Guangming and Yao, Shanshan and Sang, Xiahan and Hao, Boyi and Zhang, Dongyan and Yap, Yoke Khin and Zhu, Yong}, year={2016}, month={Feb}, pages={818–824} }
 @article{dycus_xu_sang_d'alfonso_chen_weyland_allen_findlay_lebeau_2016, title={Influence of experimental conditions on atom column visibility in energy dispersive X-ray spectroscopy}, volume={171}, journal={Ultramicroscopy}, author={Dycus, J. H. and Xu, W. and Sang, X. and D'Alfonso, A. J. and Chen, Z. and Weyland, M. and Allen, L. J. and Findlay, S. D. and LeBeau, J. M.}, year={2016}, pages={1–7} }
 @article{pesic_fengler_larcher_padovani_schenk_grimley_sang_lebeau_slesazeck_schroeder_et al._2016, title={Physical Mechanisms behind the Field-Cycling Behavior of HfO2-Based Ferroelectric Capacitors}, volume={26}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201600590}, abstractNote={Novel hafnium oxide (HfO2)‐based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite‐based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake‐up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake‐up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake‐up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.}, number={25}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Pesic, Milan and Fengler, Franz Paul Gustav and Larcher, Luca and Padovani, Andrea and Schenk, Tony and Grimley, Everett D. and Sang, Xiahan and LeBeau, James M. and Slesazeck, Stefan and Schroeder, Uwe and et al.}, year={2016}, month={Jul}, pages={4601–4612} }
 @article{chen_weyland_sang_xu_dycus_lebeau_d'alfonso_allen_findlay_2016, title={Quantitative atomic resolution elemental mapping via absolute-scale energy dispersive X-ray spectroscopy}, volume={168}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2016.05.008}, abstractNote={Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain. The most likely contributing factors are identified and discussed. Previous predictions that increasing the probe forming aperture helps to suppress the channelling enhancement in the average signal are confirmed experimentally. It is emphasized that simple column-by-column analysis requires a choice of sample thickness that compromises between being thick enough to yield a good signal-to-noise ratio while being thin enough that the overwhelming majority of the EDX signal derives from the column on which the probe is placed, despite strong electron scattering effects.}, journal={ULTRAMICROSCOPY}, author={Chen, Z. and Weyland, M. and Sang, X. and Xu, W. and Dycus, J. H. and LeBeau, J. M. and D'Alfonso, A. J. and Allen, L. J. and Findlay, S. D.}, year={2016}, month={Sep}, pages={7–16} }
 @article{grimley_schenk_sang_pesic_schroeder_mikolajick_lebeau_2016, title={Structural Changes Underlying Field-Cycling Phenomena in Ferroelectric HfO2 Thin Films}, volume={2}, ISSN={["2199-160X"]}, DOI={10.1002/aelm.201600173}, abstractNote={Since 2011, ferroelectric HfO2 has attracted growing interest in both fundamental and application oriented groups. In this material, noteworthy wake‐up and fatigue effects alter the shape of the polarization hysteresis loop during field cycling. Such changes are problematic for application of HfO2 to ferroelectric memories, which require stable polarization hystereses. Herein, electrical and structural techniques are implemented to unveil how cyclic switching changes nanoscale film structure, which modifies the polarization hysteresis. Impedance spectroscopy and scanning transmission electron microscopy identify regions with different dielectric and conductive properties in films at different cycling stages, enabling development of a structural model to explain the wake‐up and fatigue phenomena. The wake‐up regime arises due to changes in bulk and interfacial structuring: the bulk undergoes a phase transformation from monoclinic to orthorhombic grains, and the interfaces show changes in and diminishment of a nonuniform, defect rich, tetragonal HfO2 layer near the electrodes. The evolution of these aspects of structuring contributes to the increase in Pr and the opening of the constricted P–V hysteresis that are known to occur with wake‐up. The onset of the fatigue regime is correlated to an increasing concentration of bulk defects, which are proposed to pin domain walls.}, number={9}, journal={ADVANCED ELECTRONIC MATERIALS}, author={Grimley, Everett D. and Schenk, Tony and Sang, Xiahan and Pesic, Milan and Schroeder, Uwe and Mikolajick, Thomas and LeBeau, James M.}, year={2016}, month={Sep} }
 @inproceedings{zhao_ren_liu_sang_hou_wang_dong_ye_2016, title={Ultrasonic nanocrystal surface modification assisted nitriding: An experimental study}, DOI={10.1115/msec2016-8701}, abstractNote={A powerful surface severe plastic deformation (SSPD) technique, ultrasonic nanocrystal surface modification (UNSM) has been used to treat pure iron to induce surface nanocrystallization. Transmission electron microscopy and surface profiler were used to study the microstructure and surface roughness after UNSM. Results indicate that the surface nanocrystallization with the controllable surface roughness was obtained. After that, gas nitriding of the nanocrystalline and microcrystalline iron was carried out and compared. X-ray diffraction, micro hardness testing and energy dispersive spectroscopy were applied to investigate the phase, micro hardness and distribution of nitrogen atoms in the iron sample after nitriding. It has been found that nitriding efficiency has been significantly improved in UNSM-processed samples than that in the non-processed samples as manifested by higher hardness and higher volume fraction of the nitride phase. With appropriate nanocrystallization, nitriding can occur efficiently at temperature as low as 300 °C.}, booktitle={Proceedings of the ASME 11th International Manufacturing Science and Engineering Conference, 2016, vol 2}, author={Zhao, J. Y. and Ren, Z. C. and Liu, Y. and Sang, X. H. and Hou, X. N. and Wang, G. X. and Dong, Y. L. and Ye, C.}, year={2016} }
 @article{dycus_harris_sang_fancher_findlay_oni_chan_koch_jones_allen_et al._2015, title={Accurate Nanoscale Crystallography in Real-Space Using Scanning Transmission Electron Microscopy}, volume={21}, ISSN={["1435-8115"]}, DOI={10.1017/s1431927615013732}, abstractNote={Abstract}, number={4}, journal={MICROSCOPY AND MICROANALYSIS}, author={Dycus, J. Houston and Harris, Joshua S. and Sang, Xiahan and Fancher, Chris M. and Findlay, Scott D. and Oni, Adedapo A. and Chan, Tsung-ta E. and Koch, Carl C. and Jones, Jacob L. and Allen, Leslie J. and et al.}, year={2015}, month={Aug}, pages={946–952} }
 @article{sang_grimley_niu_irving_lebeau_2015, title={Direct observation of charge mediated lattice distortions in complex oxide solid solutions}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4908124}, abstractNote={Using aberration corrected scanning transmission electron microscopy combined with advanced imaging methods, we directly observe atom column specific, picometer-scale displacements induced by local chemistry in a complex oxide solid solution. Displacements predicted from density functional theory were found to correlate with the observed experimental trends. Further analysis of bonding and charge distribution was used to clarify the mechanisms responsible for the detected structural behavior. By extending the experimental electron microscopy measurements to previously inaccessible length scales, we identified correlated atomic displacements linked to bond differences within the complex oxide structure.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Sang, Xiahan and Grimley, Everett D. and Niu, Changning and Irving, Douglas L. and LeBeau, James M.}, year={2015}, month={Feb} }
 @article{oni_sang_raju_dumpala_broderick_kumar_sinnott_saxena_rajan_lebeau_2015, title={Large area strain analysis using scanning transmission electron microscopy across multiple images}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4905368}, abstractNote={Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Oni, A. A. and Sang, X. and Raju, S. V. and Dumpala, S. and Broderick, S. and Kumar, A. and Sinnott, S. and Saxena, S. and Rajan, K. and LeBeau, J. M.}, year={2015}, month={Jan} }
 @article{sang_grimley_schenk_schroeder_lebeau_2015, title={On the structural origins of ferroelectricity in HfO2 thin films}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4919135}, abstractNote={Here, we present a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films. We apply aberration corrected high-angle annular dark-field scanning transmission electron microscopy to directly determine the underlying lattice type using projected atom positions and measured lattice parameters. Furthermore, we apply nanoscale electron diffraction methods to visualize the crystal symmetry elements. Combined, the experimental results provide unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization, resolving the origin of ferroelectricity in HfO2 thin films.}, number={16}, journal={APPLIED PHYSICS LETTERS}, author={Sang, Xiahan and Grimley, Everett D. and Schenk, Tony and Schroeder, Uwe and LeBeau, James M.}, year={2015}, month={Apr} }
 @article{ye_liu_sang_ren_zhao_hou_dong_2015, title={Solid state amorphization of nanocrystalline nickel by cryogenic laser shock peening}, volume={118}, ISSN={["1089-7550"]}, DOI={10.1063/1.4932142}, abstractNote={In this study, complete solid state amorphization in nanocrystalline nickel has been achieved through cryogenic laser shock peening (CLSP). High resolution transmission electron microscopy has revealed the complete amorphous structure of the sample after CLSP processing. A molecular dynamic model has been used to investigate material behavior during the shock loading and the effects of nanoscale grain boundaries on the amorphization process. It has been found that the initial nanoscale grain boundaries increase the initial Gibbs free energy before plastic deformation and also serve as dislocation emission sources during plastic deformation to contribute to defect density increase, leading to the amorphization of pure nanocrystalline nickel.}, number={13}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ye, Chang and Liu, Yang and Sang, Xiahan and Ren, Zhencheng and Zhao, Jingyi and Hou, Xiaoning and Dong, Yalin}, year={2015}, month={Oct} }
 @article{niu_zaddach_oni_sang_hurt_lebeau_koch_irving_2015, title={Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo}, volume={106}, ISSN={["1077-3118"]}, DOI={10.1063/1.4918996}, abstractNote={Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.}, number={16}, journal={APPLIED PHYSICS LETTERS}, author={Niu, C. and Zaddach, A. J. and Oni, A. A. and Sang, X. and Hurt, J. W., III and LeBeau, J. M. and Koch, C. C. and Irving, D. L.}, year={2015}, month={Apr} }
 @article{sang_oni_lebeau_2014, title={Atom Column Indexing: Atomic Resolution Image Analysis Through a Matrix Representation}, volume={20}, ISSN={["1435-8115"]}, DOI={10.1017/s1431927614013506}, abstractNote={Abstract}, number={6}, journal={MICROSCOPY AND MICROANALYSIS}, author={Sang, Xiahan and Oni, Adedapo A. and LeBeau, James M.}, year={2014}, month={Dec}, pages={1764–1771} }
 @article{lomenzo_zhao_takmeel_moghaddam_nishida_nelson_fancher_grimley_sang_lebeau_et al._2014, title={Ferroelectric phenomena in Si-doped HfO2 thin films with TiN and Ir electrodes}, volume={32}, number={3}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Lomenzo, P. D. and Zhao, P. and Takmeel, Q. and Moghaddam, S. and Nishida, T. and Nelson, M. and Fancher, C. M. and Grimley, E. D. and Sang, X. H. and LeBeau, J. M. and et al.}, year={2014} }
 @article{sang_lebeau_2014, title={Revolving scanning transmission electron microscopy: Correcting sample drift distortion without prior knowledge}, volume={138}, ISSN={["1879-2723"]}, DOI={10.1016/j.ultramic.2013.12.004}, abstractNote={We report the development of revolving scanning transmission electron microscopy--RevSTEM--a technique that enables characterization and removal of sample drift distortion from atomic resolution images without the need for a priori crystal structure information. To measure and correct the distortion, we acquire an image series while rotating the scan coordinate system between successive frames. Through theory and experiment, we show that the revolving image series captures the information necessary to analyze sample drift rate and direction. At atomic resolution, we quantify the image distortion using the projective standard deviation, a rapid, real-space method to directly measure lattice vector angles. By fitting these angles to a physical model, we show that the refined drift parameters provide the input needed to correct distortion across the series. We demonstrate that RevSTEM simultaneously removes the need for a priori structure information to correct distortion, leads to a dramatically improved signal-to-noise ratio, and enables picometer precision and accuracy regardless of drift rate.}, journal={ULTRAMICROSCOPY}, author={Sang, Xiahan and LeBeau, James M.}, year={2014}, month={Mar}, pages={28–35} }