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1. Approaches to Exploring Spatio-Temporal Surface Dynamics in Nanoparticles with In Situ Transmission Electron Microscopy

   https://doi.org/10.1017/S1431927619015228  

   Lawrence, Ethan L. ; Levin, Barnaby D.A. ; Miller, Benjamin K. ; Crozier, Peter A. ( February 2020 , Microscopy and Microanalysis)

   Abstract Many nanoparticles in fields such as heterogeneous catalysis undergo surface structural fluctuations during chemical reactions, which may control functionality. These dynamic structural changes may be ideally investigated with time-resolved in situ electron microscopy. We have explored approaches for extracting quantitative information from large time-resolved image data sets with a low signal to noise recorded with a direct electron detector on an aberration-corrected transmission electron microscope. We focus on quantitatively characterizing beam-induced dynamic structural rearrangements taking place on the surface of CeO 2 (ceria). A 2D Gaussian fitting procedure is employed to determine the position and occupancy of each atomic column in the nanoparticle with a temporal resolution of 2.5 ms and a spatial precision of 0.25 Å. Local rapid lattice expansions/contractions and atomic migration were revealed to occur on the (100) surface, whereas (111) surfaces were relatively stable throughout the experiment. The application of this methodology to other materials will provide new insights into the behavior of nanoparticle surface reconstructions that were previously inaccessible using other methods, which will have important consequences for the understanding of dynamic structure–property relationships.
2. Disentangling Coexisting Structural Order Through Phase Lock-In Analysis of Atomic-Resolution STEM Data

   https://doi.org/10.1017/S1431927622000125  

   Goodge, Berit H. ; El Baggari, Ismail ; Hong, Seung Sae ; Wang, Zhe ; Schlom, Darrell G. ; Hwang, Harold Y. ; Kourkoutis, Lena F. ( April 2022 , Microscopy and Microanalysis)

   As a real-space technique, atomic-resolution STEM imaging contains both amplitude and geometric phase information about structural order in materials, with the latter encoding important information about local variations and heterogeneities present in crystalline lattices. Such phase information can be extracted using geometric phase analysis (GPA), a method which has generally focused on spatially mapping elastic strain. Here we demonstrate an alternative phase demodulation technique and its application to reveal complex structural phenomena in correlated quantum materials. As with other methods of image phase analysis, the phase lock-in approach can be implemented to extract detailed information about structural order and disorder, including dislocations and compound defects in crystals. Extending the application of this phase analysis to Fourier components that encode periodic modulations of the crystalline lattice, such as superlattice or secondary frequency peaks, we extract the behavior of multiple distinct order parameters within the same image, yielding insights into not only the crystalline heterogeneity but also subtle emergent order parameters such as antipolar displacements. When applied to atomic-resolution images spanning large (~0.5 × 0.5 μ m 2 ) fields of view, this approach enables vivid visualizations of the spatial interplay between various structural orders in novel materials.
3. Advances and Applications of Atomic-Resolution Scanning Transmission Electron Microscopy

   https://doi.org/10.1017/S1431927621012125  

   Liu, Jingyue ( August 2021 , Microscopy and Microanalysis)

   Although scanning transmission electron microscopy (STEM) images of individual heavy atoms were reported 50 years ago, the applications of atomic-resolution STEM imaging became wide spread only after the practical realization of aberration correctors on field-emission STEM/TEM instruments to form sub-Ångstrom electron probes. The innovative designs and advances of electron optical systems, the fundamental understanding of electron–specimen interaction processes, and the advances in detector technology all played a major role in achieving the goal of atomic-resolution STEM imaging of practical materials. It is clear that tremendous advances in computer technology and electronics, image acquisition and processing algorithms, image simulations, and precision machining synergistically made atomic-resolution STEM imaging routinely accessible. It is anticipated that further hardware/software development is needed to achieve three-dimensional atomic-resolution STEM imaging with single-atom chemical sensitivity, even for electron-beam-sensitive materials. Artificial intelligence, machine learning, and big-data science are expected to significantly enhance the impact of STEM and associated techniques on many research fields such as materials science and engineering, quantum and nanoscale science, physics and chemistry, and biology and medicine. This review focuses on advances of STEM imaging from the invention of the field-emission electron gun to the realization of aberration-corrected and monochromated atomic-resolution STEM and its broad applications.
4. Evolution in X-ray analysis from micro to atomic scales in aberration-corrected scanning transmission electron microscopes

   https://doi.org/10.1093/jmicro/dfab026  

   Watanabe, M ; Egerton, R F ( February 2022 , Microscopy)

   Abstract X-ray analysis is one of the most robust approaches to extract quantitative information from various materials and is widely used in various fields ever since Raimond Castaing established procedures to analyze electron-induced X-ray signals for materials characterization ‘70 years ago’. The recent development of aberration-correction technology in a (scanning) transmission electron microscopes (S/TEMs) offers refined electron probes below the Å level, making atomic-resolution X-ray analysis possible. In addition, the latest silicon drift detectors allow complex detector arrangements and new configurational designs to maximize the collection efficiency of X-ray signals, which make it feasible to acquire X-ray signals from single atoms. In this review paper, recent progress and advantages related to S/TEM-based X-ray analysis will be discussed: (i) progress in quantification for materials characterization including the recent applications to light element analysis, (ii) progress in analytical spatial resolution for atomic-resolution analysis and (iii) progress in analytical sensitivity toward single-atom detection and analysis in materials. Both atomic-resolution analysis and single-atom analysis are evaluated theoretically through multislice-based calculation for electron propagation in oriented crystalline specimen in combination with X-ray spectrum simulation.
5. Dual functions of CO ₂ molecular activation and 4f levels as electron transport bridges in erbium single atom composite photocatalysts therefore enhancing visible-light photoactivities

   https://doi.org/10.1039/D1TA02926F  

   Chen, Qiuyu ; Gao, Guoyang ; Zhang, Yanzhou ; li, Yini ; Zhu, Hongyang ; Zhu, Peifen ; Qu, Yang ; Wang, Guofeng ; Qin, Weiping ( July 2021 , Journal of Materials Chemistry A)

   Only when the interfacial charge separation is enhanced and the CO 2 activation is improved, can the heterojunction nanocomposite photocatalyst be brought into full play for the CO 2 reduction reaction (CO 2 RR). Here, Er 3+ single atom composite photocatalysts were successfully constructed based on both the special role of Er 3+ single atoms and the special advantages of the SrTiO 3 :Er 3+ /g-C 3 N 4 heterojunction in the field of photocatalysis for the first time. As we expected, the SrTiO 3 :Er 3+ /g-C 3 N 4 (22.35 and 16.90 μmol g −1 h −1 for CO and CH 4 ) exhibits about 5 times enhancement in visible-light photocatalytic activity compared to pure g-C 3 N 4 (4.60 and 3.40 μmol g −1 h −1 for CO and CH 4 ). In particular, the photocatalytic performance of SrTiO 3 :Er 3+ /g-C 3 N 4 is more than three times higher than that of SrTiO 3 /g-C 3 N 4 . From Er 3+ fluorescence quenching measurements, photoelectrochemical studies, transient PL studies and DFT calculations, it is verified that a small fraction of surface doping of Er 3+ formed Er single-atoms on SrTiO 3 building anmore »energy transfer bridge between the interface of SrTiO 3 and g-C 3 N 4 , resulting in enhanced interfacial charge separation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and adsorption energy calculations demonstrated that the exposed Er single-atoms outside the interface on SrTiO 3 preferentially activate the adsorbed CO 2 , leading to the high photoactivity for the CO 2 RR. A novel enhanced photocatalytic mechanism was proposed, in which Er single-atoms play dual roles of an energy transfer bridge and activating CO 2 to promote charge separation. This provides new insights and feasible routes to develop highly efficient photocatalytic materials by engineering rare-earth single-atom doping.« less