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    High-resolution electron microscopy for heterogeneous catalysis research
    Yong Zhu(朱勇), Mingquan Xu(许名权), Wu Zhou(周武)
    Chin. Phys. B, 2018, 27 (5): 056804.   DOI: 10.1088/1674-1056/27/5/056804
    Abstract852)   HTML    PDF (6488KB)(375)      
    Heterogeneous catalysts are the most important catalysts in industrial reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the atomic scale, possess activities that are closely connected to their structural characteristics such as particle size, surface morphology, and three-dimensional topography. Recently, the development of advanced analytical transmission electron microscopy (TEM) techniques, especially quantitative high-angle annular dark-field (HAADF) imaging and high-energy resolution spectroscopy analysis in scanning transmission electron microscopy (STEM) at the atomic scale, strengthens the power of (S)TEM in analyzing the structural/chemical information of heterogeneous catalysts. Three-dimensional reconstruction from two-dimensional projected images and the real-time recording of structural evolution during catalytic reactions using in-situ (S)TEM methods further broaden the scope of (S)TEM observation. The atomic-scale structural information obtained from high-resolution (S)TEM has proven to be of significance for better understanding and designing of new catalysts with enhanced performance.
    Structural biology revolution led by technical breakthroughs in cryo-electron microscopy
    Chang-Cheng Yin(尹长城)
    Chin. Phys. B, 2018, 27 (5): 058703.   DOI: 10.1088/1674-1056/27/5/058703
    Abstract886)   HTML    PDF (3716KB)(400)      
    Recent technical breakthroughs in cryo-electron microscopy (cryo-EM) revolutionized structural biology, which led to the 2017 Nobel Prize in chemistry being awarded to three scientists, Jacques Dubochet, Joachim Frank, and Richard Henderson, who made groundbreaking contributions to the development of cryo-EM. In this review, I will give a comprehensive review of the developmental history of cryo-EM, the technical aspects of the breakthrough in cryo-EM leading to the structural biology revolution, including electron microscopy, image recording devices and image processing algorithms, and the major scientific achievements by Chinese researchers employing cryo-EM, covering protein complexes involved in or related to gene expression and regulation, protein synthesis and degradation, membrane proteins, immunity, and viruses. Finally, I will give a perspective outlook on the development of cryo-EM in the future.
    Chemical structure of grain-boundary layer in SrTiO3 and its segregation-induced transition: A continuum interface approach
    Hui Gu(顾辉)
    Chin. Phys. B, 2018, 27 (6): 060503.   DOI: 10.1088/1674-1056/27/6/060503
    Abstract878)   HTML    PDF (1866KB)(466)      

    Grain-boundary (GB) structures are commonly imaged as discrete atomic columns, yet the chemical modifications are gradual and extend into the adjacent lattices, notably the space charge, hence the two-dimensional defects may also be treated as continuum changes to extended interfacial structure. This review presents a spatially-resolved analysis by electron energy-loss spectroscopy of the GB chemical structures in a series of SrTiO3 bicrystals and a ceramic, using analytical electron microscopy of the pre-Cs-correction era. It has identified and separated a transient layer at the model Σ5 grain-boundaries (GBs) with characteristic chemical bonding, extending the continuum interfacial approach to redefine the GB chemical structure. This GB layer has evolved under segregation of iron dopant, starting from subtle changes in local bonds until a clear transition into a distinctive GB chemistry with substantially increased titanium concentration confined within the GB layer in 3-unit cells, heavily strained, and with less strontium. Similar segregated GB layer turns into a titania-based amorphous film in SrTiO3 ceramic, hence reaching a more stable chemical structure in equilibrium with the intergranular Ti2O3 glass also. Space charge was not found by acceptor doping in both the strained Σ5 and amorphous GBs in SrTiO3 owing to the native transient nature of the GB layer that facilitates the transitions induced by Fe segregation into novel chemical structures subject to local and global equilibria. These GB transitions may add a new dimension into the structure-property relationship of the electronic materials.

    Orienting the future of bio-macromolecular electron microscopy
    Fei Sun(孙飞)
    Chin. Phys. B, 2018, 27 (6): 063601.   DOI: 10.1088/1674-1056/27/6/063601
    Abstract973)   HTML    PDF (1236KB)(325)      

    With 40 years of development, bio-macromolecule cryo-electron microscopy (cryo-EM) has completed its revolution in terms of resolution and currently plays a highly important role in structural biology study. According to different specimen states, cryo-EM involves three specific techniques:single-particle analysis (SPA), electron tomography and sub-tomogram averaging, and electron diffraction. None of these three techniques have realized their full potential for solving the structures of bio-macromolecules and therefore need additional development. In this review, the current existing bottlenecks of cryo-EM SPA are discussed with theoretical analysis, which include the air-water interface during specimen cryo-vitrification, bio-macromolecular conformational heterogeneity, focus gradient within thick specimens, and electron radiation damage. Furthermore, potential solutions of these bottlenecks worthy of further investigation are proposed and discussed.

    Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries
    Yu-Xin Tong(仝毓昕), Qing-Hua Zhang(张庆华), Lin Gu(谷林)
    Chin. Phys. B, 2018, 27 (6): 066107.   DOI: 10.1088/1674-1056/27/6/066107
    Abstract891)   HTML    PDF (8102KB)(568)      

    Scanning transmission electron microscopy (STEM) has been shown as powerful tools for material characterization, especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field (HAADF) and annular bright field (ABF) imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomic-level structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries (LIBs). The future prospects of the STEM are also discussed.

    Towards dynamic structure of biological complexes at atomic resolution by cryo-EM
    Kai Zhang(张凯)
    Chin. Phys. B, 2018, 27 (6): 066801.   DOI: 10.1088/1674-1056/27/6/066801
    Abstract560)   HTML    PDF (344KB)(258)      

    Cryo-electron microscopy makes use of transmission electron microscopy to image vitrified biological samples and reconstruct their three-dimensional structures from two-dimensional projections via computational approaches. After over 40 years of development, this technique is now reaching its zenith and reforming the research paradigm of modern structural biology. It has been gradually taking over X-ray crystallography as the mainstream method. In this review, we briefly introduce the history of cryo-EM, recent technical development and its potential power to reveal dynamic structures. The technical barriers and possible approaches to tackle the upcoming challenges are discussed.

    Lorentz transmission electron microscopy studies on topological magnetic domains
    Li-Cong Peng(彭丽聪), Ying Zhang(张颖), Shu-Lan Zuo(左淑兰), Min He(何敏), Jian-Wang Cai(蔡建旺), Shou-Guo Wang(王守国), Hong-Xiang Wei(魏红祥), Jian-Qi Li(李建奇), Tong-Yun Zhao(赵同云), Bao-Gen Shen(沈保根)
    Chin. Phys. B, 2018, 27 (6): 066802.   DOI: 10.1088/1674-1056/27/6/066802
    Abstract719)   HTML    PDF (16356KB)(391)      

    Lorentz transmission electron microscopy (TEM) is a powerful tool to study the crystal structures and magnetic domain structures in correlation with novel physical properties. Nanometric topological magnetic configurations such as vortices, bubbles, and skyrmions have received enormous attention from the viewpoint of both fundamental science and potential applications in magnetic logic and memory devices, in which understanding the physical properties of magnetic nanodomains is essential. In this review article, several magnetic imaging methods in Lorentz TEM including the Fresnel and Foucault modes, electron holography, and differential phase contrast (DPC) techniques are discussed, where the novel properties of topological magnetic domains are well addressed. In addition, in situ Lorentz TEM demonstrates that the topological domains can be efficiently manipulated by electric currents, magnetic fields, and temperatures, exhibiting novel phenomena under external fields, which advances the development of topological nanodomain-based spintronics.

    Cryo-ET bridges the gap between cell biology and structural biophysics
    Xiao-Fang Cheng(程小芳), Rui Wang(王睿), Qing-Tao Shen(沈庆涛)
    Chin. Phys. B, 2018, 27 (6): 066803.   DOI: 10.1088/1674-1056/27/6/066803
    Abstract564)   HTML    PDF (3566KB)(297)      

    Cryo-electron tomography (cryo-ET) is a cutting-edge technology providing three-dimensional in situ ultra-structural information of macromolecular machineries, organelles, and eukaryotic cells in their native environment at an unprecedented level of detail. Cryo-ET enables the direct observation of dynamic macromolecular architectures of bio-samples in their naturally occurring physiological state, without any harmful artifacts introduced by heavy metal staining, dehydration, and chemical fixation, which occur in traditional transmission electron microscopy. Over decades, cryo-ET has been providing insights into numerous aspects of cellular biology by revealing the pristinely preserved ultra-structures of different cellular components comprising the crowded and complex environment of the cell, thus, bridging the gap between cellular biology and structural biophysics. In this paper, we review the fundamentals of this technique, its recent advances in optics, detection devices, and computational algorithms. The enhancement of our understanding of structural cellular biology by combining these improvements, when integrated with other methods, such as cryo-focused ion beam milling, correlative light and electron microscopy, is discussed via a few examples from research groups worldwide. We also believe that cryo-ET applications in cell biology continue to provide fundamental insights into the field, revolutionizing structural biology itself.

    Quantitative measurement of magnetic parameters by electron magnetic chiral dichroism
    Dong-Sheng Song(宋东升), Zi-Qiang Wang(王自强), Xiao-Yan Zhong(钟虓龑), Jing Zhu(朱静)
    Chin. Phys. B, 2018, 27 (5): 056801.   DOI: 10.1088/1674-1056/27/5/056801
    Abstract748)   HTML    PDF (3948KB)(288)      
    Electron magnetic circular dichroism opens a new door to explore magnetic properties by transmitted electrons in the transmission electron microscope. However, obtaining quantitative magnetic parameters, such as spin and orbital magnetic moment with element-specificity, goes a long way along with the development and improvement of this technique both in theoretical and experimental aspects. In this review, we will give a detailed description of the quantitative electron magnetic circular dichroism (EMCD) technique to measure magnetic parameters with spin-specificity, element-specificity, site-specificity, and orbital-spin-specificity. The discussion completely contains the procedures from raw experimental data acquisition to final magnetic parameters, together with the related custom code we have developed.
    Computing methods for icosahedral and symmetry-mismatch reconstruction of viruses by cryo-electron microscopy
    Bin Zhu(朱彬), Lingpeng Cheng(程凌鹏), Hongrong Liu(刘红荣)
    Chin. Phys. B, 2018, 27 (5): 056802.   DOI: 10.1088/1674-1056/27/5/056802
    Abstract702)   HTML    PDF (4912KB)(378)      
    Three-dimensional (3D) reconstruction of icosahedral viruses has played a crucial role in the development of cryo-electron microscopy single-particle reconstruction, with many cryo-electron microscopy techniques first established for structural studies of icosahedral viruses, owing to their high symmetry and large mass. This review summarizes the computational methods for icosahedral and symmetry-mismatch reconstruction of viruses, as well as the likely challenges and bottlenecks in virus reconstruction, such as symmetry mismatch reconstruction, contrast transformation function (CTF) correction, and particle distortion.
    Quantitative HRTEM and its application in the study of oxide materials
    Chun-Lin Jia(贾春林), Shao-Bo Mi(米少波), Lei Jin(金磊)
    Chin. Phys. B, 2018, 27 (5): 056803.   DOI: 10.1088/1674-1056/27/5/056803
    Abstract783)   HTML    PDF (7645KB)(306)      
    On the basis of a state-of-the-art aberration-corrected transmission electron microscope, the spherical aberration coefficient CS of the objective lens can be tuned to either a positive or a negative value. The use of a negative value of CS combined with an overfocus setting of the objective lens leads to the development of the negative CS imaging (NCSI) technique. Images obtained using the NCSI technique show superior contrast and signal intensity at atomic column positions than the corresponding positive CS images, especially for weakly scattering oxygen columns that are in close proximity to strongly scattering cation columns in oxides. Based on the images obtained under the NCSI condition, quantification of the image contrast allows measurements of the atom positions with a precision of a few picometers and the local chemistry on atomic scale. In the present review, we discuss firstly the benefits of the NCSI technique in studies of oxide materials, and then show a procedure for quantitative analysis of the image based on the absolute value of contrast. In the last part, examples are given for the application of the quantitative high-resolution transmission electron microscopy (HRTEM) to the study of electric dipoles of oxide ferroelectrics and atomic-scale chemistry of interfaces.