Scanning transmission electron microscopy (STEM) is one of standard tools for characterizing local crystal structures. Here we review a few decisive factors to perform crystal structure analysis using STEM, particularly for measuring atomic column positions with picometer precision. Experimental techniques for acquiring high signal-to-noise ratio images without image distortions are presented. Although the incoherent imaging approximation well represents annular dark-field imaging, dynamical diffraction effect and specimen misalignment could disturb its application with an accuracy of picometer level.
It is extremely important to measure at nanometer scale the lattice distortion at a defect in crystal or an intentionally introduced strain to control electronic and/or mechanical functionality. When we observe a crystal sample along a zone axis using a transmission electron microscope (TEM), a lattice image or atomic column image can be obtained. In addition, it recently becomes a routine work to observe atomic column image using a scanning transmission electron microscope (STEM), where we can simultaneously obtain spectroscopic information. Several methods to measure the lattice strain at an order of 10-2 have been developed based on the images obtained with high-resolution electron microscopes. In this report we investigate two complementary techniques to measure the lattice strain: one is Peak-Pairs Analysis (PPA) that measures local lattice expansion/contraction by analyzing equivalent peak positions, and the other is Geometric Phase Analysis (GPA) that decomposes a high-resolution image to a set of lattice fringes using Fourier transform, and measures a faint displacement of the lattice fringes using the geometrical phase. The concept of geometrical phase is also used to measure lattice strain from Dark-Field Electron Holography or STEM Moiré Analysis.
Epitaxial heterostructures based on perovskite transition-metal oxides (ABO3) exhibit their variety of functional properties not seen in the bulk materials. While oxygen octahedral distortions in the perovskite oxide heterostructures have close links to the functional properties, atomistic understanding of the oxygen octahedral distortions has been a challenged as it requires precise measurements of the oxygen atomic positions. High-angle annular dark-field and annular bright-field imaging in aberration-corrected scanning transmission electron microscopy (STEM) allows to visualize both cation and oxygen atomic positions in the oxide heterointerfaces at atomic level. Moreover, the fast multiple-image acquisition and drift correlation techniques provide to the structural images with minimized image distortion. The result revealed that the displacement of the oxygen atom at the heterointerface strongly correlated to the functional properties of the epitaxial films.
Scanning transmission electron microscopy is a powerful technique for analyzing materials at the atomic level. High-tech materials require design at the nanoscale level to optimize their properties. Analyzing changes in atomic positions near surface, heterointerfaces, and other crystalline defects with picometer-level precision are crucial to understand the relationships between structures and properties to be probed in unprecedented detail. In this study, we measured cation displacements at the (010) surface of Li-ion battery cathode material LiFePO4 and within multiphase nanodomains of a strained BaTiO3 film.
The advancement in volume imaging using scanning electron microscopy has made three dimensional ultrastructural analyses of biological specimens more widely available in life science. On the other hand, problems of artifacts are caused in scanning electron microscopic observation by charging and sample damages of biological specimens with low conductivity and contrast. In order to overcome these problems, development and modification of sample preparation methods and electron microscopic devices which reduce charging in microscopic chambers have been reported. These advancements led to compensation of charging, reduction of sample damages during sectioning and observation, and acquisition of data at high signal-to-noise-ratio and/or resolution. Further development of these technologies would improve three dimensional ultrastructural analyses of biological specimens at better scale, quality and throughput, and pave the way to the deeper understanding of structural information which supports biological functions in living organisms.
Phase-shifting electron holography (PS-EH) is one of the phase imaging TEM techniques and provides quantitative and precise evaluation of electromagnetic fields in functional materials. Here, we applied this technique to visualize dopant distribution (1016/1017/1018/1019 atoms/cm3) in a n-type GaN model sample. The all layers were clearly observed with enough signals. We also succeeded in observing significant changes of electric potential, field and charge distributions around GaAs p-n junctions by biasing PS-EH. In addition, we applied compressive sensing technology to the PS-EH and found that a signal/noise ratio in hologram improved drastically, which leads to 500 times higher speed observation using in situ PS-EH. In this paper, the above results are described.
Lamellar granules (LGs), which are fused to the cellular membrane and release their contents to intracellular spaces, are thought to play crucial roles in the skin barrier formation and desquamation. Although LGs have been observed as oval-shaped vesicles or vesicular tubular structures on electron micrographs, the overall structures of LGs in the epidermis are unclear due to the technical limitations of the previously applied microscopy techniques. In this study, we aimed to elucidate how the structures of LGs change in normal human skin by using focused ion beam scanning microscopy (FIB-SEM). The 3D images showed that LGs fused with the cellular membrane in the most superficial granular layer. LGs in the second granular layer was not only localized in the cytoplasm but also secreted into the intercellular space and structure of LGs was reticular at the cell surface. In contrast, within the SG3 layer, LGs resided in the cytoplasm as vesicles. Furthermore, the trans-Golgi network which was well developed, spread into the cytoplasm with branched tubular structures and connected to LGs.
We have developed a unique methodology and a new hardware/software-integrated system for in-situ straining and electron tomography (ET) experiments. The central software of the system controls a straining-and-tomography specimen holder, imaging devices and the specimen stage of a transmission electron microscope (TEM) in an integrated manner. Using the system, one can perform in-situ time-resolved three-dimensional (3D) studies that explore in real-time and at sub-microscopic levels the internal behavior of materials subjected to external stresses. 3D visualization of a Pb–Sn solder alloy thin foil’s deformation dynamics by iterative step-wise stress loading and tilt-series data sets acquisition is introduced as an application of the system.