3 WPI Research Center, AIMR, Tohoku University, Sendai, 980-8577, Japa 2 Nanostructures Res. Lab., Japan Fine Ceramics Center, Nagoya, 456-8587, Japan 1 Institute of Engineering Innovation, The University of Tokyo, Tokyo, 113-8656, Japan 18 Abstract Breakthrough Developments in Atomic Resolution Electron Microscopy and Its Applications for Materials Science Yuichi Ikuhara NIMS Award Winning LectureThe advent of aberration-corrected scanning transmission electron microscopy (STEM) has made it possible to analyze the atomic structure of interfaces in materials, as well as individual atomic columns, not only by identifying their positions and elements but also by assessing local composition and electronic states. Additionally, the ability to precisely apply stress and control the electron beam within the electron microscope allows for the direct high-resolution observation of dynamic phenomena such as fracture, deformation, and diffusion in materials. In this presentation, I will introduce the latest observation techniques applied to various ceramic materials and discuss the insights gained for material design guidelines and the elucidation of functional mechanisms. Ceramic materials are composed of light elements such as oxygen and nitrogen, making the direct observation of light elements essential. However, conventional annular dark field ADF-STEM methods have made it difficult to observe light elements. To address this, our group developed the annular bright field (ABF)-STEM method, which captures electrons scattered at low angles, enabling the direct observation of light elements in materials. Using this method, we successfully observed lithium atoms in lithium-ion battery materials, which are gaining attention as energy and environmental materials, as well as hydrogen atom columns in hydrides. Moreover, we collaborated with the University of Tokyo and JEOL to enhance the resolution of STEM instruments, achieving a spatial resolution of 40.5 pm in 2017, which remains the world record for STEM spatial resolution. In terms of material applications, in 2005, the University of Tokyo was the first in Japan to equip an existing STEM instrument with an aberration corrector, applying it to structural analysis of various materials’ interfaces, grain boundaries, and dislocations. For example, the addition of trace amounts of various dopants to ceramic materials can significantly alter their mechanical and electrical properties. This method has been used to elucidate the causes and mechanisms behind such property changes. By examining ceramic interfaces with different dopants, we identified dopant segregation sites and, through the combined use of atomic-resolution EDS and EELS, were able to determine the specific elements that had segregated and measure their electronic states. We quantitatively clarified the mechanisms of these dopants by comparing the observation results with first-principles calculations. Further applications of aberration-corrected STEM include identifying the atomic positions of light elements in inorganic materials, understanding the core structures of dislocations and lattice defects, and discovering one-dimensional ordered crystals formed at grain boundary triple junctions—clarifying previously elusive material phenomena.
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