The speaker for this Friday's Seminar is Dr. Honggyu Kim, speaking about Novel Approaches to Quantitative Scanning Transmission Electron Microscopy: Understanding Materials Atom-by-Atom
Numerous emergent materials properties are greatly governed by subtle changes in the structure and chemistry of materials, e.g. dopants, defects, strain, and atomic surface configurations. To establish direct relationships between unique materials properties and structural characteristics, development of analytical tools and techniques with high sensitivity and spatial resolution, down to single-atom precision and picometer-scale detection accuracy, is key to success in the discovery of new functionalities and development of relevant devices. Advances in scanning transmission electron microscopy (STEM), e.g. aberration correction of probe forming lens, have brought about significant enhancements of image resolution and signal-to-noise ratio, allowing for imaging of a single atomic column in a crystal. However, precise quantification of the structure and chemical information from STEM images is often hampered by scan distortion and instabilities of the electron beam and sample position. Novel approaches that acquire and analyze STEM data are thus a necessity to overcome the current limitations and provide access to previously unattainable materials information. In this seminar, I will discuss recent advances in novel quantitative STEM (QSTEM) imaging and analysis techniques and demonstrate how these advances have enabled the direct observation of cation vacancies in
SrTiO3 films grown by molecular beam epitaxy (MBE). The second part of this seminar focuses on the use of QSTEM techniques to elucidate the lattice response to dopants in Sr-doped SmTiO3 films and demonstrate a second-order phase transition with no observable phase separation across a filling-controlled Mott metal-insulator transition. The results from these two case studies open up a new methodology for studying the microscopic mechanisms by which atomic-level structural and chemical modulations control materials properties
Dr. Honggyu Kim is an assistant professor in the Department of Materials Science and Engineering at the University of Florida. He received his Ph.D. in the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. Prior to joining the faculty at the University of Florida in Fall 2019, he was a postdoctoral researcher at the University of California, Santa Barbara. His primary research focuses on the development and application of advanced transmission electron microscopy techniques with the goal of establishing direct relationships between the structure and properties of materials on the atomic scale. His recent research topics include quantitative imaging of epitaxial thin films, atomic-scale defect characterization in functional oxides, symmetry determination of topological materials, and digital image processing techniques.