Join the Department of Materials Science and Engineering for light refreshments and a presentation by Honggyu Kim, post doctoral scholar in the materials department at the University of California, Santa Barbara.
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 signalto-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 (e.g. variable angle, high-angle annular dark-field imaging and rigid image registration) 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.