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Atomic scale defects in advanced materials: How we “see” and understand them

Speaker

Prof. Jinwoo Hwang, Department of Materials Science and Engineering, The Ohio State University

Education

- Ph.D., University of Wisconsin Madison, Materials Science and Engineering, June 2011, (Advisor: Paul M. Voyles)

- M.S., University of Pennsylvania, Materials Science and Engineering, May 2005, (Advisor: David E. Luzzi)

- B.S., Hongik University, Seoul, Korea, Materials Science and Engineering, August 2002

Professional Experience

- 2020 - present, Associate Professor, Materials Science Engineering, The Ohio State University

- 2014 - 2020, Assistant Professor, Materials Science Engineering, The Ohio State University

- 2011 - 2014, Postdoctoral Research Fellow, Materials Department, University of California Santa Barbara (Advisor: Susanne Stemmer)

| Date | Friday, December 10th, 2021

| Time | 10:30 ~ 

| Venue | 33동 223호 (동부세미나실)* 비대면 참석 원칙

            줌링크:  https://snu-ac-kr.zoom.us/j/84442708915

Abstract

Materials’ important properties are often dictated by atomic-to-nanoscale defects and therefore it is crucial to understand and control them. We advance quantitative scanning transmission electron microscopy (STEM) to determine the exact structure, chemistry, and functionality of defects in materials with unprecedented details. This talk will discuss how we precisely investigate the atomic scale defects and structural heterogeneity in different materials systems, and correlate the information to computational simulation and theory to establish the exact structure-property relationships at the atomic-to-nanometer scale. Four different materials systems will be discussed. (1) Ultra-wide bandgap (UWBG) gallium oxide materials and interfaces: Ga2O3 has been recently gaining significant attention due to its unique properties including the large band gap (~ 5.8 eV) and high breakdown voltage, which provide exciting new opportunities for development of new UWBG materials and devices for extreme environment. We directly observe the formation of point defects and their complexes that relate to the trap states which are critical to understand. (2) Antiferromagnetic (AF) insulator interfaces: AF insulators offer greater benefits such as faster switching speed and low magnetic damping, as compared to the ferromagnetic counterparts, for potential future spintronic applications. We study new ways of controlling the lattice distortion with picometer precision, which we quantify using high precision STEM, at AF insulator interfaces and correlate the information to density functional theory to understand the changes in magnetic behaviors of the films. (3) Structural heterogeneity in metallic glasses (MGs): Structure-property relationships in amorphous materials can be difficult to establish due to the challenges in determining and understanding the atomic structure and defects in those materials. We study the unique mechanical properties of MGs, such as shear banding and localization, and find their origins in nanoscale heterogeneity in their structure that we measure using electron nanodiffraction. We correlate the information to what has been known as “flow defects” in MGs that dictate their mechanical behavior. (4) Debye-Waller thermometry in STEM: Interfaces impose extra resistance to thermal conduction, or thermal interface resistance (TIR). Understanding TIR has been one of the most challenging aspects in thermal engineering of electronic and functional devices. We develop a new atomic scale thermometry based on quantitative understanding of electron scattering to measure precise temperature of materials at the atomic scale. Precise quantification of temperature drop at the interface provides TIR information with unprecedented precision and resolution, which we use to advance novel interface designs to reduce TIR at semiconductor and oxide interfaces. 

| Host | Prof. Eun Soo Park (02-880-1713)