MSE Colloquium: Min Gao, Structure, Bonding and Beyond: Electron Microscopy Studies of Challenging Thin Films, Interfaces, and Nanostructures

Research Scientist, Liquid Crystal Institute, Kent State University

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave
Columbus, OH 43210
United States

Abstract

Electron microscopy is one of the most comprehensive material characterization tools probing structure and chemical bonding at atomic and molecular scale.  However, some “real world” materials impose a variety of challenges on the application of advanced electron microscopy techniques, e.g., extreme irradiation damage and charging, weak scattering, and difficult specimen preparation. In this talk, we present application examples of imaging and spectroscopy in a series of challenging material systems. Our current interest is focused on liquid crystals which exhibit unparalleled irradiation damages. The current dominant nanoscale imaging tool is a replica transmission electron microscopy (TEM) technique, namely freeze fracture TEM, providing a resolution of a few nanometers. In our initial effort, we developed an effective specimen preparation procedure enabling deposition of electron transparent liquid crystal thin films followed by thermal processing and rapid plunge freezing, and a modified cryo-TEM low-dose procedure allowing us to locate and image the areas of interest at a sub-nanometer resolution. The TEM observation of “real” liquid crystals has resulted in the first direct evidence of smectic nanoclusters in a nematic liquid crystal, and makes it possible to apply techniques such as diffraction, spectroscopies, and Z-contrast imaging. We also show examples of high quality electron diffraction from individual carbon nanotubes using nanometer-sized parallel electron beam (which led to unambiguous atomic structural determination of CNTs and atomic resolution diffractive imaging), and extracting interfacial bonding signals at metal/ceramic interfaces using electron energy-loss spectroscopy.

A key challenge and opportunity for electron microscopy is to go beyond structure and chemistry. In a recent effort, we developed a series of techniques integrating in situ scanning electron microscopy (SEM) and optical techniques to achieve comprehensive microstructural, compositional, electrical and optical measurements on the same individual nanostructures. For example, nanomanipulators were used to control optical fiber probes and sharp metal tips, making it possible to assemble and characterize functional optoelectronic “in situ” devices based on individual nanostructures.

Bio

Dr. Min Gao is currently a Research Scientist at Liquid Crystal Institute of Kent State University, and supervisor of the TEM lab and Characterization Facility. Min studied Materials Science at Beijing University of Aeronautics and Astronautics (1990-1994). He got his master degree (1997) and PhD (2000) in Physics from Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences. He also worked in several other electron microscopy labs including those at Max-Planck Institute for Metal Research Stuttgart, University of Illinois at Urbana-Champaign, and The Ohio State University. Before joining Kent State, he was a faculty member at Peking University, China. His experience has been mainly focused on developing advanced electron microscopy techniques and their applications to both hard- and soft-matter materials.