Topic: Probing the Atomic Scale Structure and Dynamic Behaviors of Materials by Transmission Electron Microscopy

Speaker: Prof. Xiaoqing Pan
　　　　　Department of Chemical Engineering and Materials Science
　　　　　Department of Physics and Astronomy
　　　　　UC Irvine Materials Research Institute (IMRI)
　　　　　University of California – Irvine, Irvine, CA

Time: 10:00-11:30, (Wed.) May 2^nd, 2018

Venue: Room 403，Shi Changxu Building, IMR CAS

Abstract:

Using monochromated, aberration-corrected transmission electron microscope (TEM) one can determine the 3D structure, composition, and electronic properties of nanostructures with the sub-angstrom resolution.  The recent development of in situ TEM techniques allows to observe the atomic scale dynamic behaviors of materials under applied fields, stress, or changing atmosphere. In this talk, I will first present our work on the development of TEM techniques for imaging electric polarization and probing the nucleation and growth of ferroelectric domains and the interaction between domain walls and crystal defects during electric polarization switching. It was found that the charged domain walls can be created or erased by applying a bias, and the local resistance of domain wall strongly depends on the characteristics of charges, which opens up a possibility to develop ultrahigh-density information storage devices. I will then present our studies on the structures and dynamic evolution of catalysts under realistic conditions with atomic precision through a MEMS-based, electron-transparent closed cell with a heating stage. For example, under reducing conditions, certain reducible supports (such as titanium oxides) migrate onto supported metallic particles and create strong metal−support states that drastically change the reactivity of the systems. I will also show the surface reconstruction and shape evolution of metal nanoparticles induced by adsorption of gaseous molecules, and formation of the core-shell platinum-metal nanoparticles in TEM gas cell, which show a catalytic performance in the oxygen reduction reaction superior to that of pure Pt nanoparticles.