MSE Colloquium: Nasim Alem, Defect phenomena in nanostructures: An ultrahigh resolution aberration-corrected electron microscopy study

Abstract

Defects and interfaces can have a profound effect on the macroscale physical and chemical properties of nanostructures through modifying their local atomic and electronic structure. While defects and interfaces have been a well-studied subject for decades, we know little about their local atomic and chemical structure, sub-Angstrom structural distortions within their vicinity, and their stability and transition dynamics under extreme conditions. The past decade has seen incredible progress in the ability to image and manipulate the atomic and chemical structure of nanomaterials with the development of aberration-corrected scanning/transmission electron microscopy (S/TEM). Using ultra-high resolution aberration-corrected S/TEM imaging and spectroscopy, this presentation will focus on our recent efforts on probing the atomic and chemical structure of nanomaterials and the sub-Angstrom structural distortions and relaxation effects that occurs around the defects, dopants, domain walls and interfaces in the family of 2D crystals and complex oxides.

In the family of 2D crystal transition metal dichalcogenides (TMDs) alloys, we show the formation of chemically ordered states and vacancy/dopant coupling that leads to unusual relaxation effects around dopant-vacancy complexes. In addition, we explore stability and transition dynamics of defects leading to grain boundary migration in monolayer TMDs under electron beam irradiation. In the family of complex oxides, structural distortions at domain walls and interfaces can directly tune their resulting macroscale physical and electronic properties leading to multiferroics, photovoltaic behavior, and two dimensional electron gas. Using high resolution STEM imaging, this presentation will also focus on our recent efforts on the metrology of the polar displacements in a variety of complex oxide nanostructures such as LiNbO3, brownmillerite superlattices, as well as polar metals.

Bio

Nasim Alem is an assistant professor in the Materials Science and Engineering department at the Penn State University. Nasim received her B.S. degree in Metallurgical Engineering from Sharif University of Technology, Tehran, Iran and her M.S. degree in Materials Science and Engineering from Worcester Polytechnic Institute. She received her PhD from the Materials Science Department at Northwestern University. Nasim has been a postdoctoral researcher in the Physics Department at University of California Berkeley and National Center for Electron Microscopy (NCEM) at Lawrence Berkeley National Lab, before joining Penn State in 2013. Her awards include NSF CAREER award, Wilson research grant, and NCEM young investigator fellowship. Alem group research is focused on probing the atomic and chemical structure of the defects, edges, grain boundaries and interfaces and their stability and transition dynamics using scanning/transmission electron microscopy imaging and spectroscopy.