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Probing structure, properties and dynamics of nanostructures through scanning transmission electron microscopy and theory

Speaker: 
Stephen John Pennycook (U. Tennessee, USA)
Date: 
Mon, 13/01/2014 - 2:00pm to 3:00pm
Location: 
T-Lab Level 5 Seminar Rooms
Event Type: 
Other Seminars

Abstract

The aberration-corrected scanning transmission electron microscope (STEM) now allows direct, real space imaging at atomic resolution with low accelerating voltages to minimize damage. In two-dimensional materials such as graphene and transition metal dichalcogenides, atom-by-atom characterization of atomic position, atomic species, chemical bonding and optical and electronic properties has become feasible. Furthermore, through direct momentum transfer, the STEM probe can also reveal the dynamics of small clusters. Movies of a Si6 cluster in a graphene nanopore show conformational changes, which in combination with calculations based on density functional theory, reveals the energy landscape of the cluster. Metallic transition metal chalcogenide nanowires can be sculpted directly from their respective dichalcogenide monolayer sheets. The wires are metallic, with Ohmic contacts to the surrounding two-dimensional layers, and are self-healing against beam damage. In solar cells, the same combination of atomic level microscopy and theory reveals new directions to improve cell effciency.

About the Speaker

Stephen J. Pennycook is a Professor in the Dept. of Materials Science and Engineering, University of Tennessee and the Dept. of Materials Science and Engineering, North Carolina State University. Before his retirement from Oak Ridge National Laboratory in December 2013 he was Corporate Fellow in the Materials Science and Technology Division and leader of the Scanning Transmission Electron Microscopy Group. He received his PhD in physics from the Cavendish Laboratory, University of Cambridge in 1978, joining Oak Ridge National Laboratory in 1982. Pennycook is a Fellow of the American Physical Society, the American Association for the Advancement of Science, the Microscopy Society of America, the Institute of Physics and the Materials Research Society, and is recipient of the Microbeam Analysis Society Heinrich Award, the Materials Research Society Medal, the Institute of Physics Thomas J. Young Medal and Award and the Materials Research Society Innovation in Characterization Award. He has 38 books and book chapters, over 400 publications in refereed journals and has given over 200 invited presentations on the development and application of atomic resolution Z-contrast microscopy and electron energy loss spectroscopy.

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