Skip to content. Skip to main navigation.

Probing Surfaces and 2-D Materials with Beams of Low Energy Positrons

Friday, February 10, 2017, 11:00 AM - 12:30 PM
Nedderman Hall, Room 203

Add to Calendar

Alexander H. Weiss, Ph.D.
Professor and Chair
Department of Physics
University of Texas at Arlington

Abstract

The annihilation of positrons with core electrons results in unique signatures in the spectra of Auger-electron and annihilation-gamma rays that can be used to make clear chemical identification of atoms in the environment of the positron at the time of annihilation. Positrons implanted at low energies trap with high efficiency at an image-correlation just outside the top layer of atoms at the surface. This makes it is possible to use annihilation induced Auger and Gamma signals to probe the surfaces of solids with single atomic layer depth resolution. In this talk we will report recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) and Auger-Gamma Coincidence Spectroscopy (AGCS) to the study of surface structure and surface chemistry. Our research has demonstrated that PAES can be used to obtain Auger spectra with the extremely low background, and increased surface sensitivity and can thus provide new information regarding the composition of the top-most atomic layer. The applicability of PAES to catalytically important surfaces of oxides and the surfaces of 2-D systems including the Topological Insulator, Bi2Te2Se, and Graphene will be discussed in the light of recent measurements. We will conclude with a discussion of the use of Auger-Gamma and Gamma-Gamma coincidence spectroscopy for in-situ studies of surfaces.
Research Supported by NSF-MRI 1338130 and NSF-DMR-1508719

Bio

Prof. Weiss is currently Professor and Chair of the Physics Department at the University of Texas at Arlington. He received his Ph.D. degree from Brandeis University in 1983 where his Ph.D. research resulted in the first measurement of Low Energy Positron Diffraction (the first ever measurement of diffraction of anti-matter from matter) and first measurements of the energy and angular distributions of low energy electrons from surfaces emitted as a result of positron bombardment. After receiving his Ph.D., Dr. Weiss was a post-doctoral researcher at Harvard University where he performed the first x-ray scattering measurements from liquid-gas Interfaces. Since joining the University of Texas at Arlington in 1984 his research has been focused on the development of advanced methods for the characterization of surfaces and thin films and the application low energy positrons in the study of the growth and stability of thin films and nano-structures. Prof. Weiss is the inventor of Positron annihilation induced Auger Electron Spectroscopy (PAES). Research in his laboratory at UTA provided the first demonstration that PAES selectively probes the elemental content of the top-most atomic layer of surfaces and that background free Auger spectra can be obtained by utilizing incident positron beam energies below the secondary electron emission threshold. Current research in Prof. Weiss’ lab is making use of these properties in employing very low energy (<1 eV) positron beams to study Auger decay of annihilation induced valence band holes in layered materials including single layer graphene.

Return to Upcoming Events

 ∧