Seminars Archive

Robert Bartynski

Abstract


Friday, September 8, 2000, 14:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
The Electronic Structure of Surface Alloys Determined by Auger-Photoelectron Coincidence Spectroscopy.

Robert A. Bartynski

(Department of Physics and Laboratory for Surface Modification, Rutgers University) ABSTRACT Although many bi-metallic systems are immiscible and do not form bulk alloys, some will mix in the first atomic layer of the host, forming a surface alloy. Random substitutional surface alloys typically occur at very low (< 0.1 ML) impurity concentrations and have potentially interesting chemical and/or magnetic properties. We have used Auger-photoelectron coincidence spectroscopy (APECS) to perform a detailed study of the line shapes of the Ag and Pd M45VV Auger spectra from the Ag/Cu(100), Pd/Cu(100) and Pd/Ag(100) surface alloy systems. The valence levels of these 4d impurity metals have been predicted to exhibit a systematic shift away from the Fermi level as one moves to the right on the Periodic Table, with magnitudes approaching 1 eV for Ag and Pd. As the surface alloy regime only exists for very low impurity concentrations, the highly surface and elemental specific APECS technique is an ideal probe of their properties. We find that the d-bands of Pd shift in the predicted direction but with a much smaller magnitude (of order a few tenths of an eV). The d-levels of Ag appear not to shift at all. Furthermore, correlation effects dominate the line shape of the Pd/Ag(100) system. The implications of these observations, and possible reasons for their discrepancy from the theoretically expected behavior, will be discussed.