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.