Layer-resolved shifts of photoemission and Auger spectra from physisorbed rare-gas multilayers.

Abstract

Rare-gas multilayers adsorbed on Pd(111), Pd(001), and Al(111) were studied with photoemission and Auger spectroscopy. The Xe 4d core levels and the Xe N/sub 4,5/O/sub 2,3/O/sub 2,3/ Auger transitions show layer-resolved shifts for Xe multilayers on these three substrates. A simple model explains the experimental results satisfactorily. The core-level binding-energy shifts relative to the gas phase are dominated by the final-state hole-screening effect. The Auger kinetic-energy shifts relative to the gas phase, dominated by the difference in initial- and final-state hole-screening energies, are about minus three times the corresponding core-level shifts. The screening energies were calculated using a jellium model for the substrate and a dielectric continuum model for the rare-gas adlayer. Surface-induced shifts of core-level binding energies and Auger kinetic energies for bulk solid Xe(111) were also observed; the theoretical shifts are in very good agreement with the experimental values. The valence levels for multilayers of Ar, Kr, and Xe on Pd(001) were studied. They showed qualitatively similar shifts as the core levels, but the results cannot be explained accurately by our model, because the valence excitations are not as localized as the core excitations. Using spacer layers of Kr and Xe with various thicknesses, the effect of metallicmore » substrate screening on the valence-level shifts of Ar was demonstrated. The issues related to a proper energy-reference level and the question of ionic versus neutral excited states will be discussed.« less