Electronic excitations on silver surfaces

Abstract

The surface electronic structure and optical response of Ag has been studied using angle- and energy-resolved photoyield (AERPY) and angle-resolved photoemission spectroscopy (ARPES) using low energy photons (2.7-18 eV). ARPES data for Ag(100) exhibit an unexpected dispersing feature which cannot be assigned to a direct transition peak in the ΓX direction of the bulk Brillouin zone. The origin of this feature is found in the surface mediated indirect transitions related to the direct transition in the ΓL direction. From the AERPY experiments, the adlayer standing-wave-like bulk plasmon mode is clearly observed in Ag(100) and Ag(111) thin films. The silver multipole plasmon is observed both on Ag adlayers and bulk single crystal surfaces at 3.7 eV. No signature of the multipole plasmon is observed around 6.7 eV, in disagreement with the prediction of the s-d polarization model.