An Experimental Proof of the Back-Scattering Model for Dichroic Effects in Vuv Photoemission

Abstract

The energy dependence of the circular dichroism in the angular distribution of photoelectrons (CDAD) was investigated from the shallow Cs 5p core levels. Cesium was prepared in a hexagonal ordered monolayer on W(110). The results are mainly influenced by scattering of the photoelectrons within the adlayer. At low energies, the behavior observed is described by means of a model that treats only the back-scattering of photoelectrons at the potential step between the adlayer and the substrate. It leads to a simple method determining the position of the monolayer with respect to the substrate. In this approach, the back-scattering model is matched with the measured energy dependence of the CDAD between hν = 21 eV and hν = 33 eV. This procedure yields reliable results already for a single observation angle of the photoelectron. The distance between cesium and tungsten was determined to be (2.2 ± 0.1)Å, which corresponds to the effective distance between the center of the adsorbed layer and the potential step between the layer and the substrate. Finally, the fitted result was proven to meet the complete angular dependence of the CDAD at different photon energies.