Low-energy alkali ion scattering as a probe of resonant charge exchange on cesiated Cu(110)

Abstract

Intensities of K+ and Li+ scattered from cesium-covered Cu(110) surfaces are measured as a function of cesium-induced work function shifts ΔΦ, for ΔΦ up to ∼2 eV from the clean surface value. Various scattering geometries are used with beam energies ranging from 100 eV to 1 keV. Scattered K+ energy spectra indicate that the adsorbate-induced changes in intensity are uniform for all scattered K+ energies. Energy-integrated scattered K+ intensities are measured as a function of the work function Φ, for different beam energies and scattering geometries. The intensity decrease with decreasing Φ is attributed to an increase in the resonant electron transfer rate from the surface to the scattered particles. The work function dependence and the velocity dependence of the intensity decrease cannot be reproduced with a model of resonant charge transfer that treats the effect of the adsorbate layer as a uniform shift in the work function. To explain the observed charge transfer rates, both local and collective effects from the presence of low-coverage cesium adsorbates must be considered.