EXCITATION OF SURFACE-PLASMONS ON METALS BY LOW-ENERGY ELECTRONS - THE ROLE OF INTERFERENCE EFFECTS

We present quantitative theoretical studies of the wave-vector dependence of the cross section for excitation of surface plasmons by low-energy electrons incident on the Ag(100) surface. The analysis assumes the dipole mechanism provides the dominant coupling between the electron and the surface plasmon. The theory provides a very good account of the systematic features reported recently by Rocca and Valbusa. As emphasized in earlier theoretical discussions, under conditions used in the experiments, the interference between two excitation channels - "loss then reflection" and "reflection then loss" - enters importantly in the description of the excitation process. In addition, it is essential to include the influence of the image potential on both the amplitude and phase on the scattering amplitude for elastic, specular reflection from the surface.