The three-step model in electron spectroscopy revisited I. Angular distribution of Auger electron emission from non-crystalline Al, Si and Cu surfaces

Measurements are presented of the Auger electron intensity emitted from non-crystalline Al, Si and Cu samples as a function of the emission angle, for a constant angle of incidence of the primary electrons. For this particular geometry, all features in the experimental angular distribution are completely attributable to the processes playing a role in the electron escape. It is found that surface roughness and electron refraction at the potential barrier do not affect the shape of the angular distribution. The angular distribution of the high energy core lines (CCC) are perfectly described by a cosine distribution. A distinct deviation of this behaviour is observed for the low energy valence band (CVV) transitions that is caused by the influence of surface excitations. Analysis of reflection electron energy loss spectra (REELS) demonstrates that for energies≳1000 eV, the increase of surface excitations when going to more oblique emission angles is compensated by a decrease in the probability for bulk excitations. This complementarity of surface and bulk excitations is not perfect at lower energies and leads to a significant net effect of surface excitations. In particular, it is empirically found that the CVV angular distribution is consistent with the simple model in which it is assumed that bulk inelastic collisions occur homogeneously throughout the semi-infinite solid.