Quantitative model for the surface sensitivity in Auger-photoelectron coincidence spectroscopy (APECS)

The effects of multiple elastic and inelastic scattering on the lineshape in Auger-photoelectron coincidence spectra (APECS) are studied. A simple and at the same time general model is proposed. Model calculations are performed that confirm the well known fact that the surface sensitivity of APECS, when the Auger peak is measured in coincidence with the photoelectron peak, is enhanced as compared to the ordinary ("singles") spectrum. The results also show how the average depth from which the Auger electrons originate can be selected experimentally by recording them in coincidence with the loss features of the photoelectron spectrum and vice versa. Additional simulations reveal why surface and bulk excitations, that can be clearly distinguished in experimental APECS spectra, are uncorrelated to a high degree. This allows one to consistently eliminate the contribution of multiple bulk and surface scattering from experimental APECS data ultimately providing the true energy distribution at the source. (C) 2002 Elsevier Science B.V. All rights reserved.