Interatomic transitions and relaxation effects in Auger spectra of several gas adsorbates on transition metals

Abstract

A systematic investigation of the fine structure of adsorbate peaks in Auger spectra is presented. Spectra of a wide range of systems involving carbon, sulphur, oxygen, chlorine, and nitrogen adsorbates on copper, nickel, iron, and zinc substrates are reported with a resolution $\frac{\Delta E}{E}\sim 0.006$. According to a previous suggestion two types of transitions are identified and separated in such spectra. Interatomic transitions involve deexcitation of the initial adsorbate core hole from electrons in the substrate valence band. These transitions are rather similar to the ones involved in ion neutralization spectroscopy and are relatively unperturbed by final-state effects. Intra-atomic transitions show the same type of perturbation already observed in other investigations of Auger spectra involving rather localized valence bands, like $d$ bands in transition metals. We identify peaks associated to spectral terms corresponding to final-state configuration interaction. Measurements of the energy of these peaks are used, in connection with photoemission binding energies of other authors, for calculating energy shifts. These shifts are then tentatively analyzed in terms of relaxation energies and, particular, extra-atomic relaxation energies are estimated. A discussion of the general conditions for correlating Auger-electron data and valence-band density of states is offered.