Inelastic effects and structure in the auger electron emission spectra of V2O5(010) and V(100) surfaces: Study of chemical shifts

Abstract

Characteristic ionization losses and plasma losses occurring in the AES spectra of V 2 O 5 (010) and V(100) surfaces are discussed. The former are used to evaluate chemical shifts of the VL 2 and VL 3 levels in V 2 O 5 . Values of approximateley 2.5 eV are found. These are smaller than the values obtained with ESCA (± 5 eV). It is described how the electron beam used in AES is thought to be responsible for this effect. ESCA data from partly reduced V 2 O 5 samples tend to confirm the proposed model, based on oxygen loss and decomposition of V 2 O 5 single crystals under the influence of the electron beam. The plasma losses of the larger Auger peaks are discussed. It is shown how some fine structure in the spectra can be partly explained by their presence. The plasma losses were simulated with numerical techniques based on the use of a signal averager. Signal averaging, curve fitting and related numerical techniques improve the resolution of AES spectra. Spectra of V 2 O 5 (010) and V(100) obtained in this manner are discussed. With respect to the transitions involving the valence band it is shown that the complex valence band structure is one of the causes of the observed discrepancies between theoretical and experimental AES data. Furthermore there is an uncertainty concerning the way in which ionization correction should be applied in this case. This correction is thought to increase with the degree of localization of the valence electrons. Auger peak intensities in function of the primary energy were found to show a maximum at about 3.5 times the critical potential, as was expected from theory if a moderate amount of backscattering is taken into account. Finally the intensity variations of the Auger peaks under continuous electron bombardment show the rate of oxygen loss at a V 2 O 5 surface due to the primary beam.