Chemical effects in the Auger spectrum of copper–oxygen compounds

Abstract

AES and XPS are two powerful techniques for the determination of the composition of a surface. The nature of the chemical binding of an element is usually studied by XPS. However, the Auger peaks also contain theoretical information about the chemical environment of the elements. As mostly one or two valence levels are involved in the emission of the Auger electron, a careful analysis of the Auger lines should allow to reveal the changes in the electron densities in the electronic levels due to a change in the chemical environment. However, for metals (with a high number of electrons) the chemical effects are mostly weak, hidden or hard to interpret. In order to try to understand better the nature of the chemical effects in AES of metals, a systematic study of well-defined copper compounds is performed. Cu, CuO, Cu 2O, CuCO 3 and copper acetate standard samples were prepared and characterised. The copper LMM lines were analysed. The energy shifts, change in relative intensities and change in FWHM were studied as a function of increasing oxygen environment. We show that the energy shift and the relative intensities of the Auger peak are good fingerprints of the oxidation state, and that the width of the Cu L 3M 4,5M 4,5 peak can be related to the width of the valence band.