Chemical effects in the Auger spectrum of copper-oxygen compounds

AES and XPS are two powerful techniques for the determination of the compos ition of a surface. The nature of the chemical binding of an element is usu ally studied by XPS. However, the Auger peaks also contain theoretical info rmation about the chemical environment of the elements. As mostly one or tw o valence levels are involved in the emission of the Auger electron, a care ful analysis of the Auger lines should allow to reveal the changes in the e lectron densities in the electronic levels due to a change in the chemical environment. However, for metals (with a high number of electrons) the chem ical 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, C u2O, CuCO3 and copper acetate standard samples were prepared and characteri sed. The copper LMM lines were analysed. The energy shifts, change in relat ive intensities and change in FWHM were studied as a function of increasing oxygen environment. We show that the energy shift and the relative intensi ties of the Auger peak are good fingerprints of the oxidation state, and th at the width of the Cu L3M4.5M4.5 peak can be related to the width of the v alence band. (C) 1999 Elsevier Science B.V. All rights reserved.