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Paper AS-FrM8
Experimental and Theoretical Study of the Chemical Effects in the Auger Spectra of Aluminium, Copper and Carbon Compounds

Friday, November 2, 2001, 10:40 am, Room 134

Session: Catalysis and Surface Reactivity
Presenter: F. Reniers, Universite Libre de Bruxelles, Belgium
Authors: B. Timmermans, Universite Libre de Bruxelles, Belgium
N. Vaeck, Universite Libre de Bruxelles, Belgium
F. Reniers, Universite Libre de Bruxelles, Belgium
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The bonding and electronic structure information of surface atoms is most often studied by XPS, where the energy shift of a photoelectron peak can be ascribed to a change in the chemical environment. Because three atomic levels are involved in the Auger emission process, the use of Auger spectroscopy to obtain this information from peaks positions and line shape is more difficult. However, new progresses in signal analysis techniques make the extraction of most chemical information intrinsically present in the Auger spectra possible. The advantage of AES over XPS is its higher lateral resolution allowing the study of the surface distribution of the elements (Auger mapping), which, combined with modern computational methods, opens new opportunities in surface analysis. In order to try to correlate the changes in the Auger peaks with the changes in the chemical environment, we performed a full experimental and theoretical study of the Auger lines of aluminium, carbon and copper in several compounds. The changes in the peak energies and shapes were recorded in model spectra. Deconvolution of the peaks was achieved by factor analysis. The experimental results are compared to ab initio calculations based on a new cluster model including chemical, structural and relaxation effects. Al and C compounds, specifically, present important line shape modifications of valence Auger peaks that can be compared with calculations based on the knowledge of valence densities of states. These were obtained experimentally from XPS and theoretically from a full potential linearized augmented plane wave method within DFT. Further improvements came from accounting the final state hole-hole interaction by the well-known Cini-Sawatzky model.