INFLUENCE OF THE SUBSTRATE OXIDATION-STATE IN THE GROWTH OF COPPER CLUSTERS ON AL2O3(0001) SURFACE - A XANES AND EXAFS STUDY

Surface sensitive X-ray absorption spectroscopy has been used for inve stigating the differences in the environment of copper atoms at the Cu /Al2O3 interface for different oxidation states of the alpha-alumina s ubstrate. We have prepared in situ both oxidised and reduced cu-alumin a surfaces and have evaporated equal amounts of copper (similar to 80% monolayer) on each. Under our experimental conditions, we infer that: (a) the interface grows via the Volmer-Weber mode rather than the Str anski-Krastanov mode suggested in the literature. (b) The morphology o f supported Cu clusters depends strongly on the oxidation state of the alumina. For equal amounts of copper, much larger clusters are found on reduced Al2O3(0001) substrates than on oxidised substrates.