Initial- and final-state effects on metal cluster/substrate interactions, as determined by XPS: copper clusters on Dow Cyclotene and highly oriented pyrolytic graphite

We have been studying X-ray-excited Auger parameter [α′=EB (Cu2p3/2)+Ek (L3M4,5M4,5)] and Wagner (Ek versus EB) plots of Cu clusters deposited onto Dow Cyclotene and highly oriented pyrolytic graphite (HOPG) by evaporation and sputtering. The cluster size has been found to be determined by cluster/substrate interfacial interactions, which depend on the method of deposition and the substrate surface treatment. The Auger parameter has been found to depend only on the cluster size under any given deposition condition, and its magnitude has been found to be proportional to the reciprocal of the average cluster radius, irrespective of surface treatment; this indicates that Δα′ is dominated by microscopic cluster effects. Wagner plots have invariably been found to show linear relationships. We discuss these observations in terms of the influences of initial- and final-state effects.