Deposition of metallic clusters on a metallic surface at zero initial kinetic energy: evidence for implantation and site exchanges

We have investigated the deposition at zero impact kinetic energy of the Ag atom and clusters (Ag/sub 7/,Ag/sub 19/) on the (100) and (111) surfaces of Pd by molecular dynamics simulations performed within the embedded atom-method scheme. Our results elucidate the role played by the adsorption energy in determining the final morphology of the cluster/substrate system when ideal nondestructive deposition conditions are implemented. While implantation of the atom is not observed, we find a finite probability of site Ag-Pd exchanges in the case of clusters. Deposition-assisted mixing occurring at the topmost surface layer appears to be correlated to the size of the cluster and the orientation of the substrate, being higher for Ag/sub 7//Pd(100) and lower for Ag/sub 19//Pd(111). Total-energy calculations, combined with an analysis of the atomic motion, indicate that the structural transformation accompanying the deposition of the cluster provides the needed activation energy to induce the observed Ag-Pd atomic exchanges.