Ion-scattering study and Monte Carlo simulations of surface segregation in Pd-Pt nanoclusters obtained by laser vaporization of bulk alloys

Bimetallic Pd-Pt clusters deposited on amorphous carbon have been produced by laser vaporization of various bulk alloys. Energy dispersive x-ray analysis and transmission electron microscopy show that they have a perfectly well-defined stoichiometry and a narrow range of size. They constitute ideal systems to investigate segregation processes in finite solids. It is shown that low-energy ion scattering allows the determination of surface concentration, which has been found to be different from the overall one. Monte Carlo simulations coupled with a recently developed energetical model, based on a tight-binding scheme that includes bond strength modifications at surfaces, account well for the experimental finding and give information on the surface distribution of the segregating Pd atoms.