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 prod uced 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. Th ey constitute ideal systems to investigate segregation processes in fi nite solids. It is shown that low-energy ion scattering allows the det ermination of surface concentration, which has been found to be differ ent from the overall one. Monte Carlo simulations coupled with a recen tly 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.