EVOLUTION OF THE ELECTRONIC AND GEOMETRIC STRUCTURES OF SIZE-SELECTEDPT AND PD CLUSTERS DEPOSITED ON AG(110) OBSERVED BY PHOTOEMISSION

Mass-selected Pt-n and Pd-n (n = 1-15) clusters, generated by ion bomb ardment, are deposited at room temperature in submonolayer quantities on Ag(110) single-crystal surface and characterized by electron spectr oscopy (XPS, UPS). Different sites, reflected in the Pt-5d and Pd-4d b inding energies, are observed as a function of the substrate temperatu re, indicating clearly the surface-subsurface atom exchange processes. The monodispersed clusters indicate individual discrete electronic st ructure features of the Pt-5d and Pd-4d emission. For the monomers vir tual bound-state formation as in dilute (3%) PtAg and PdAg alloys is o bserved. With increasing cluster size, firstly, the increasing splitti ng between the bonding-like and antibonding-like d-states reflects the increase in cohesive energy due to molecular interaction, and secondl y, the shift of the center of gravity of the d-emission towards the Fe rmi energy indicates the trend to transition-metal formation.