PHOTOELECTRON-SPECTROSCOPY OF THE AG/PD(110) SYSTEM

Silver interaction with a Pd(110) surface was investigated, in a wide range of Ag coverages, by means of UPS, XPS and TDS. Our XPS measurements of the 3d levels of both Ag and Pd show significant shifts of the Ag signal as a function of Ag coverage, while the Pd level position remains constants. Both, silver and palladium 3d level binding energies were found to be dependent on the thermal treatment of the Ag/Pd system. XPS and UPS measurements strongly suggest that annealing at 500 K induces interdiffusion at the Ag/Pd interface. For the silver multilayers, the interdiffusion of Ag and Pd, due to the annealing at 500 K, is accompanied by structural changes of the silver overlayer (i.e., the formation of silver 3D crystallites). In the valence band spectrum of a silver multilayer annealed at 500 K we have identified a virtual bound state (VBS), derived from the hybridization of the Pd4d level and the silver valence (sp) band, indicating the presence of small concentration of Pd atoms diffused into the silver overlay. With increasing annealing temperature the Pd concentration in the Ag overlay increases causing a broadening of the VBS due to the Pd d-d interaction. At temperatures beyond 800 K desorption of Ag atoms from the palladium surface takes place.