X-RAY PHOTOELECTRON-SPECTROSCOPY OF SUPPORTED METAL PARTICLES

Small silver and palladium particles supported on carbon, alumina and silica substrates were studied by X-ray photoelectron spectroscopy. With decreasing surface coverage 3d core levels of metal shift toward higher binding energies. Comparable shifts are found for several transition and noble metals deposited on a clean carbon surface, indicating that they have their origin in the final state effects. The magnitude of the shift is considerably influenced by the substrate surface state. On Al//2O//3 and SiO//2 substrates the sign of the metal line-shift is positive for Pd but negative for Ag. This difference is interpreted as a consequence of the different nucleation and growth mechanisms of the two metals. The work is pertinent to catalysis, thin film physics, and photography.