Comparative X-ray photoemission spectroscopy study of Au, Ni, and AuNi clusters produced by laser vaporization of bulk metals

Supported Au and Ni clusters as well as bimetallic AuNi clusters have been produced by laser vaporization of both pure bulk metals and alloy. Transmis sion electron microscopy (TEM) and energy dispersive X-ray spectroscopy (ED S) experiments show that they have a narrow distribution size centered arou nd 2.5 nm and that bimetallic clusters have the same composition as the vap orized Au0.5Ni0.5 alloy. X-ray photoemission spectroscopy (XPS) has been us ed to measure core level binding energy shifts of Au 4f(7/2) and Ni2p(3/2). The shifts observed in the bimetallic system show the combined effects of both alloying and surface local order in relation with strong Au surface se gregation as deduced from previous low energy ion scattering (LEIS) experim ents.