Core level photoionization spectroscopy of supported metal clusters: Cu55 on silica

Inner-shell photoabsorption, photoelectron and Auger spectra of mass-selected Cu-55 clusters are presented which have been deposited onto the natural silica surface layer of a doped Si-wafer. The core level spectra of the Cu-55-cluster reveal distinct differences with respect to the bulk. Moreover, a non-fcc like structure of deposited Cu-55 clusters can be concluded from the L-3 photoabsorption spectrum. Upon airation of the deposited clusters an oxidation becomes very prominent in the absorption spectra. Both the formation of Cu2+ and Cu1+ ions are evident. Under continuous X-ray irradiation the Cu2+ ions are photoreduced to Cu1+ as seen by the changes in the photoabsorption spectrum as function of time. The 2p(3/2) XPS line of the Cu2+ ions of oxidised Cu-55 shows a positive binding energy shift while almost no shift is observed for the Cu1+ ions. The Auger spectrum of oxidised Cu-55 is shifted to smaller kinetic energy compared to pristine Cu-55 and bulk. (C) 2010 Elsevier B.V. All rights reserved.