An investigation of transition metal clusters deposited on graphite and metal oxide substrates by a combined use of XPS, UPS and Auger spectroscopy

Cu and Ni clusters deposited on graphite and metal oxide (TiO2, Al2O3) supports have been investigated by X-ray and UV photoelectron spectroscopy as well as Auger electron spectroscopy. The 2p core-level binding energy of the cluster increases with the decrease in the cluster size and the maximum shift in the case of the smallest cluster is 0.8–1.4 eV (relative to the bulk), the actual value depending on the substrate. The metal LMM Auger line shifts to lower kinetic energies with the decrease in the cluster size and this shift is considerably larger (1.4–3.3 eV) than that of the 2p binding energy. The shifts in the position and intensities of the valence bands with the cluster size have also been studied; the 3d band intensity approaches zero for the smallest cluster size studied by us, the number of atoms in the smallest cluster being in the range 25–75. One of the conclusions from the study is that the magnitude of the shifts in the core-level binding energy and the Auger kinetic energy due to the decrease in the cluster size depends on the substrate, being largest on an insulating substrate such as Al2O3 and least on graphite.