UPS AND XPS STUDIES OF CU CLUSTERS ON GRAPHITE

The electronic structure of small copper clusters deposited on polycrystalline graphite has been studied by means of UPS and XPS spectroscopies as a function of the cluster size. The Cu d-band, Fermi edge and 2p core levels have been carefully analyzed. As the cluster dimension decreases, the Fermi edge shift is very small, less than 0.1 eV for the smallest clusters, while the d-band and the 2p core level peaks move towards higher binding energy of 1 and 0.4 eV, respectively. These results show a strong variation of the electronic structure of Cu clusters when their dimension decreases. The effect of the decreased screening of the valence band electrons and of the charge left on the cluster after the photoemission process seem to be negligible.