Investigation on electronic structure of Cu clusters on graphite by EELS and XPS studies

Abstract

We have applied electron energy loss (EELS) and X-ray photoemission (XPS) spectroscopies to study the electronic structure of copper clusters deposited in situ on clean graphite. The XPS results show an increase in the binding energy of both valence band and core levels when the cluster size decreases. Furthermore the EELS results show a sizeable increase in energy loss for the feature located at about 4 eV involving 3 d → E f states when the cluster size decreases. The observed shifts in the EELS spectrum are the same as those measured for the 3 d valence band shifts in the XPS spectra. Since the electrostatic charging effects, suggested in the past as the explanation for the variation in electronic properties occuring in the XPS of small clusters, cannot be invoked in EELS measurements we interpret the reported shifts as a genuine effect caused by band structure variation due to a redistribution of the states within the cluster d-band.