Inner-shell photoelectron spectroscopy of size-selected Cu-clusters on Si

Size-selected Cun+ clusters have been deposited onto a p-doped Si-wafer and have been spectroscopically studied by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). At a cluster coverage of >1014 cm−2 the XANES and XPS spectra appear very similar to the bulk while X-ray spectra of individual, non-agglomerated clusters are observed at a cluster coverage of <8 × 1012 cm−2. In the latter spectra, both the L-absorption edge as well as the 2p core ionization potential are higher in energy than the respective bulk value. For all measured clusters the L3-edge is located above the corresponding 2p3/2 ionization energy similar to the bulk. Additionally, the absorption energy of the L-edge decreases with increasing cluster size. Upon oxidation of the cluster a strong excitonic absorption feature appears below the core ionization potential (2p3/2).