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

Abstract

Size-selected Cu n + 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 >10 14 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 × 10 12 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 L 3-edge is located above the corresponding 2p 3/2 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 (2p 3/2).