Oxidation of copper clusters on : Effect of temperature and preadsorbed water

Oxidation of Cu clusters on the ZnO ( 1 0 1 ¯ 0 ) surfaces has been examined by angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation. Cu deposition on ZnO ( 1 0 1 ¯ 0 ) leads to the formation of the Cu clusters with a metallic electronic structure. Partial oxidation of the cluster is induced by annealing the Cu-covered ZnO ( 1 0 1 ¯ 0 ) surface at temperatures higher than 700 K. Oxidation proceeds via interaction of the Cu adatoms with the O atoms which are migrated from the substrate bulk to the surface due to the thermal activation. The Cu adatoms also aggregate into clusters when they are dosed on the water-preadsorbed ZnO ( 1 0 1 ¯ 0 ) surface at room temperature. These clusters are found to be partially oxidized. The detection-angle dependent measurements of the ARPES spectra of the Cu clusters on the water-preadsorbed surface reveal that oxidized Cu exists on the Cu-cluster surface, i.e. the Cu cluster capped with the oxidized species is induced.