Electronic structure of Cu on ZnO(10(1)over-bar-0): Angle-resolved photoemission spectroscopy study

Angle-resolved photoemission measurements are carried out to investigate the valence electronic structure of Cu on ZnO(10 $$(1) over bar0). The coverage-dependent measurements of the Cu 3d and 4sp bands reveal that the growth of the Cu overlayer is characterized by a cluster formation. These Cu clusters are semiconductors with an energy gap around the Fermi level at the initial stages of adsorption, while the metallic nature is developed with increasing coverage. The Cu 3d state forms a band with a bulklike energy dispersion at high Cu coverages, whereas the two-dimensional (2D) band is formed in the low-coverage region, where the clusters are semiconducting in nature. From the dispersion relation of the 2D Cu 3d band, the arrangement of the Cu adatoms within the clusters is found to be strongly influenced by the surface structure of ZnO(10 $$(1) over bar0), i.e., the Cu adatoms are linearly arranged along the Zn-O dimer rows of the substrate surface.