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Vol. 29 (2008) No. 7 P 407-412




Angle-resolved photoemission measurements are carried out to investigate the valence electronic structures of two different ZnO surfaces that are (0001) Zn-terminated (ZnO-Zn) and (000-1) O-terminated (ZnO-O) surfaces, and also of Cu clusters supported on these surfaces. On the clean ZnO surfaces, two valence bands are observed at ∼4 and 5−8 eV with a clear dispersion feature. Although these bands are associated with the bulk bands, it is found that the dispersion widths of the bands exhibit the termination dependence of the polar ZnO surfaces. Deposition of Cu on the polar ZnO surfaces induces downward bending of the ZnO band. Magnitude of Cu-induced bending is larger on ZnO-O than on ZnO-Zn. This indicates that the Cu—ZnO interface interaction is greater for the Cu/ZnO-O system than for the Cu/ZnO-Zn system. The analysis of the Cu 3d band structure implies that coupling between the Cu 3d band and the ZnO band is operative at the Cu—ZnO-O interface, whereas such coupling seems to be missing at the Cu—ZnO-Zn interface. We propose that the effect of electronic coupling is one of the factors that determine the interface interaction between the Cu cluster and polar ZnO surfaces.