CU FILMS ON A ZN-TERMINATED ZNO(0001) SURFACE - STRUCTURE AND ELECTRONIC-PROPERTIES

The structure and electronic properties of ultrathin, vapor-deposited Cu films on a Zn-terminated ZnO(0001)-Zn surface have been studied wit h low-energy ion scattering spectroscopy (ISS), X-ray photoelectron sp ectroscopy (XPS) and X-ray photoelectron diffraction (XPD), low-energy electron diffraction (LEED), work function and band bending measureme nts. Below similar to 5% of a monolayer (ML). the Cu is very weakly ca tionic, but thereafter, it is practically charge-neutral and clustered into islands with strong Cu-Cu bonding. Up to similar to 33% of a ML, these islands are only one atom thick, and the Cu atoms do not sit in preferred substrate lattice sites. Above similar to 33% of a ML, addi tional Cu adds predominantly on top of existing Cu islands, to make th ree-dimensional (3D) Cu islands. These eventually adopt a Cu(111) stru cture, rotationally aligned with the ZnO(0001) substrate, when the ind ividual islands are 3 ML thick or thicker. Annealing above 500 K cause s the islands to irreversibly thicken, thus uncovering part of the ZnO surface. The results are compared to Cu films on other faces of ZnO, showing that the geometry of the ZnO surface has only minor effects on the Cu film properties, although the conversion from 2D to 3D islands happens at a lower coverage on this Zn face than on the O face. (C) 1 998 Elsevier Science B.V. All rights reserved.