Oxidation of a Zn-deposited Cu(1 1 1) surface studied by XPS and STM

The oxidation of a Zn-deposited Cu(1 1 1) surface was studied by XPS and STM. When oxidizing the Zn/Cu(1 1 1) surface at high temperatures as 600–673 K, hexagonal ZnO islands rotated by 30° with a unit vector of 4.8 Å were formed over the Cu(1 1 1) surface. As precursor species for the formation of the ZnO species on Cu(1 1 1), alternating islands of a Cu–Zn surface alloy and Cu2O were imaged as a striped structure by STM, in which these two islands coexisted on a single terrace. The terraces were regularly separated by step edges. The oxidation of the Cu–Zn surface alloy into the ZnO species was consistent with the previous results of Cu/ZnO-based powder catalysts, in which the ZnO/Cu interface was regarded as the active site for methanol synthesis by hydrogenation of CO.