Copper Oxidation on Pt(111)—More than a Surface Oxide?

Abstract

The growth of copper oxide thin films on a Pt(111) support has been analyzed with a combination of scanning tunneling microscopy, electron-diffraction, and X-ray photoelectron spectroscopy. At low preparation temperature, only a monolayer oxide is formed, whereas most of the precipitated copper accumulates as Cu(111) at the Pt interface. The respective films thus resemble the well-known “29” and “44” surface oxides that are composed of distorted Cu–O six-membered rings and develop in a similar manner upon low-pressure oxidation of Cu(111). With increasing temperature, unreacted Cu mixes with the Pt top layers, resulting in a well-ordered Cu3Pt surface alloy. Following these structural and chemical modifications in the support, the surface oxide undergoes an order–disorder transition, in which the Cu–O honeycomb layer forms an increasing number of 5–7 defects and later disrupts into isolated oxide islands. The most prominent island types, especially at high temperature, are Cu3O shamrock units bound to Pt surface atoms that self-assemble into highly crystalline 2√3 domains on the surface. The preparation of thicker Cu2O films, on the other hand, appears challenging on Pt(111), partly because of difficulties to oxidize copper in a vacuum experiment and partly because of an unfavorable lattice match.