Initial stages of Cu3Au(111) oxidation: oxygen induced Cu segregation and the protective Au layer profile

Abstract

We report results of our experimental and theoretical studies on the Au concentration profile of Cu₃Au(111) during oxidation by a hyperthermal O₂ molecular beam at room temperature, using X-ray photoemission spectroscopy (XPS), in conjunction with synchrotron radiation (SR), and density functional theory (DFT). Before O₂ exposure, we observe strong Au segregation to the top layer, i.e., Au surface enrichment of the clean surface. We also observe a gradual Cu surface enrichment, and Au enrichment of the second and third (subsurface) layers, with increasing O coverage. Complete Cu segregation to the surface occurs at 0.5 ML O surface coverage. The Au-rich second and third layers of the oxidized surface demonstrate the protective layer formation against oxidation deeper into the bulk.