Initial stages of CuAu(111) oxidation; Oxygen induced Cu segregation and the protective Au layer profile

Tsuda, Yasutaka*; Oka, Kohei*; Makino, Takamasa*; Okada, Michio*; Dio, W. A.*; Hashinokuchi, Michihiro*; Yoshigoe, Akitaka ; Teraoka, Yuden; Kasai, Hideaki*

We report results of our experimental and theoretical studies on the Au concentration profile of CuAu(111) during oxidation by hyperthermal O molecule beam at room temperature, using X-ray photoemission spectroscopy, in conjunction with synchrotron radiation, and density functional theory. Before O 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 bulk.