The effects of alloying and segregation for the reactivity and diffusion of oxygen on Cu3Au(111)

Abstract

We report results of the segregation induced by the adsorption of O₂ and the barrier of the formation of Cu₂O in Cu₃Au(111) with an experimental and theoretical approach. Oxidation by a hyperthermal O₂ molecular beam (HOMB) was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident-energy dependence of the measured O-uptake curve, dissociative adsorption of O₂ is less effective on Cu₃Au(111) than on Cu(111). The dissociative adsorption is accompanied by the Cu segregation on Cu₃Au(111) as well as on Cu₃Au(100) and Cu₃Au(110). The obvious growth of Cu₂O for a 2.3 eV HOMB cannot be observed and it suggests that the Au-rich protective layers prevent the diffusion of O atoms into the bulk. The theoretical approach based on density functional theory indicates that O adsorption shows the same behavior on Cu₃Au(111) and on Cu(111). For the diffusion case, the barrier to diffuse into the subsurface in segregated Cu₃Au(111) is higher than in Cu(111). This indicates that the segregated Au-rich layer in Cu₃Au(111) works as a protective layer.