Abstract
We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces. This forms a protective layer that hinders further oxidation into the bulk. The higher the concentration of Au in the protective layer formed, the higher the protective efficacy. As a result, of the three Cu-Au surfaces studied, Au3Cu(111) is the most stable against dissociative adsorption of O2, even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K.
Highlights
To characterize the corresponding surfaces, we use X-ray photoemission spectroscopy (XPS) measurements in conjunction with synchrotron radiation (SR)
The atomic density of Cu (Au)-4f XPS spectra were fitted with the Voigt function, defined as the convolution of a Lorentzian with a Gaussian line shape
Similar to Cu3Au(100)[10,11,35], Cu3Au(110)[12], and Cu3Au(111)[13], we can clearly separate both the Au-4f7/2 and Au-4f5/2 XPS peaks into bulk (B) and surface (S) components
Summary
Alloy Surfaces: Effect of Bulk Au received: 05 March 2016 accepted: 13 July 2016. Michio Okada[1], Yasutaka Tsuda[1], Kohei Oka[2], Kazuki Kojima[2], Wilson Agerico Diño[2,3], Akitaka Yoshigoe4 & Hideaki Kasai[5]. We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces This forms a protective layer that hinders further oxidation into the bulk. Even after prolonged doses of 2.3 eV hyperthermal O2 molecular beam (HOMB), there were no obvious Cu2O growth observed on (100) and (111) These results suggest that alloying of Cu-based materials with Au works as an efficient protection against oxidation into the bulk[10,11,23]. Theoretical studies support the same conclusion with regard to the protective nature of the surface Even on such initially inert surfaces, protection against oxidation fails for processes occurring at higher temperatures. We carried out similar calculations for bulk Cu, bulk Au, bulk CuAu, bulk Au3Cu, and O2
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