Experimental and Theoretical Studies on Oxidation of Cu-Au Alloy Surfaces: Effect of Bulk Au Concentration

We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu(3)Au(111), CuAu(111), and Au(3)Cu(111), using hyperthermal O(2) 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, Au(3)Cu(111) is the most stable against dissociative adsorption of O(2), even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K.