O2 induced Cu surface segregation in Au–Cu alloys studied by angle resolved XPS and DFT modelling

Abstract

Surface segregation effects on polycrystalline Au–Cu alloys (Au_0.80Cu_0.20, Au_0.85Cu_0.15 and Au_0.90Cu_0.10) were studied at room temperature by angle resolved XPS (ARXPS) and density functional theory (DFT) before and after exposure to O₂. Au surface enrichment was found as predicted from calculations showing that this process is energetically favourable, with a segregation energy for Au in a Cu matrix of −0.37 eV atom⁻¹. Surface enrichment with Cu was observed after exposure to O₂ due to its dissociative adsorption, in agreement with DFT calculations that predicted an energy gain of −1.80 eV atom⁻¹ for the transfer of Cu atoms to a surface containing adsorbed oxygen atoms, thus leading to an inversion in surface population.