Initial stages of Cu3Au(111) oxidation: oxygen induced Cu segregation and the protective Au layer profile

Abstract

We report results of our experimental and theoretical studies on the Au concentration profile of Cu3Au(111) during oxidation by a hyperthermal O2 molecular beam at room temperature, using X-ray photoemission spectroscopy (XPS), in conjunction with synchrotron radiation (SR), and density functional theory (DFT). Before O2 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 the bulk.

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

“…Copper (Cu) and gold (Au) form model binary metallic systems 1 2 3 4 5 6 with stable L 1 0 (CuAu) and L 1 2 (Cu 3 Au and Au 3 Cu) structures. Experimental studies report surface segregation of Au in Cu-Au alloys 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 . More recently, extensive studies 4 10 11 12 13 14 15 16 17 18 19 22 23 on the oxidation of Cu 3 Au surfaces found Au-rich top-most layers of Cu 3 Au(100), (110), and (111) surfaces.…”

“…Experimental studies report surface segregation of Au in Cu-Au alloys 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 . More recently, extensive studies 4 10 11 12 13 14 15 16 17 18 19 22 23 on the oxidation of Cu 3 Au surfaces found Au-rich top-most layers of Cu 3 Au(100), (110), and (111) surfaces. Oxidation, which is one of the more important corrosion process, induces changes in segregation 10 11 12 13 14 15 16 17 18 22 23 24 25 26 .…”

“…More recently, extensive studies 4 10 11 12 13 14 15 16 17 18 19 22 23 on the oxidation of Cu 3 Au surfaces found Au-rich top-most layers of Cu 3 Au(100), (110), and (111) surfaces. Oxidation, which is one of the more important corrosion process, induces changes in segregation 10 11 12 13 14 15 16 17 18 22 23 24 25 26 . Studies have been done to induce Cu segregation to the surface by dissociatively adsorbing energetic O 2 10 11 12 13 22 23 .…”

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

“…Details of the fitting procedure are described in ref. 13. The intensity of the S component decreases with increasing Y and disappears at Y = 0.37 ML.…”

“…In such a context, we reported the profile of (111) segregation. 13 In this study, we found that Au segregation was limited on the top layer without oxidation and that Cu segregation proceeded with increasing adsorbed O coverage. With 0.5 ML coverage of O, the profile of Au concentration is as follows: the Au-poor top layer (0 at%) and the Au-rich second and third layer (47 at% and 45 at%, respectively).…”