LEED, Auger spectroscopy, and contact potential studies of copper−gold alloy single crystal surfaces

The (100), (111), and (110) surfaces of copper−gold alloy single crystals (Cu, Cu3Au, CuAu, Au3Cu, Au) have been studied. Results are presented for (i) the variation of relative Auger peak strengths with bulk composition, (ii) the variation of work function with orientation and bulk composition, and (iii) the occurrence of surface ordering. The average work function Φ increases as the bulk Au concentration increases from Cu to Au3Cu, with the orientation dependence in accord with the expected variation of surface dipole with ’’atomic roughness,’’ i.e., Φ (111) ≳ Φ (100) ≳ Φ (110); the surfaces of Au do not follow this simple rule. LEED indicates that Au(100), Au(110), Au3Cu(110), and CuAu(110) surfaces have complex structures. Observed differences in the kinetics of ordering of the Cu3Au (100) and (111) surfaces are discussed.