An insitu surface differential diffraction and anomalous scattering investigation of surface relaxation during underpotential deposition of Ag on Au(111)

Abstract

An insitu X-ray diffraction investigation, using surface differential diffraction (SDD) and anomalous scattering, has been carried out to study relaxation of the substrate surface occurring during the underpotential deposition of silver onto the Au(111) surface. Although the SDD profile is affected by all structural changes at the surface, only a single structural parameter may be extracted from a single differential profile. However if data are collected at a number of different wavelengths then the variation of scattering factors may be used to distinguish relaxation of the substrate from adsorption. Data were collected at three different wavelengths λ₁=1.499 Å (30 eV below the Ni edge), λ₂=1.073 Å (200 eV below the Au edge), and λ₃=1.045 Å (30 eV below the Au edge). Combined analysis of this data shows that during underpotential adsorption of silver the surface gold layer undergoes a compressive relaxation of 0.10 Å, which is in agreement with values reported in the literature. This shift was found to be independent of potential variation.