Early Stages of Copper Electrocrystallization: Electrochemical and in Situ X-ray Absorption Fine Structure Studies of Coadsorption of Copper and Chloride at the Au(111) Electrode Surface

Cu K-edge X-ray absorption spectra (XAS) recorded in situ using glancing incidence and fluorescence detection have been employed to study the codeposition of copper and chloride ions on a Au(111) surface under an electrolyte solution. Chronocoulometric measurements provided information about the composition of the overlayer and about the number of electrons flowing to the interface per adsorbed copper ion. The XAS displays a remarkable dichroism consistent with a bilayer in which the Cu adatoms are covered by chloride ions. Previous scanning tunneling microscopy (STM) measurements suggested either a (5 × 5) long-range structure similar to that of the (111) plane of a CuCl crystal or to (4 × 4)-based structures. FEFF 6.01 multiple scattering calculations of the XAS were performed on five different model structures derived from the STM proposals. A unique solution could not be obtained. The results indicate that there is a large degree of static disorder. They rule out high-symmetry structures in which there are narrow distributions of Cu−Cl, Cu−Au, and Cu−Cu distances and bond angles.