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 It-edge X-ray absorption spectra (XAS) recorded in situ using glanc ing incidence and fluorescence detection. have been employed to study the codeposition of copper and chloride ions on a Au(lll) surface unde r an electrolyte solution, Chronocoulometric measurements provided inf ormation about the composition of the overlayer and about the number o f 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 x 5) long-range st ructure similar to that of the (111) plane of a CuCl crystal or to (4 x 4)-based structures, FEFF 6.01 multiple scattering calculations of t he XAS were performed on five different model structures derived from the STM proposals, A unique solution could not be obtained. The result s indicate that there is a large degree of static disorder, They rule out high-symmetry structures in which there are narrow distributions o f Cu-Cl, Cu-Au, and Cu-Cu distances and bond angles.