IN-SITU X-RAY SURFACE DIFFRACTION OF COPPER UNDERPOTENTIAL DEPOSITIONON AU(100)

In order to investigate the copper underpotential deposition (upd) on gold single crystals, X-ray surface diffraction (XRSD) measurements we re performed under in-situ conditions. After formation of a complete C u upd layer, Cu was found to adsorb in a commensurate p(1 x 1) structu re in fourfold hollow sites with a vertical distance of 1.4 Angstrom f rom the Au(100) surface. The coverage obtained by XRSD was (65 + 8)%. The structure of the Cu upd layer was studied as a function of applied potential and of the Cu-ion concentration in solution. The Cu-ion con centration did not affect the structure of the Cu upd layer. As a func tion of the applied potential, it was possible to investigate the form ation of the Cu upd layer by XRSD. From a comparison between the XRSD results and the cyclic voltammetry, the formation of an ionic adlayer is inferred for the Cu upd on Au(100) in perchloric acid. (C) 1997 Els evier Science S.A.