EFFECT OF ANION ADSORPTION ON EARLY STAGES OF COPPER ELECTROCRYSTALLIZATION AT AU(111) SURFACE

The monolayer and submonolayer deposition of copper on Au(111) electro de surface in the presence of chloride and sulfate ions was studied by in situ X-ray absorption and electrochemical techniques, The anions c oadsorb with the deposited copper adatoms and have a strong influence on the structure of these mixed overlayers. Copper deposited in the pr esence of chloride forms a bilayer in which copper atoms are sandwiche d between the gold substrate and the top layer of chloride ions. The b ilayer is well ordered and has a (5 x 5) long range structure, The cop per atoms are packed in registry with the top layer of chloride ions. In contrast, copper adatoms deposited in the presence of sulfate ions are packed in registry with respect to the Au(lll) substrate. The coad sorbed copper and sulfate form a highly corrugated overlayer. The copp er adatoms assume a honeycomb (root 3 x root 3) structure with the cen ter of the honeycomb occupied by sulfate. The sulfate ion adsorbs with three of its four oxygens directed towards the hexagon of copper adat oms. The bond angle between the copper adatom and the oxygen of the su lfate ion is approximately equal to 45 degrees. Our data indicate that , in contrary to the literature reports, the (root 3 x root 3) structu re observed on STM and AFM images corresponds to the corrugation of ad sorbed sulfate ions rather than copper adatoms.