Oxidative chloride adsorption and lead upd on Cu(100): Investigations intosurfactant-assisted epitaxial growth

The influence of chloride adsorption and lead upd on the step dynamics of C u(100) has been examined in acid perchlorate solution. A c(2 x 2) Cl adlaye r is formed upon immersion of a Cu(100) electrode leading to step faceting in the [100] direction. At more negative potentials an order-disorder trans formation occurs leading to significant rearrangement of the steps. Alterna tively, in an electrolyte containing Pb2+ th, halide adlayer may be complet ely displaced by lead upd. Images of orthogonal surface steps in combinatio n with an assessment of the coulometry suggest that the lead adlayer forms either a highly defective c(2 x 2), c(5 root 2 x root 2)R45 degrees or a di sordered structure corresponding to a coverage ranging from 0.5 to 0.6. The transformation from the halide to the lead adlayer results in the formatio n of vacancies and adatoms which condense to form holes and islands, respec tively. These features may be rationalized by the formation of an alloy pha se at low coverage, which subsequently dealloys as the coverage approaches 0.5. The extent of the morphological changes associated with the alloying/d ealloying processes is strongly path dependent. Voltammetry reveals that th e stripping of the lead upd layer is associated with two oxidation waves. A s the potential is increased beyond the peak of the first wave islands disa ppear which may be due to alloy formation occurring coincident with partial desorption of the lead. The second wave is associated with the nucleation [100]-oriented rows of the c(2 x 2) Cl adlayer which propagate across the t erraces displacing the lead phase. he use of metal upd and anions as surfac tants in the electrochemical deposition of copper is likely to prove even m ore interesting than in vacuum deposition since the surfactant coverage and its effect on mesoscopic structure can be continuously manipulated by pote ntial control.