INFLUENCE OF SURFACE DEFECT STRUCTURE ON THE UNDERPOTENTIAL DEPOSITION OF PB MONOLAYERS AT AG(111)

The underpotential deposition (upd) of Pb monolayers at Ag(111) thin-f ilm electrodes in perchlorate solutions have been investigated as a fu nction of the substrate defect structure. Ag(111) films were grown epi taxially on muscovite mica by thermal evaporation and annealed at 300 degrees C at 10(-6) Torr for periods between 0 and 12 h. X-ray diffrac tion and electrochemical scanning tunneling microscopy indicate that t hermal annealing significantly increases the degree of film crystallin ity and smoothness. A more ideal voltammetric response for the upd of Pb was obtained using Ag thin-film electrodes that were annealed for p eriods longer than 6 h. Specifically, the width of the upd voltammetri c wave, as well as the splitting between the cathodic and anodic peaks , was found to decrease with an increase in annealing time. Surface ro ughness factors (defined as the ratio of the electrochemically-active area relative to the geometric area) for the Ag(111) films decreased f rom 1.15 for unannealed films to 0.99 +/- 0.03 for films after 12 h of annealing. The results indicate that previously reported voltammetric features observed for the upd of Pb monolayers in perchlorate solutio ns are associated with Pb deposition at Ag(111) surface defect sites.