Underpotential deposition behavior of metals onto gold electrodes coated with self-assembled monolayers of alkanethiols

Underpotential deposition (upd) of Tl, Pb, Ag, Cd, Cu, and Bi on an Au (111) / mica electrode coated with a self-assembled monolayer (SAM) of alkanethiols has been investigated by voltammetry and STM observations. It was found that upd of metals took place on the SAM-coated Au electrode if the alkylchain length of the thiol was shorter than C8. The cathodic waves showing deposition of metal atoms were negatively shifted or suppressed by coating the electrode with the SAM because of blocking effects of the SAM. Apparently, the blocking effects of the SAM were influenced by the Stokes radius of the metal ions and became marked with increasing Stokes radius. STM observations of the octanethiol-covered Au(111)electrodes revealed that the deposited Ag gave islands of atomic monolayers on which octanethiol molecules were adsorbed hexagonally as the case of the Au. It was found that Ag upd took place both on etch pits and on top of the Au surface, the former being more predominant in an early stage of the Ag upd. (C) 1999 Elsevier Science S.A. All rights reserved.