2D nucleation and growth phenomena in UPD of Cd on Ag(111) and Ag(100)

Abstract

Underpotential deposition (UPD) of Cd on Ag single crystal substrates has been studied by in situ scanning tunneling microscopy (STM) and electrochemical measurements. On Ag(111) the UPD process starts with formation of an expanded adlayer with a Ag(111) - (√3 x √19)R23.4° superlattice structure. In the UPD range 50 mV < ΔE < 80 mV this adlayer transforms by 2D nucleation and growth to a condensed Cd monolayer, which is unstable and at long polarization times undergoes changes involving surface alloy formation phenomena. In contrast to Ag(111), on Ag(100) a formation of a condensed monolayer by 2D nucleation and growth has been observed at relatively high underpotentials (130mV ≤ ΔE ≤ 180mV). The growth rate of 2D clusters extracted from the in situ STM images indicates a surface diffusion-controlled growth kinetics. At lower underpotentials the UPD of Cd on both substrates involves a significant surface alloy formation, which is reflected in the surface topography changes observed during the anodic stripping. ©The Electrochemical Society.