Electrochemical and Scanning Tunneling Microscopic Study of Dealloying of Cu3Au

Abstract

Dealloying of has been examined by in situ STM and several electrochemical methods. Three different regimes of behavior were noted. At low overpotentials, clustering of gold atoms occurs near sites of copper dissolution. This is essentially a two‐dimensional process. The formation and smoothing of these clusters by capillary action, monitored in real time, demonstrated the highly mobile nature of the surface species. At higher potentials, the electrode is largely passivated by the enrichment of gold. However, there exist small localized regions of three‐dimensional roughness which may be correlated to extended dealloying catalyzed by bulk solid‐state defects. When the potential is increased above the critical potential , global surface roughening occurs. Correlating STM with chronoamperometric and chronopotentiometric results demonstrates that this transition occurs by nucleation and growth. Selective dissolution of copper depends on the exposure of fresh sites by the migration of passivating gold atoms. Adsorption can strongly influence this transport process, as manifest by changes in . In comparison to sulfate media, chloride caused a decrease in , while derivatization of with an alkyl‐thiol produced an increase in . These shifts are consistent with the enhancement and inhibition of gold surface diffusion by the respective adsorbates.