In Situ STM Observation of Roughening, Annealing and Dissolution of Gold (111) in an Electrochemical Cell

We report in situ scanning tunneling microscopy (STM) at atomic layer resolution of the topographic changes accompanying electrochemical reactions at an electrode surface. In dilute perchloric acid, gold (111) terraces roughen during the electrochemical formation and reduction of more than a monolayer of gold oxide. The surface anneals in minutes at a moderate electrochemical potential and room temperature. Small amounts of chloride in the electrolyte solution enhance monatomic step motion, prevent the observation of roughening following oxidation and rereduction, and promote the dissolution of gold from step edges during oxidation and rereduction. These observations illustrate the role adsorbates have in determining the surface mobility and solubility of substrate atoms. More generally, they illustrate the power of the STM to probe the electrochemical interface.