Detailed In Situ Tunneling Microscopy of Single Crystal Planes of Gold (111) in Aqueous Solutions

An in situ electrochemical scanning tunnelling microscope (ESTM) was applied to a Au(111) surface with atomically flat terraces in aqueous perchloric acid solutions. The pits, a single layer deep, were formed during the electrochemical reduction of oxide layers with higher oxidation states. The surface diffusion of Au atoms in a "pure" HClO sub 4 solution was quite slow and comparable to that observed in ultrahigh vacuum (UHV) reported in the previous literature. An electrochemical dissolution of Au was investigated in a HClO sub 4 solution in the presence of chloride ion. Strongly adsorbed chloride ions on Au(111) remarkably enhanced the surface diffusion of Au.