Electrochemical Imaging of Surfaces and Adsorbates at the Atomic-Scale

            Electrochemical Scanning Tunneling Microscopy (EC-STM) is a useful technique as it operates under ambient conditions while providing atomic and molecular resolution of a surface. The pressure and temperature gaps can be bridged because in an electrochemical cell, the sample voltage can be cycled allowing for surface cleanliness at the atomic-level. Once the surface is clean, it is possible to add molecules to the electrolyte and then image the resultant surface assembly. Chiral molecule adsorption on achiral surfaces, like Au(111), is of particular interest as one can turn a flat achiral surface into a chiral one by molecular templating. In addition, the deposition of metal to create metal alloys on the surface can be used to alter the electronic state of the surface. This allows one to convert an inert surface like Au(111) into a more catalytically active surface without the problems associated with working with large reactive metal electrodes.

           Underpotential deposition (UPD) is a useful way of depositing up to one monolayer of a metal onto a more noble metal. We used this technique to deposit Ag onto Au(111) with and without the presence of chloride. Electrochemical scanning tunneling microscopy (EC-STM) revealed that, depending on the sample potential and hence the surface Ag coverage, Ag grows in a variety of structures that can be atomically resolved. However, upon being removed from the electrochemical cell, these Ag monolayers are subject to degradation by air. However, if the Ag layer is formed in the presence of trace amounts of chloride, the resulting AgCl layer is stable in air and even at elevated temperatures.