Electrochemical scanning tunneling microscopy study of the electrochemical behavior of naked and n-alkanethiol-modified Au(111) surfaces in F−- and CN−-containing electrolyte solutions

Abstract

We report an electrochemical scanning tunneling microscopy (ECSTM) study of CN−- and F−-induced etching of naked and n-alkanethiol-modified Au(111) surfaces. We use electrochemical methods to activate or deactivate etching of the Au surface, and we monitor changes in surface topography simultaneously using STM. In F−-containing electrolytes we have observed that the STM tip can induce surface–atom diffusion in the electrochemical environment thereby enhancing surface pitting, island growth, and step edge movement. At potentials more negative than −150 mV (vs Ag/AgCl) the tip selectively removes Au atoms from surface defects and enhances growth on terraces. Similarly, we have found that the STM tip can profoundly alter the CN−-induced dissolution rate of Au. On naked Au surfaces held at extreme negative potentials, no CN− etching of the surface occurs. However, at slightly more positive potentials the surface is homogeneously etched. At intermediate potentials the area under the scanning STM tip is selectively etched at positive tip biases, but at slightly more negative biases etching proceeds less rapidly in the scanned region. Finally, when the Au(111) surface is modified with a single self-assembled monolayer (SAM) of organomercaptan molecules, surface etching processes are dramatically attenuated regardless of the substrate potential or tip bias.