Studies of the electrochemical removal and efficient re-formation of a monolayer of hexadecanethiol self-assembled at an Au(111) single crystal in aqueous solutions

The electrochemistry of a hexadecanethiol monolayer deposited on a Au(111) single crystal electrode has been examined in electrolyte solutions of different pH values, and it has been found that a significant fraction of the hexadecanethiol monolayer can be electrochemically removed and redeposited repetitively from the Au(111) surface. We suggest that this behavior is caused by the low solubility of the reduced molecules which prevents their diffusion into the bulk of the solution. The solubility of the thiol is confirmed to be a most important factor in the oxidative redeposition process by identical experiments performed on butanethiol and nonanethiol layers which show a decrease in the oxidative redeposition with the increasing solubility of the thiol. Preliminary work suggests that surface roughness may also play a part in influencing the extent of oxidative redeposition, with smoother surfaces giving more redeposition. The reductive desorption/oxidative redeposition of hexadecanethiols in an aqueous solution of high pH (0.5 M KOH) consists of two distinct processes. This is suggested to arise from the presence of domains of thiols of different ionic permeabilities.