Electrochemical oxidative adsorption and reductive desorption of a self-assembled monolayer of decanethiol on the Au(111) surface in KOH+ethanol solution

The electrochemical characteristics of an Au(111) electrode were investigated in 0.1 M KOH ethanol solutions containing various concentrations of decanethiol. Anodic and cathodic peaks corresponding to the oxidative adsorption and reductive desorption, respectively, of a self-assembled monolayer (SAM) of decanethiol were observed. Both peaks shifted negatively with an increase in the thiol concentration by ca. 57 mV/decade, showing that the redox process is a one-electron process. The adsorbed amount determined from the charge corresponding to the reductive desorption increased with an increase in the decanethiol concentration but never reached the saturated amount as long as the cyclic voltammograms were recorded continuously with a sweep rate of 10–200 mV s−1. The adsorption increased with the holding time at +0.1 V, which was much more positive than the anodic peak potential, and reached the saturated amount in ca. 10 min in a 10 μM thiol solution. The reductive peak potential also shifted negatively with the holding time but over a longer period. It continued to shift for ca. 60 min in the 10 μM thiol solution, which was much longer than the time taken for the adsorbed amount to reach the saturated value. These results suggest that the formation of a highly ordered SAM requires a much longer time than the adsorption of the thiol.