Electrochemical Oxidative Adsorption and Reductive Desorption of the Self-Assembled Monolayer of Decanethiol on 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 negatively shifted with the 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 continuously recorded with the sweep rate of 10 – 200 mV s-1. It 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 the 10 μM thiol solution. The reductive peak potential also negatively shifted with the holding time but for a longer period. It kept shifting for ca. 60 min in the 10 μM thiol solution, which is much longer than the time when the adsorbed amount reached 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.