Formation of thiol-based monolayers on gold: implications from open circuit potential measurements

Abstract

The dynamics of the charge transfer process that transpires during the chemisorption of thiol-derived monolayers on gold electrodes have been examined by monitoring the temporal evolution of the open circuit potential (OCP). As a consequence of adlayer formation, the OCP shifts negatively. This shift is attributed to the accumulation of negative charge on the electrode through the donation of electron density from sulfur to gold. The magnitude of the shift, however, is much less than that estimated for a one-electron chemisorption process at an interface modeled simply as a parallel plate capacitor. Based on the findings of these and other experiments, we propose that the formation process involves both the oxidative deposition of the adlayer and the reduction of the sulfhydryl proton to hydrogen. Evidence consistent with these conclusions is presented.