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

The dynamics of the charge transfer process that transpires during the chem isorption 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 shif t is attributed to the accumulation of negative charge on the electrode thr ough 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 ch emisorption process at an interface modeled simply as a parallel plate capa citor. Based on the findings of these and other experiments, we propose tha t the formation process involves both the oxidative deposition of the adlay er and the reduction of the sulfhydryl proton to hydrogen. Evidence consist ent with these conclusions is presented. (C) 1999 Elsevier Science S.A. All rights reserved.