PASSIVATION OF PINHOLES IN OCTADECANETHIOL MONOLAYERS ON GOLD ELECTRODES BY ELECTROCHEMICAL POLYMERIZATION OF PHENOL

An organized monolayer of octadecanethiol on a gold electrode strongly inhibits faradaic reactions except at pinholes in the monolayer. For simple outer-sphere redox couples, the monolayer-coated electrode behaves like a microelectrode array, with pinholes acting as the microelectrodes. The average size and separation of the pinholes can be estimated by fitting the experimental cyclic voltammograms with simulated voltammograms for a microarray electrode. The pinholes are selectively and permanently passivated by electrochemical polymerization of phenol in dilute sulfuric acid. The deposition of poly-(phenylene oxide) suppresses the pinhole currents at low overpotential, but residual faradaic currents become visible at large overpotential. The residual currents are assigned to electron tunneling between the electrode and molecules which partially penetrate the monolayer. © 1990, American Chemical Society. All rights reserved.