Electronic Properties of a Monolayer-Electrolyte Interface Obtained from Mechanistic Impedance Analysis

We report here a methodology to measure and characterize the interface properties of thin, insulating films that separate a gold electrode and an electrolyte solution, for cases when the electrolyte solution does not contain electro-active ions in appreciable amounts, by using experimental impedance data. Traditionally, in the absence of redox-active species either in the electrolyte or at the terminal headgroup, monolayer films on polycrystalline gold electrodes have been modeled as ideal dielectric capacitors. However, potential-dependent background currents are usually observed for gold−monolayer−electrolyte systems, even in the absence of redox-active moieties. A qualitative description of the background current density as a barrier-limited flux of charge that applies irrespective of the actual mechanism of charge transport through the monolayer film is proposed in this paper. The potential-dependent, low-frequency impedance data is shown to characterize the properties of this limiting energy barrier....

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