Voltammetric Properties of the Reductive Desorption of Alkanethiol Self-Assembled Monolayers from a Metal Surface

Abstract

The current peak that appears on a linear-scan voltammogram for the reductive desorption of alkanethiol self-assembled monolayers (SAMs) from a gold surface in an aqueous alkaline solution exhibits intriguing features: the narrow full width at half-maximum (fwhm) of the peak, e.g., 20 mV for dodecanethiol SAMs, the saturation of fwhm in the SAM composed of long-chain alkanethiols, an asymmetric shape, the shift of the peak potential with increasing the alkyl chain length, and the peak area that is greater than what is expected from the (√3 × √3)R30° structure of adsorbed alkanethiols on Au(111). A Pade approximant expression for the adsorption isotherm proposed by Blum and Huckaby based on the two-dimensional Ising model, in combination with the semi-infinite linear diffusion of desorbed species, well explains these salient features of the reductive desorption behavior. The double-layer charging current can amount to one-third of the charge calculated from the area of the peak of the reductive desorption...