In situ quartz-microbalance study of the self-assembly and stability of aliphatic thiols on polarized gold electrodes

Abstract

The kinetics of the self-assembly process of octadecanethiol from ethanolic electrolytes has been studied on gold electrodes. Two in situ methods have been employed simultaneously: the electrochemical quartz microbalance (EQMB) and the continuous measurement of the interfacial impedance. The state of the surface layers produced has been characterized further by measuring the charge-transfer rate between the modified electrode and a redox system in an aqueous electrolyte, and by measuring the potential-dependent impedance in aqueous electrolyte. It is concluded that, in the absence of oxidizing agents, the adsorption reaction of thiol on gold in the alcoholic electrolyte proceeds with formation of H₂. The healing process of the formed monolayer is completed only after ca. 15 h exposure of the electrode to the thiol solution. In the presence of oxidizing agents (in particular oxygen) the corresponding disulfide forms and deposits on top of a monolayer of good quality. In alcoholic electrolyte the film is stable in the range of applied electrode potentials 0.0 to –1.8 V vs. SCE.