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.