The effect of concentration on the oxidative deposition of a monolayer of alkylthiolate on gold: from island formation to random adsorption

We report a study of the oxidative adsorption of butanethiolate on gold from solutions of butanethiolate ranging from 4 × 10−3 to 7 × 10−6 M. The mechanism of oxidative adsorption is found to be a function of the concentration of butanethiolate. At concentrations higher than approximately 7 × 10−4 M, cyclic voltammetry and EQCM measurements suggest that the oxidative adsorption proceeds via a fast nucleation and growth mechanism and a slow Langmuir mechanism. In-situ FTIR shows that the resulting monolayer of butanethiolate is organized. The oxidative adsorption from solutions of butanethiolate with a concentration lower than approximately 7 × 10−5 M is found to be slower and to proceed via a two-step Langmuir mechanism as a result of becoming diffusion-limited. In this case, the in-situ FTIR measurements show that a more disordered monolayer of butanethiolate is obtained. We suggest that the sudden change in the organization of the butanethiolate monolayer is related to the presence of micelles at higher concentration.