Potential-assisted deposition of mixed alkanethiol self-assembled monolayers

Preparation of self-assembled monolayers (SAMs) usually involves passive incubation. The recently developed potential-assisted deposition is indeed more selective as well as 100-fold faster than passive adsorption, thereby enhancing the reproducibility of the monolayer deposition.This article aims to identify the electrodeposition conditions necessary to prepare mixed alkanethiol SAMs on gold surface. Parameters such as concentrations in solution, electrode polarization and deposition time were examined for two chain lengths, C3 (mercaptopropionic acid, MPA) and C18 (octadecanethiol, ODT). The kinetics and composition of the SAMs were systematically characterized by reductive stripping analysis and by surface plasmon enhanced ellipsometry. Control of the surface concentration of the stable binary SAM was achieved by carefully adjusting the MPA fraction at between 70% and 95% in the deposition solution. Three theoretical models were developed. For MPA or ODT SAMs, whatever the adsorbate and the time period, the second order model gives the best fit. For the binary monolayer (MPA–ODT), a co-adsorption model was developed to describe the kinetics before 10 s.