An EQCM study of the oxidative deposition of alkylthiolates on gold

The oxidative deposition of alkylthiolates on a gold surface has been studied with the electrochemical quartz crystal microbalance (EQCM) method. The surface concentration of alkylthiolates calculated from the oxidative charge and from the EQCM signal using the Sauerbrey equation are in excellent agreement for depositions done in 0.1 M KOH and 0.1 M LiOH aqueous solutions. Potential step experiments allowed the measurement of the mass of alkylthiolates deposited versus time. These experiments show that the oxidative deposition of alkylthiolates occurs in two steps for slow deposition rates and in one step for fast deposition rates. The EQCM data of the oxidative deposition of alkylthiolates can be described by a combination of a potential dependent instantaneous nucleation-growth process and a potential independent Langmuir process. At faster deposition rates, the deposition occurs only by the nucleation and growth mechanism whereas at slower deposition rates up to one-third of a monolayer can be deposited via a Langmuir process.