Voltammetric detection of the surface diffusion of adsorbed thiolate molecules in artificially phase-separated binary self-assembled monolayers on a Au(111) surface

Surface diffusion of adsorbed alkanethiolate molecules forming a binary sel f-assembled monolayer (SAM) on Au(111) has been studied by monitoring the c hange in the shape of voltammograms for the reductive desorption of adsorbe d thiolates. Artificially phase-separated SAMs of undecanethiol (UDT) and m ercaptoundecanoic acid (MUA), which would form homogeneously mixed binary S AMs at the thermodynamic adsorption equilibrium, are prepared starting from the phase-separated binary SAMs composed of mercaptopropionic acid (MPA) a nd UDT, followed by the electrochemical partial desorption of the MPA domai ns and successive adsorption of MUA from ethanol to the domains originally occupied by MPA molecules. The mutual dissolution of UDT and MUA on the gol d surface is monitored as the gradual merging of the initially well-separat ed two peaks on the voltammogram of reductive desorption of the thiolates. The average diffusion coefficient of adsorbed UDT and MUA at 60 degreesC in water is estimated to be about 10-18 cm(2) s(-1).