Effect of the charged state of gold substrates on the surface composition of two-component alkanethiol self-assembled monolayers

The surface composition of the binary self-assembled monolayer (SAM) of 1-tetradecanethiol and 3-mercapto-1-propanol on gold varies with the charged state of the gold substrate because of the difference in the reductive desorption potentials of the two thiol species. This is a direct corollary of the finding by Paik et al. [S. Eu, W.K. Paik, Chem. Lett. 16 (1998) 405-406.] that the adsorption of thiols to a metal surface from the solution phase leads to the accumulation of negative charges on the surface. By controlling the potential of the gold substrate during the formation of a binary SAM, it is possible to change the surface composition. The saturation of the bathing ethanol solution with oxygen and the grounding of the substrate during the formation of the SAM have basically the same effect on the surface composition, as both mitigate the charge-up problem.