Structural evolution of self-assembled monolayer of 1-mercapto-2-propanol on Au(1 1 1) in a N 2 flow: an electrochemical and STM study

Abstract

The structural evolution of 1-mercapto-2-propanol layer on Au(1 1 1) during a treatment in a N 2 flow was investigated using STM and cyclic voltammetry. The pristine layer showed a striped structure of (2√3×√3) with coverage of 0.33. As the SAM was treated in the N 2 flow, the superlattice evolved sequentially and irreversibly to the structures of (√21×√3) and (√3×√3)R30° without any coverage change and ultimately to amorphous domains with coverage less than 0.33. In cyclic voltammetric studies, it was found that the coverage of 1-mercapto-2-propanol was 0.33 and that the N 2 treatment induced a partial desorption of the adsorbed thiol molecules. In addition to this, the reductive stripping potential shifted to the anodic direction, signaling that the SAM of 1-mercapto-2-propanol became unstable. The structural evolution and destabilization of the 1-mercapto-2-propanol layer on Au(1 1 1) was discussed in terms of the attractive force between the OH groups via hydrogen bonding and the repulsive force between the methyl groups.