Influence of the crystallographic orientation on the reductive desorption of self-assembled monolayers on gold electrodes

The voltammetric behaviour of the self-assembled monolayers formed by distinct types of thiolated molecules, namely decanethiol, 2-mercaptobenzimidazole-5-sulphonate (MBIS) and a thiolated DNA sequence was examined at polycrystalline gold electrodes and at the low-index faces Au(1 1 1), Au(1 0 0) and Au(1 1 0) as well as at Au(2 1 0). For the three thiol compounds, the multiwave voltammetric responses at polycrystalline are discussed on the basis of the behaviours observed at well-defined single-crystal electrodes. The sequence of reductive desorption (RD) potentials follows qualitatively the sequence of the potential of zero charge (pzc) of the uncovered electrodes in the case of MBIS. Such a sequence may be altered when attractive lateral interactions between adsorbed molecules, leading to an enhancement of the self-assembled monolayer stability, can be established. The RD peaks are therefore no longer simply directly related to the pzc of the substrate since the amplitude of lateral interactions depends on the atomic roughness of the substrate.