Adsorption of a quaternary ammonium surfactant on Au(1 0 0)

The adsorption of a quaternary ammonium surfactant (octyltrimethylammonium triflate, OTATf) on Au(1 0 0) has been studied using cyclic voltammetry and chronocoulometry. The adsorption of the cationic surfactant does not lift either the thermal or charge-induced Au(1 0 0)-5 × 20 reconstruction. The adsorption of OTATf has also been studied on the unreconstructed, Au(1 0 0)-1 × 1, surface. Both crystallographic surfaces demonstrate similar behaviour characterized by a single state of adsorption yielding a positive shift in the potential of zero charge, Epzc. No evidence of ion-pairing is observed on these very negatively charged surfaces. Unlike similar zwitterionic and anionic surfactants the measured Gibbs surface excesses for OTATf indicate that this cationic surfactant does not aggregate into hemi-micelle structures on Au(1 0 0). A slightly higher capacity and a smaller positive shift in the Epzc is observed for the organic film formed on the unreconstructed surface compared to the reconstructed surface which indicates subtle differences in the two states of adsorption. On a rational potential scale, OTATf adsorbs on the Au(1 0 0)-5 × 20 surface at more negative potentials. This indicates that there is a stronger specific interaction between the aliphatic quaternary ion and the reconstructed substrate.