Scanning Tunneling Microscopy and Cyclic Voltammetry Study of Self-Assembled 3,3′-Thiobis(1-propanesulfonic acid, sodium salt) Monolayers on Au(111) Electrodes

Self-assembled monolayers (SAMs) of 3,3′-thiobis(1-propanesulfonic acid, sodium salt) (TBPS) on Au(111) electrodes have been characterized by scanning tunneling microscopy and cyclic voltammetry in aqueous perchloric acid solutions. TBPS exhibits an adsorption behavior typically observed for dialkyl sulfides including intact adsorption and low coverage phases with molecules predominantly lying flat on the surface. On the other hand, an untypical chemical bond and well-ordered domains were determined which resemble the characteristics of alkenethiol SAMs. When the adlayer was prepared at its open circuit potential (OCP), a (6 × 3√3) TBPS adlayer phase was observed at potentials E > 0.7 VRHE in TBPS-free electrolyte. At more cathodic potentials, the adlayer transforms irreversible to a disordered phase. In contrast, in situ STM studies in TBPS-containing electrolyte reveal a very complex, potential-dependent adsorption behavior. With increasing electrode potential, the structure of the adlayer transforms in...