Double-layer of the Au(111) electrodes modified by self- assembled monolayers of thiol with carboxyl terminal group: 3-D Poisson-Boltzmann method and Monte Carlo simulation

摘要

The self-assembled monolayer (SAM) of thiol with carboxyl group terminal on Au(111) has very strong electric double layer when the terminal group is dissociated in alkaline solution. The terminal carboxylate anions of the SAM on Au(111) form the regular periodic array and the surface charge density is ca. 0.74 C m~(-2) if the surface coverage of thiol is one third of the gold surface atoms. This strong double layer changed the capacitance of the system, and Finklea et al. reported that the electron transfer rate is increased for the SAM with the dissociated carboxy terminal, and the increase was explained by the electrostatic interaction between the carboxylate anion and the cation redox. Recently we have shown the increase can be explained by the Frumkin effect. To explain the capacitance change and the increase of the electron transfer rate theoretical studies on the three dimensional structure of the double layer may be necessary. In the present study we have carried out the theoretical study on the double layer structure by the three dimensional nonlinear Poisson-Boltzmann(PB) method and the canonical Monte-Calro simulation using the primitive model.