Ultrafast relaxation at electrochemical interfaces of alkanethiol-modifiedgold electrodes

Potential dependence of ultrafast electronic responses at Au electrode-solu tion interfaces was investigated by means of transient reflectivity measure ments, in which co-axial pump-and-probe detection nas employed with a femto second laser and under electrochemical potential control. The interfaces of bare Au(111) and those modified with self-assembled monolayers of 1-dodeca nethiol or 1-hexadecanethiol were investigated in aqueous solutions of perc hloric or sulfuric acid. A single exponential decay component was observed in each sample system. The decay time constants determined were ranged from 100 to 300 fs and were dependent on the potential, interface modification, and electrolyte in the solution. The interface modification was found to m ake the decay time constant increase in average as the hydrocarbon chain le ngth increased, although different interfaces had different features of pot ential dependence. These results are discussed in connection with potential -dependent static and dynamic structures of solvents or adsorbed molecules on the interfaces.