Ultrafast relaxation at electrochemical interfaces of alkanethiol-modified gold electrodes

Potential dependence of ultrafast electronic responses at Au electrode-solution interfaces was investigated by means of transient reflectivity measurements, in which co-axial pump-and-probe detection nas employed with a femtosecond laser and under electrochemical potential control. The interfaces of bare Au(111) and those modified with self-assembled monolayers of 1-dodecanethiol or 1-hexadecanethiol were investigated in aqueous solutions of perchloric 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 make the decay time constant increase in average as the hydrocarbon chain length increased, although different interfaces had different features of potential dependence. These results are discussed in connection with potential-dependent static and dynamic structures of solvents or adsorbed molecules on the interfaces.