Ultrafast electron dynamics at the liquid–metal interface: Femtosecond studies using surface plasmons in aqueous silver colloid

Abstract

We report direct femtosecond measurements of the dynamics of photoinduced electrons at the liquid–metal interface produced by exciting the surface plasmon band of aqueous silver colloidal particles. The electron plasma resonance created initially dephases into individually excited electrons in less than 150 fs. This is followed by a large component, fast exponential decay with a time constant of 2 ps, which is attributed to electronic energy relaxation through electron–phonon coupling. A slower 40 ps decay is also observed and attributed to subsequent cooling of the excited phonons due to phonon–solvent interaction. The decay dynamics, especially the 2 ps decay, are relatively insensitive to the solvent environment, indicating that the early time decay is dominated by the properties of the silver particles. The solvent molecules play an important role in the phonon cooling process following the electronic energy relaxation. The results show that the majority of the electrons created through photoexcitation of the plasmon band decay in less than 50 ps.