Direct Observation of Two-Dimensional Electron Solvation at Alcohol/Ag(111) Interfaces

Abstract

Time-resolved two-photon photoemission was used to investigate the two-dimensional electron solvation by methanol, 1-propanol, 1-butanol, and 1-pentanol overlayers on a Ag(111) surface. For each system at coverages higher than one monolayer, several image potential state series with time-dependent energies were observed by using two-photon photoemission indicating that multiple time-dependent local work functions can originate from multiple coverages. The time-dependent energy relaxation seen is attributed to the rotation of the adsorbate molecular dipoles to solvate the electron. This rotation lowers the electron-layer interaction energy, causing a dynamic reduction of the local work function which is a signature of the solvation of the electron by the adsorbate layer. A classical electron-disk dipole model supports the conclusion that the dynamic variation in the image potential state energies results from a local work function effect and indicates that the evolution of the energy results from the time-dependent projection of the molecular dipole onto the surface normal on the femtosecond time scale.