Energy dependent Chemical Interface Damping induced by 1-Decanethiol Self-Assembled Monolayer on Au(111)

Abstract: The chemical interface damping (CID) effect increases the collision frequency of free electrons in metals by changes of the metal surface. We have now experimentally disentangled the two contributions to CID: induced roughness and direct charge transfer. The latter is an important area of research in photoelectrochemistry with potential applications in light-induced chemical reactions. We present a broadband investigation of the CID effect on Au(111) covered by a self-assembled monolayer of decanethiol. Spectroscopic ellipsometry measurements show a photon energy dependent increase of collision frequency. We observe a constant, photon energy independent contribution, which is attributed to induced roughness and a contribution that linearly increases with photon energy from about 1 eV upwards which we attribute to direct charge transfer. The onset of the charge transfer mechanism corresponds to occupied orbitals of thiols bound to the Au surface, as confirmed by density functional theory calculations.