Pfeiffer, MauriceMauricePfeifferVonbun-Feldbauer, GregorGregorVonbun-FeldbauerKhurgin, Jacob B.Jacob B.KhurginMatts, OlgaOlgaMattsShqer, AhmedAhmedShqerMameka, NadiiaNadiiaMamekaEich, ManfredManfredEichPetrov, AlexanderAlexanderPetrov2026-03-092026-03-092026-02-11Journal of Physical Chemistry C 130 (8): 3096-3101 (2026)https://hdl.handle.net/11420/61917The chemical interface damping (CID) effect increases the collision frequency of free electrons in metals by changes to 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 the 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 upward, which we attribute to direct charge transfer. The onset of the charge transfer mechanism corresponds to the occupied orbitals of thiols bound to the Au surface, as confirmed by density functional theory calculations.en1932-74552026830963101Soc.Charge transferCollisionsGoldInterfacesThiolsNatural Sciences and Mathematics::530: PhysicsTechnology::620: Engineering::620.1: Engineering Mechanics and Materials Science::620.11: Engineering MaterialsJournal Article10.1021/acs.jpcc.5c07634Journal Article