Adsorbate-mediated relaxation dynamics of hot electrons at metal/organic interfaces

Hot-electron dynamics at metal surfaces are crucial for charge transport properties and chemical reactions at metal/organic interfaces. In order to study the influence of electron-donating adsorbates on hot-electron lifetimes we performed femtosecond time-resolved two-photon photoemission measurements of tetrathiafulvalene (TTF)-covered Au(111) surfaces. The electron-donating nature of TTF provides density of states near the Fermi energy (${E}_{F}$) increasing the possibility for electron-electron scattering events. This leads to an additional fast electron-electron scattering assisted hot-electron relaxation channel for low intermediate state energies (${E}_{i}\ensuremath{-}{E}_{F}$) at the TTF/Au(111) interface with hot-electron lifetimes up to $340\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$. However, suppressing the electron donation via intercalation of electron-accepting tetracyanoquinodimethane molecules causes quenching of this fast electron relaxation channel. This results in an asymptotic increase of the hot-electron lifetimes for infinitesimal small intermediate state energies up to about $1000\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$ as predicted by the pure Landau theory of Fermi liquids.