Size-Dependent Electron-Phonon Coupling In Monocrystalline Gold Nanoparticles

Hot electrons in metal nanoparticles thermalize with the lattice via electron-phonon coupling. Size dependency is controversially discussed in literature. Here we investigate poly- and monocrystalline gold nanoparticles via transient absorption spectroscopy. As reported earlier, electron-phonon coupling in polycrystalline particles is not size-dependent. However, we clearly observe a size-dependent electron-phonon coupling in monocrystalline particles. Larger monocrystalline particles show slower electron-phonon coupling due to the decreasing effect of electron-surface scattering, with electron-phonon coupling constants approaching the values reported for bulk gold. In polycrystalline particles, size dependencies are outweighed by effective electron scattering at grain boundaries. Linear absorption spectra indicate that plasmon damping is also enhanced in polycrystalline particles by grain boundaries.