Time-Resolved Spectral Densities of Nonthermal Electrons in Gold

Noble-metal nanoparticles for photocatalysis have become a major research object in recent years due to their plasmon-enhanced strong light-matter interaction. The dynamics of the hot electrons in the noble metal is crucial for the efficiency of the photocatalysis and for the selective control of reactions. In this work, we present a kinetic description of the nonequilibrium electron distribution created by photoexcitation based on full energy-resolved Boltzmann collision integrals for the laser excitation as well as for the electron-electron thermalization. The laser-induced electronic nonequilibrium and the inherently included secondary electron generation govern the dynamics of nonthermal electrons. Applying our method to gold, we show a significant dependence of hot electron dynamics on the kinetic energy. Specifically, the time scales of the relaxation as well as the qualitative behavior are dependent on the evaluated energy window. During the thermalization processes, there are cases of increasing electron density as well as of decreasing electron density. Studying the influence of excitation parameters, we find that the photon energy and the fluence of the exciting laser can be tuned to influence not only the initial excitation but also the subsequent characteristics of the time-resolved electronic spectral density dynamics. The electronic thermalization including secondary electron generation leads to time-dependent spectral densities, which differ from their specific final equilibrium values for picoseconds after irradiation ended.