Time-resolved spectral densities of non-thermal electrons in gold

TL;DR

This study presents a kinetic model for non-thermal electron dynamics in gold nanoparticles, revealing how excitation parameters influence spectral densities and relaxation times crucial for photocatalytic efficiency.

Contribution

It introduces a full energy-resolved Boltzmann collision integral approach to describe non-equilibrium electron distributions in noble metals, accounting for secondary electron generation and energy-dependent dynamics.

Findings

Electron relaxation times vary with kinetic energy.

Laser photon energy and fluence influence electron dynamics.

Time-dependent spectral densities differ from equilibrium values for picoseconds.

Abstract

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 are crucial for the efficiency of the photocatalysis and for the selective control of reactions. In this work, we present a kinetic description of the non-equilibrium 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 non-equilibrium and the inherently included secondary electron generation govern the dynamics of non-thermal electrons. Applying our method to gold, we show a significant dependence of hot electron dynamics on kinetic energy. Specifically, the timescales of the relaxation as well as the qualitative behavior are depending 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.