Hot-Electron Dynamics and Thermalization in Small Metallic Nanoparticles

The important role played by hot electrons in photocatalysis and light harvesting has attracted great interest in their dynamics and mechanisms of generation. Here, we theoretically study the temporal evolution of optically excited conduction electrons in small plasmon-supporting gold and silver nanoparticles. We describe the electron dynamics through a master equation incorporating transition rates for optical excitations and electron–electron collisions that are calculated using the screened interaction within an independent-electron picture. Upon optical excitation of the particle by a light pulse, a nonthermal electron distribution is produced, which takes 10s fs to thermalize at an elevated electron temperature due to electron–electron collisions and eventually relaxes back to ambient temperature via coupling to phonons and thermal diffusion. Phonons and diffusion are introduced through a phenomenological inelastic attenuation rate. We find the temporal evolution of the electron energy distribution to strongly depend on the total absorbed energy, which is in turn determined by particle size, pulse fluence, and photon energy. Our results provide detailed insight into hot-electron dynamics that can be beneficial for the design of improved photocatalysis and photodetection devices.