Energy-Resolved Femtosecond Hot Electron Dynamics in Single Plasmonic Nanoparticles

Efficientexcitation and harvesting of hot carriers from nanoscalemetals is central to many emerging photochemical, photovoltaic, andultrafast optoelectronic applications. Nevertheless, direct experimentalevidence of the energy-dependent femtosecond dynamics in ubiquitoustens-of-nanometer gold structures remains elusive, despite the potentiallyrich interplay between interfacial and internal plasmonic fields,excitation distributions, and scattering processes. To explore theeffects of nanoscale structure on these dynamics, we employ simultaneoustime-, angle-, and energy-resolved photoemission spectroscopy of singleplasmonic nanoparticles. Photoelectron velocity and electric fielddistributions reveal bulk-like ballistic hot electron transport indifferent geometries, lacking any signatures of surface effects. Energy-resolveddynamics are measured in the 1-2 eV range and extrapolatedto lower energies via Boltzmann theory, providing a detailed viewof hot electron lifetimes within nanoscale gold. We find that particleswith relevant dimensions as small as 10 nm serve as exemplary platformsfor studying intrinsic metal dynamics.