Transient electron energy-loss spectroscopy of optically stimulated gold nanoparticles using picosecond pulsed electron beam

Abstract

Ultrafast phenomena in gold nanotriangles (AuNTs) were investigated using a transient electron energy-loss spectroscopy (TEELS) technique under irradiation from a 150-fs pulse laser with a wavelength of 780 nm. This investigation was conducted using a time-resolved transmission electron microscopy method that was developed to measure the dynamics of nanomaterials. Enhancement of the intensity and energy-width broadening of the energy loss were observed at the EEL peaks associated with surface and bulk plasmons on the AuNTs. The TEELS measurement revealed two decay processes of 7.8 ps and longer than 100 ps that compensate for relaxation times of excited surface plasmons using transient absorption spectroscopy. The results show that the bulk and surface plasmons have the same time evolution, i.e., that the excited electrons on the surface and in the bulk have the same relaxation processes in both electron-phonon and phonon-phonon interactions. The time evolution of electronic and lattice temperatures was also estimated based on the measured relaxation time using a two-temperature model, which revealed the volume expansion of the AuNTs and clarified the energy shifts of plasmons. Details of excited electrons in nanoparticles investigated via plasmon energy loss are expected to facilitate improvement in the performance for energy harvesting of photons in nanostructure-controlled materials.