Publication
We report on ultrafast transient absorption (TA) studies of surface plasmon-excited similar to 25 nm-diameter Au nanoparticles in solution, monitoring the response of the surface plasmon resonance in the visible region (1.7-3.0 eV) and that of the inter- and intraband transitions in the deep UV region (3.4-4.5 eV). The former reflects lattice heating by electron-phonon energy transfer, while the latter monitors charge carriers, that is, excess holes and electrons, respectively, below and above the Fermi level. Although the steady-state UV absorption spectrum of Au is featureless, the TA spectra reveal three bands that appear promptly upon plasmon excitation and decay over hundreds of picoseconds (ps). Based on the band structure diagram of bulk Au, we attribute symmetry points. The decay of the hot electrons monitored via the probing the intraband transitions at the L symmetry points below the latter requiring tens of ps. These results show that after the initial processes, hot charge carriers above and below the Fermi level remain of ps.