Fig. 2.

(A) Schematic of the ultrafast SERS experiment. We excite the LSPR using a pump pulse and observe molecular change at various time delays with a spontaneous SERS probe. (B) Representative ground state addition ultrafast SERS experimental spectra of MVCl${}_2$ on AuFON (10.6 W/cm${}^2$ pump, 13.6 W/cm${}^2$ probe). A mixed MV${}^0$/MV${}^{\bullet +}$ ground state population evolves after the LSPR excitation, where we observe an increase in the relative MV${}^0$ (green) : MV${}^{\bullet +}$ (blue) ratio. This change is proof of a plasmon-driven charge transfer from AuFON to MV${}^{\bullet +}$. (C) Overview of energy dissipation following LSPR excitation. After excitation, free electrons take on a nonequilibrium distribution of energies (10 to 100 fs). These electrons thermalize through electron–electron/electron–phonon scattering and interactions with nearby molecules (1 to 10 ps). Phonon excitation increases the lattice temperature, which eventually equilibrates with the bath (100+ ps).