Resolving Electron–Electron Scattering in Plasmonic Nanorod Ensembles Using Two-Dimensional Electronic Spectroscopy
William R. Jeffries, Kyoungweon Park, Richard A. Vaia, Kenneth L. Knappenberger
Abstract
The use of two-dimensional electronic spectroscopy (2DES) to study electron–electron scattering dynamics in plasmonic gold nanorods is described. The 2DES resolved the time-dependent plasmon homogeneous line width Γh(t), which was sensitive to changes in Fermi-level carrier densities. This approach was effective because electronic excitation accelerated plasmon dephasing, which broadened Γh. Analysis of Γh(t) indicated plasmon coherence times were decreased by 20–50%, depending on excitation conditions. Electron–electron scattering rates of approximately 0.01 fs–1 were obtained by fitting the time-dependent Γh broadening; rates increased quadratically with both excitation pulse energy and frequency. This rate dependence agreed with Fermi-liquid theory-based predictions. Hot electron thermalization through electron–phonon scattering resulted in Γh narrowing. To our knowledge, this is the first use of the plasmon Γh(t) to isolate electron–electron scattering dynamics in colloidal metal nanoparticles. These results illustrate the effectiveness of 2DES for studying hot electron dynamics of solution-phase plasmonic ensembles.