Resolving Electron-Electron Scattering in Plasmonic Nanorod Ensembles Using Two-Dimensional Electronic Spectroscopy.

Jeffries, William R; Park, Kyoungweon; Vaia, Richard A; Knappenberger, Kenneth L · Nano Lett · 2020

basic_science · Level V

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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 Γ<sub>h</sub>(<i>t</i>), which was sensitive to changes in Fermi-level carrier densities. This approach was effective because electronic excitation accelerated plasmon dephasing, which broadened Γ<sub>h</sub>. Analysis of Γ<sub>h</sub>(<i>t</i>) indicated plasmon coherence times were decreased by 20-50%, depending on excitation conditions. Electron-electron scattering rates of approximately 0.01 fs<sup>-1</sup> were obtained by fitting the time-dependent Γ<sub>h</sub> 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 Γ<sub>h</sub> narrowing. To our knowledge, this is the first use of the plasmon Γ<sub>h</sub>(<i>t</i>) 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.