Single-Particle Investigation of Plexcitons in Bimetallic Nanorods

Abstract

Coupling between plasmons and excitons results in the emergence of novel spectroscopic features directed by the interaction energy, e.g., strong coupling results in the formation of new bands, whereas weak coupling leads to the enhancement of spectroscopic signals. The plasmon-exciton interaction energies are often determined at the ensemble level studies in solution by tuning and detuning the plasmonic resonance frequency. Herein, we present an efficient method for determining the dispersion curves and the Rabi splitting energy of chromophore-bound bimetallic core-shell Au-Ag nanorods by recording their single-particle scattering spectra using dark-field scattering spectroscopy/microscopy in two ways: by placing them on a glass slide and a micron-reference transmission electron microscope grid. The resonance frequency of the plasmonic system is varied by changing the thickness of the silver shell and investigating the coupling with the J-aggregates of 1,1′-diethyl-2,2′-cyanine iodide. The single-particle scattering spectra of bare Au@Ag NRs are conveniently recorded by removing the bound chromophore using methanol. The ensemble-level investigations provided similar dispersion curves and interaction energy, further confirming the reliability of the present method. Moreover, the DFM-TEM method presented herein provides a good correlation between the experimental scattering spectra and the theoretical scattering spectra obtained using finite-difference time-domain simulations.