Revealing Plasmonic Coupling of Gold Nanoparticles on a Mirror Using Spectromicroscopy

A spectro-microscopic system was developed that combines reflected dark field microscopy with total internal reflection scattering microscopy. This instrument also includes a high-resolution spectrometer for Raman Spectroscopy and photoluminescence spectroscopy measurements. This instrument was used to analyze single gold nanorods coupled to a gold film system to understand the light-matter interactions. It was found with total internal reflection scattering the single-particle spectroscopy is uniquely different than the scattering from the same particle illuminated with reflected dark field microscopy. This difference is due to the underlying coupling mechanisms between a gold nanorod and the thin gold film. Interestingly, by tuning the excitation polarization of total internal reflection scattering, the coupling modes are deconvoluted into multiple peaks which make up the broad scattering peaks. Finally, gold nanospheres coupled to layered two-dimensional materials were studied by reflected dark field scattering. The single particle scattering pattern evolves from a dot shape to a doughnut shape with increasing layers of material. This image evolution is related to the dielectric function of the material