Highly Tunable Gold Nanorod Dimer Resonances Mediated Through Conductive Junctions

We study the optical properties of gold nanorod (Au NR) dimers connected end-to-end by a thin metallic junction. The plasmonic oscillations along the long axis of the dimer gives rise to two dominant modes: a bonding dimer plasmon emerging from the dipolar mode of each individual nanorod and a charge transfer plasmon involving the entire dimer structure. We find the charge transfer plasmon absorbance peak shift from the dimer structure is proportional to the NR aspect ratio (AR) behaving as it was a single NR with an AR nearly an order of magnitude larger. The charge transfer plasmon absorbance peak sensitively depends on the material and geometry of the connecting junction, theoretically tuning the absorbance peak from 1 mu m to 10 mu m. A straightforward "Drude-like" model to describe the charge transfer plasmon response is presented. The development of charge transfer plasmon nanostructures may open up new classes of plasmonic nanostructures leading to disruptive metamaterial technologies.