Control of Electric Field Localization by Three-Dimensional Bowtie Nanoantennae

The three-dimensional morphological control of the individual metallic nanocrystals in a coupled structure imposes an electric field localization and enhancement in all three dimensions. We exploit the unique morphology of chemically synthesized nanotriangle monomers to form assembled dimers with a bowtie-like morphology in two orthogonal planes, effectively minimizing the volume of the interaction space to a point. The antenna has a longitudinal mode at 893 nm (1.39 eV), a 294 nm (0.68 eV) red shift compared to a monomer of equivalent size. This is indicative of extremely strong coupling because of the three-dimensional confinement of the electric field within the nanogap. By changing the geometry of the nanotriangle dimer, the longitudinal mode is tunable within a 220 nm (0.45 eV) range. The distribution of the electric field in the interparticle space transitions from a localized point for a bowtie to a more distributed line for an inverted bowtie.