Gap-dependent optical coupling of single Bowtie nanoantennas resonant in the visible

Metallic bowtie nanoantennas consisting of two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm. For light polarized along the line between the two triangles, the plasmon scattering resonance first blue-shifts with increasing gap, and then red-shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size. This behavior may be approximately understood in a coupled-dipole approximation as changes in the phase between static dipole-dipole interactions and dipole radiative interaction effects.