Field enhancement and gap-dependent resonance in a system of two opposing tip-to-tip Au nanotriangles

The enhancement of the electromagnetic field is described for nanoscale metallic ``bowtie'' antennas, consisting of two opposing tip-to-tip Au nanotriangles separated by a gap, through simulation and experiment. Currents, field distributions, and scattering efficiencies in the antennas at optical wavelengths are obtained from finite-difference time-domain (FDTD) simulations using realistic wavelength-dependent dielectric constants. The experimentally measured resonant wavelengths and intensity enhancements from individual bowtie antennas are in excellent agreement with the FDTD simulations. A simple physical model based on current distribution in the antennas is presented to understand the variation in resonant wavelength with gap and explain the basis for the field enhancement.