Near-field optical response of periodically arrayed plasmonic nanogap antennas

We have studied two-dimensional periodically arrayed plasmonic nanogap antennas that exploit a “resonant coupling effect,” efficiently collecting incident light and enhancing the nanogap field. A theoretical investigation was carried out on an infinite array of gold nanoblock dimers in a square-lattice arrangement. Under resonant conditions, the near-field intensity spectra in the gap region showed a narrow peak (full width at half maximum of 50 nm) with a field enhancement that was a factor of ∼5 stronger than that of an isolated single-nanogap antenna. The influence of the geometrical parameters of the array (period, dimer orientation, nanogap size, and number of periods) is discussed.