Mapping near-field localization in plasmonic optical nanoantennas with 10 nm spatial resolution

Quantifying the near-field localization in plasmonic optical nanoantennas is fundamentally important to understand and optimize the design and fabrication of nanostructures for various applications. Here, the near-field localization in optical gap nanoantennas that are in resonance or near-resonance with 633 nm excitation wavelength is directly visualized in real space with 10 nm spatial resolutions, mapping the amplitude and phase characteristics of the in-plane and out-of-plane vector components selectively. While large field amplitude is observed in the gap for the in-plane component, the narrow gaps that are not resolved in the topographic image have been clearly observed in the optical images when the out-of-plane component is mapped, suggesting that the lateral optical resolution can surpass the radius of curvature of the probing tip. The effects of various structural parameters and metallic adhesion layer on the extent of field localization have been discussed, providing important insight in designing and fabricating plasmonic optical devices. (C) 2014 AIP Publishing LLC.