Multipolar Plasmonic Resonances in Silver Nanowire Antennas Imaged with a Subnanometer Electron Probe

We detect short-range surface plasmon-polariton (SR-SPP) resonances setup in individual silver nanoantenna structures at high-spatial resolution with a scanning, subnanometer electron probe. Both even and odd multipolar resonant modes are resolved up to sixth order, and we measure their spatial distribution in relation to nanoantenna structures at energies down to 0.55 eV. Fabry-Perot type SR-SPP reflection phase shifts are calculated from direct measurements of antinode spacings in high-resolution plasmonic field maps. We observe resonant SR-SPP antinode bunching at nanoantenna terminals in high-order resonant modes, and antinode shifts in nonhomogeneous local environments. Finally, we achieve good agreement of our experimental SR-SPP maps with numerical calculations of photon excited near fields, using a novel integrated photon excitation geometry.