14 March 2016 Ultrafast third-harmonic spectroscopy of single nanoantennas fabricated using helium-ion beam lithography
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Metallic nanoantennas are able to spatially localize far-field electromagnetic waves on a few nanometer length scale in the form of surface plasmon excitations 1-3. Standard tools for fabricating bowtie and rod antennas with sub-20 nm feature sizes are Electron Beam Lithography or Ga-based Focused Ion Beam (FIB) Milling. These structures, however, often suffer from surface roughness and hence show only a limited optical polarization contrast and therefore a limited electric field localization. Here, we combine Ga- and He-ion based milling (HIM) for the fabrication of gold bowtie and rod antennas with gap sizes of less than 6 nm combined with a high aspect ratio. Using polarization-sensitive Third-Harmonic (TH) spectroscopy, we compare the nonlinear optical properties of single HIM-antennas with sub-6-nm gaps with those produced by standard Ga-based FIB. We find a pronounced enhancement of the total TH intensity of more than three in comparison to Ga-FIB antennas and a highly improved polarization contrast of the TH intensity of 250:1 for Heion produced antennas 4. These findings combined with Finite-Element Method calculations demonstrate a field enhancement of up to one hundred in the few-nanometer gap of the antenna. This makes He-ion beam milling a highly attractive and promising new tool for the fabrication of plasmonic nanoantennas with few-nanometer feature sizes.
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H. Kollmann, H. Kollmann, M. Esmann, M. Esmann, S. F. Becker, S. F. Becker, X. Piao, X. Piao, C. Huynh, C. Huynh, L.-O. Kautschor, L.-O. Kautschor, G. Bösker, G. Bösker, H. Vieker, H. Vieker, A. Beyer, A. Beyer, A. Gölzhäuser, A. Gölzhäuser, N. Park, N. Park, M. Silies, M. Silies, C. Lienau, C. Lienau, "Ultrafast third-harmonic spectroscopy of single nanoantennas fabricated using helium-ion beam lithography", Proc. SPIE 9759, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics IX, 975908 (14 March 2016); doi: 10.1117/12.2212689; https://doi.org/10.1117/12.2212689

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