Ultrafast third-harmonic spectroscopy of single nanoantennas fabricated using helium-ion beam lithography

H. Kollmann; M. Esmann; S. F. Becker; X. Piao; C. Huynh; L.-O. Kautschor; G. Bösker; H. Vieker; A. Beyer; A. Gölzhäuser; N. Park; M. Silies; C. Lienau

doi:10.1117/12.2212689

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14 March 2016 Ultrafast third-harmonic spectroscopy of single nanoantennas fabricated using helium-ion beam lithography

H. Kollmann, M. Esmann, S. F. Becker, X. Piao, C. Huynh, L.-O. Kautschor, G. Bösker, H. Vieker, A. Beyer, A. Gölzhäuser, N. Park, M. Silies, C. Lienau

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Proceedings Volume 9759, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics IX; 975908 (2016) https://doi.org/10.1117/12.2212689
Event: SPIE OPTO, 2016, San Francisco, California, United States

Abstract

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, M. Esmann, S. F. Becker, X. Piao, C. Huynh, L.-O. Kautschor, G. Bösker, H. Vieker, A. Beyer, A. Gölzhäuser, N. Park, M. Silies, and 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); https://doi.org/10.1117/12.2212689

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