Abstract
Abstract A combination of helium- and gallium-ion beam milling together with a fast and reliable sketch-and-peel technique is used to fabricate gold nanorod dimer antennas with an excellent quality factor and with gap distances of less than 6 nm. The high fabrication quality of the sketch-and-peel technique compared to a conventional ion beam milling technique is proven by polarisation-resolved linear dark-field spectromicroscopy of isolated dimer antennas. We demonstrate a strong coupling of the two antenna arms for both fabrication techniques, with a quality factor of more than 14, close to the theoretical limit, for the sketch-and-peel–produced antennas compared to only 6 for the conventional fabrication process. The obtained results on the strong coupling of the plasmonic dimer antennas are supported by finite-difference time-domain simulations of the light-dimer antenna interaction. The presented fabrication technique enables the rapid fabrication of large-scale plasmonic or dielectric nanostructures arrays and metasurfaces with single-digit nanometer scale milling accuracy.
Highlights
Plasmonic nanostructures such as metallic nanoantennas act as functional elements in a wide range of applications
We find a significant red shift of the longitudinally polarized SPR (LSPR) of more than 150 nm for gap sizes of down to 5 nm accompanied with an outstanding quality factor of up to 14, proving the fabrication of low-loss plasmonic nanoresonators with performances approaching the theoretical limit
We find an enormous red shift for the sketch and peel”–based FIB milling (SaP)-produced dimers of more than δλ/λ0 = 0.31, larger than those reported for chemically synthesized nanorods [58] and those fabricated using electron-beam lithography (EBL) [59]
Summary
Plasmonic nanostructures such as metallic nanoantennas act as functional elements in a wide range of applications. The ion bombardment can lead to an undesired implantation of helium at the substrate–metal interface [51] To overcome this issue, Chen et al [52] introduced a simple, fast, and reliable fabrication technique called “sketch and peel”–based FIB milling (SaP). We further optimize this approach and propose a combination of Ga-FIB, for the rough outlining, with He-FIB lithography, for the precise fabrication of the gap region of the dimer antenna, together with the SaP technique for the lift-off process. By using this combination, a reduction of the minimum gap size of down to 5 nm was achieved. This technique enhances the current capability of FIB lithography for the fabrication of metallic structures and can bring the fabrication of large structures or large arrays of nanostructures with nanometer precision in a resistless and solvent-free way into reach
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