Journal
NEW JOURNAL OF PHYSICS
Volume 17, Issue -, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1367-2630/17/6/063010
Keywords
nano-optics; optical field enhancement; plasmon resonance; lightning rod effect; nanotips
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Funding
- Gordon and Betty Moore Foundation
- ERC
- FWF (Austria)
- International Max Planck Research School of Advanced Photon Science
- [SFB-041 ViCoM]
- [SFB-049 Next Lite: DK-1243 Solid4Fun]
- [P21141-N16]
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We theoretically investigate the dependence of the enhancement of optical near-fields at nanometric tips on the shape, size, and material of the tip. We confirm the strong dependence of the field enhancement factor on the radius of curvature. In addition, we find a surprisingly strong increase of field enhancement with increasing opening angle of the nanotips. For gold and tungsten nanotips in the experimentally relevant parameter range (radius of curvature >= 5 nm at 800 nm laser wavelength), we obtain field enhancement factors of up to similar to 35 for Au and similar to 12 for W for large opening angles. We confirm this strong dependence on the opening angle for many other materials featuring a wide variety in their dielectric response. For dielectrics, the opening angle dependence is traced back to the electrostatic force of the induced surface charge at the tip shank. For metals, the plasmonic response strongly increases the field enhancement and shifts the maximum field enhancement to smaller opening angles.
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