Nanoimprint fabrication of gold nanocones with ~10 nm tips for enhanced optical interactions

Optoelectronics Research Centre, Tampere University of Technology, Department of Physics, Optics Laboratory, Tampere, Finland.
Optics Letters (Impact Factor: 3.18). 08/2009; 34(13):1979-81. DOI: 10.1364/OL.34.001979
Source: PubMed

ABSTRACT We show that nanoimprint lithography combined with electron-beam evaporation provides a cost-efficient, rapid, and reproducible method to fabricate conical nanostructures with very sharp tips on flat surfaces in high volumes. We demonstrate the method by preparing a wafer-scale array of gold nanocones with an average tip radius of 5 nm. Strong local fields at the tips enhance the second-harmonic generation by over 2 orders of magnitude compared with a nonsharp reference.

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Available from: Janne Simonen, Jul 28, 2015
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    • "They may serve, for example, as anchor points for electro-optic active molecules, used for electrooptical devices. Usually, metal nanoparticle arrays are prepared by electron beam lithography [53] [54] [55] or photolithography [56] [57]. While electron beam lithography is time consuming and expensive, photolithography has lower limits concerning nanoparticle size. "
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    ABSTRACT: ewas used to characterize a nanocone-tip antenna [3]. Here, we show that second harmonic generation (SHG) imaging using cylindrical vector beams permits highly sensitive mapping of the local response in a gold nanocone array. Our sample consists of gold nanocones on a silicon substrate fabricated using UV-nanoimprint lithography [4]. The nanocones, each having a base diameter of 150 nm and 10 nm tip radius, are arranged in a square array with a cone-cone period of 1000 nm (Inset of Fig. 1 a). Previously, similar nanocones have been shown to exhibit very strong SHG signals when excited by radially polarized light [4]. To characterize the nanocones, we used a custom-built stage-scanning epi-SHG microscope equipped with a femtosecond laser (1060 nm, 200 fs, 82MHz), a 0.8 NA objective lens, appropriate optical filters and a single-photon counting module. We utilized a liquid crystal converter (Arcoptix) to change the polarization mode of the incident beam from radial to azimuthal. To investigate the local field enhancement in the array of gold nanocones, we measured the SHG signal as a function of average input power of the focused radially polarized light. As shown in Fig. la, the SHG signals from the nanocones vary quadratically with the input laser power. This nonlinear sensitivity implies that the nanocones are strongly influenced by the longitudinal component of the focused radially polarized light.
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