Abstract
Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results and further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. This provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.
Highlights
Plasmonic nanoantennas that facilitate strong electromagnetic resonances in ultra-small mode volumes[1] can enhance light-matter interactions[2,3,4,5] but can tailor the emission or scattering patterns of quantum emitters coupled to them6–9
A reasonably strong g-nanocrystal quantum dots (NQDs)-antenna coupling can be achieved by adjusting patch sizes and dielectric layer thicknesses so that the eigen-wavelength of fundamental mode would be in resonance with the emission wavelength of g-NQDs
The fabrication process involves sputtering of 120 nm thick Au layer onto a cleaned fused silica substrate followed by spin coating of a ~200 nm thick PMMA (950 A4) film to define the lateral dimensions of the patches by e-beam lithography
Summary
Nanocrystal Quantum Dots to received: 13 April 2015 accepted: 25 August 2015 Published: 23 September 2015 the Fundamental Mode of Patch Nanoantennas through Fringe Field. Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. The two-step e-beam lithography requires a lithography system possessing sub-10 nm alignment precision for reliable large-scale applications To overcome this issue, vertically aligned patch nanoantennas, in which an ultra-thin dielectric layer is sandwiched between a metallic nano-patch and a metal layer, have been recently proposed[18,19]. A reasonably strong g-NQD-antenna coupling can be achieved by adjusting patch sizes and dielectric layer thicknesses so that the eigen-wavelength of fundamental mode would be in resonance with the emission wavelength of g-NQDs
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