Arrays of suspended plasmonic nanodiscs

Abstract

Abstract:We demonstrate lateral arrays of suspended metal nanodiscs, erected in parallel, partially encased in a dielectric-wrap using in-template synthesis with their polarization-dependent properties controlled as a function of disc-gap/-width tailoring their scattering/absorption spectra.Plasmonic structures enable enhanced light utilization for optoelectronic devices owing to their unique, strong and tunable electric field localization leading to increased scattering and absorption properties. Various nanopatterned plasmonic structures have been proposed to date, which typically use the nanofabrication method of electron beam lithography (EBL). Although these techniques offer high resolution and allow for a more deterministic nanostructure layout for plasmonics, these technologies are quite costly and limited in high throughput. Alternatively, solution processed nanostructures have emerged, for example, including nanodiscs [1], which are synthesized using intemplate electro-deposition [2], followed by simple selective etching of sacrificial metal layers. These nanodiscs are promising for nanoplasmonics because their optical properties may be fine-tuned either via the disc-gap or the discwidth, which can range from 20 nm to several hundred nanometers. In this work, we demonstrate lateral arrays of Au nanodiscs with controlled gaps and widths using the in-template synthesis to allow for the tailoring of the scattering and absorption properties. This has resulted in massive numbers of easily and inexpensively fabricated arrays of nanodisc structures. The achievable resolution of our fabrication approach reaches down to approximately 20 nm. Fabricating such three-dimensional suspended and liquid dispersible architectures is not easily possible by other techniques such as EBL. Here, we report the plasmonic properties of these suspended nanodisc structures including the polarization-dependent scattering spectra computed numerically and measured experimentally. We study the polarization dependent absorption and scattering properties of the nanodisc arrays presented in Fig. 1(a) and 1(b). We model our discs to tailor the light spectra scattered from and absorbed in these Au discs with varying disc-widths (w) for different disc gaps (g). Under unpolarized illumination incident on discs, we observe different spectral contributions from the field polarized in vertical and horizontal directions. Figs. 2(b) and 2(c) present the computed quality scattering factors of the nanodisc array via power fraction analysis of vertically and horizontally polarized fields. Here the disc diameter (D) is 250 nm, which is set by our template membrane used during electro-deposition. When we compute the power component normal to the discs (vertical), we observe strong plasmonic coupling depending on the gap size (g) between the discs. The electric field localized between the discs is found to increase with this coupling. We observe a scattering peak at shorter wavelengths in Fig. 2(b) with a disc width (w) of approximately 50 nm and abov...