Tunable chiro-optical effects in self-assembled metasurfaces: experiments, simulations, and perspectives

The nanoscale community has proposed various nanostructures for the enhancement of near- and far-field chiro-optical effects. Here we study such effects in asymmetric metasurfaces which can be produced by means of nanosphere lithography (NSL). NSL, combined with tilted plasmonic deposition, is a versatile, self-assembling method for fabrication of different asymmetric nanogeometries. Polystyrene nanospheres (PSN) are first self-assembled on glass, then reduced in diameter, and subsequently covered with a plasmonic layer. By controlling fabrication parameters, we can obtain three types of samples. First sample is based on PSN asymmetrically covered by metal under 45deg. This sample has a high contribution of the plasmonic elliptical nanohole array on the glass. Second sample is a plasmonic elliptical nanohole array obtained by simply removing the PSN from the first sample. Third sample is obtained by increasing the metallic deposition angle to 60deg; this way, nanohole array contribution vanishes, and the metasurface is based on asymmetric plasmonic nanoshells. We report on numerical studies on these three samples, when excited by oblique left or right circular polarization in the near-infrared range. The simulations are in good agreement with previously obtained experimental results, which gives a route to possible optimization of fabrication parameters for different applications. Finally, we comment on the follow-up application for each geometry. We believe that this technique can be used to produce high quality and low-cost substrates for chiral sensing; moreover, with the inclusion of near-field light emitting layer, these metasurfaces could lead to tunable circularly polarized visible or near-infrared light emission.