Plasmonic color generation and refractive index sensing with three-dimensional air-gap nanocavities

Towards scalable plasmonic Fano-resonant metasurfaces for colorimetric sensing

Transitioning plasmonic metasurfaces into practical, low-cost applications requires meta-atom designs that focus on ease of manufacturability and a robustness with respect to structural imperfections and nonideal substrates. It also requires the use of inexpensive, earth-abundant metals such as Al for plasmonic properties. In this study, we focus on combining two aspects of plasmonic metasurfaces-visible coloration and Fano resonances-in a morphology amenable to scalable manufacturing. The resulting plasmonic metasurface is a candidate for reflective colorimetric sensing. We examine the potential of this metasurface for reflective strain sensing, where the periodicity of the meta-atoms could ultimately be modified by a potential flexion, and for localized surface plasmon resonance refractive index sensing. This study evaluates the potential of streamlined meta-atom design combined with low-cost metallization for inexpensive sensor readout based on human optical perception.

Metasurface Color Filters Using Aluminum and Lithium Niobate Configurations

Two designs of metasurface color filters (MCFs) using aluminum and lithium niobate (LN) configurations are proposed and numerically studied. They are denoted as tunable aluminum metasurface (TAM) and tunable LN metasurface (TLNM), respectively. The configurations of MCFs are composed of suspended metasurfaces above aluminum mirror layers to form a Fabry-Perot (F-P) resonator. The resonances of TAM and TLNM are red-shifted with tuning ranges of 100 nm and 111 nm, respectively, by changing the gap between the bottom mirror layer and top metasurface. Furthermore, the proposed devices exhibit perfect absorption with ultra-narrow bandwidth spanning the whole visible spectral range by composing the corresponding geometrical parameters. To increase the flexibility and applicability of proposed devices, TAM exhibits high sensitivity of 481.5 nm/RIU and TLNM exhibits high figure-of-merit (FOM) of 97.5 when the devices are exposed in surrounding environment with different refraction indexes. The adoption of LN-based metasurface can enhance FWHM and FOM values as 10-fold and 7-fold compared to those of Al-based metasurface, which greatly improves the optical performance and exhibits great potential in sensing applications. These proposed designs provide an effective approach for tunable high-efficiency color filters and sensors by using LN-based metamaterial.