Dielectric nano-imprint lithography-sol-gel nanostructured for high-sensitivity refractive index sensing

This article demonstrates that the combination of all-dielectric metal oxides sol-gel sensitive materials and metasurfaces, prepared by simple sol-gel methods (dip-coating and soft-Nano Imprint Lithography), can lead to nanocomposite systems with high sensitivity for RI variation and VOC concentration in air detection in spectral shift mode: 4500 nm / RIU ; 0.2 nm / ppm, and in direct reflectance mode: FOM* = 17 ; 0.55 10-3 R / ppm. The metasurface is composed of TiO2 high aspect ratio nano pillars array, replicated from a commercial anti-reflective polymer surface, while the sensitive materials embedding the latter are class II hybrid silica microporous materials containing various types of covalently bonded organic functions. These hybrid layers showed relative significant differences in chemical affinity with different VOCs, which can be exploited to eliminate interferences with air moisture and for qualitative analysis of gas mixtures. We also demonstrated that the presence of the TiO2 metasurface is responsible for the signal intensity increase by almost an order of magnitude in simple reflection mode. This improvement compared to simple Fabry-Perot bi-layer is due to the antenna effect, enhancing the interaction of the confined electromagnetic wave with the sensitive medium. This sol-gel nanocomposite system presents many advantages such as high throughput and low-cost elaboration of the elements, high chemical mechanical and thermal stability ensuring a high stability for detection for long period of time.