We present a novel approach to create spinodal-like structures appropriately modulating the instability of the solid state dewetting: many materials, indeed, featuring anomalous suppression of density fluctuations over large length scales are emerging systems known as disordered hyperuniform. The underlying hidden order renders them appealing for several applications, as light management and topologically protected electronic states. These applications require scalable fabrication, which is hard to achieve with available top-down approaches. These spinodal materials are used by a hybrid top-down/bottom-up approach based on sol-gel dip-coating and nano-imprint lithography for the faithful reproduction of the disordered metasurfaces in metal oxides (SiO2 and TiO2).
Fabrication and scaling of disordered hyperuniform (dHU) materials remain hampered by the difficulties in controlling the spontaneous phenomena leading to this novel kind of exotic arrangement of objects. In this work, we demonstrate a hybrid top-down/bottom-up approach based on sol-gel dip-coating and nano-imprint lithography for the faithful reproduction of dHU metasurfaces in metal oxides (MOx). Nano- to micro-structures made of silica and titania can be directly printed over several cm2 on glass and on silicon substrates. Firstly, we describe the polymer mold fabrication starting from a hard master obtained via spontaneous solid-state dewetting. Then we address the effective dHU character of the master and of the replica and the role of the initial thickness of the sol-gel layer on the MOx replicas. Finally, these structures will be optimized towards their exploitation in many potential photonic applications like photonic devices (anti-reflection coatings, quantum emitters).
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.
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