The performance of all-dielectric metasurfaces strongly depends on the high refractive index contrast between the nanostructures and the surrounding medium. As a consequence, changing the working environment of a well-designed metasurface, which usually occurs in biological applications, will degrade the performance severely such that re-design becomes necessary. Geromel et al. present a method to solve this problem by covering the high-index nanostructures with a low-index porous SiO2 film. With this buffer layer separating the localized modes from the environment, the metasurface retains its functionality at high efficiency in different dielectric environments. Furthermore, the soaking problem of the porous coating in liquids is solved by adding another transparent waterproofing layer, for example a thick PMMA film.
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