“Black” Titania Coatings Composed of Sol–Gel Imprinted Mie Resonators Arrays

Optical technologies and devices rely on the controlled manipulation of light propagation through a medium. This is generally governed by the inherent effective refractive index of the material as well as by its structure and dimensionality. Although a precise control over light propagation with sub-wavelength size objects is a crucial issue for a plethora of applications, the widely used fabrication methods remain cumbersome and expensive. Here, a sol–gel dip-coating method combined with nanoimprinting lithography on arbitrary glass and silicon substrates is implemented for the fabrication of TiO2-based dielectric Mie resonators. The technique allows obtaining sub-micrometric pillars featuring unprecedented vertical aspect ratios (>1) with relatively high fidelity and precision. Spectroscopic characterization at visible and near-infrared frequencies demonstrate that the resonant properties of these dielectric pillar arrays allow for a drastic reduction of light transmission (cutting more than 50% on glass) and reduced reflection (reflecting less than 3% on glass and 16% on bulk silicon), accounting for an efficient light trapping. These results provide a guideline for the fabrication of Mie resonators using a fast, versatile, low-cost, low-temperature technique for efficient light manipulation at the nanoscale.