The miniaturization of optical components to control and manipulate light amplitude, phase, and polarization requires micro-to nanostructured metasurfaces that provide resonant light−matter interactions to exploit optical properties in the visible and near-infrared (NIR) range (plasmonic resonances, wavelength filtering, etc.). Such metasurfaces sometimes need to be implemented under hard-use conditions, including high temperatures and strong field confinement. Transition-metal nitrides, like titanium nitride (TiN), are ideal materials to achieve such properties, but TiN's hardness and chemical inertness make patterning difficult. Here, we present an innovative direct fabrication process to easily synthesize a micro−nanostructured TiN thin film. The technological process is based on a direct photo-patternable titanium oxide TiO 2 sol−gel layer converted into TiN with a rapid thermal nitridation process. The nanoarchitecture and chemical composition of TiO 2 and TiN films were investigated by ultraviolet (UV)− visible−infrared (IR) spectroscopy and Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), and high-resolution transmission electron microscopy (HRTEM) coupled with electron energy loss spectroscopy (EELS). We obtained micro−nanotextured crystallized TiN surfaces in a significantly shorter time than with conventional nitridation processes. Due to the sol−gel approach, this work also significantly extends the chances of obtaining TiNbased metasurfaces on various substrates (glasses, plastics, etc.) in complex shapes (non-planar-based surfaces), for demanding photonic applications in the future.

This study reports the optical, electrical and mechanical properties of TiN films prepared by direct rapid thermal nitridation process from a photo-patternable TiO 2 sol-gel layer. The sol-gel approach is compatible to non-planar and large substrates and allows the micro-nanotexturing of crystallized TiN surfaces in a significantly short time, large scale and at a lower cost compared to TiN layer deposition from existing and conventional processes (CVD, PVD, ALD…). In this paper, the optical measurements are carried out by optical spectroscopy in the UV, visible and near-IR region and by ellipsometry. The resistivity and the conductivity are estimated by four-point probe method, while hardness is characterized by nano-indentation experiments. The results indicate that the TiN thin film made by sol-gel method and rapid thermal nitridation are very promising for the manufacturing of optical metasurfaces devices or new plasmonic materials.

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Photocatalysis using semiconductor materials like titania (TiO2) is a key method for environmental purification or solar fuel generation. Nanostructures that maximize incident light absorption are highly desired to enhance depollution rate or solar‐to‐fuel conversion efficiency in limited volumes of catalysts. Here, we report on structural and optical properties of metasurfaces based on a 20 nm thick anatase layer conformally deposited onto a wavelength‐scale two‐dimensional periodic photonic lattice. We investigate the NO degradation using such metasurfaces, and evaluate the impact of the patterning on photocatalytic activities between 340 and 400 nm. In the 380–385 nm range, the mean photochemical efficiency is increased by a factor up to 5.7 compared to flat references, with an overall three‐fold enhancement within the whole spectral range of interest. This approach can be applied to numerous types of systems by varying active materials, leading to substantial improvements in air/water depollution, water splitting or artificial photosynthesis processes.