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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Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO2 coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO2 films were unstructured and untreated at 500 °C, their effect on formic acid’s degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light.

The phenomenon of resonant reflection from a grating-coupled waveguide mode is conceptually, technologically, and experimentally transposed from a planar corrugated waveguide structure under plane wave excitation to a circularly symmetrical waveguide at the inner wall of a tube under cylindrical wave excitation. The mode coupling element is an azimuthally periodic wall corrugation having an integer number of lines parallel to the tube axis. The grating is defined by diffractive coordinate transform of a radial grating phasemask transverse to the tube axis under axial beam exposure onto a photoresist-coated TiO 2 sol-gel wall-waveguide. The holistic excitation of a waveguide mode is achieved by transforming a broad spectrum, centered axial incident beam into a cylindrical wave by a centered, 90 o apex reflective cone. The expected resonantly reflected cylindrical wave at the mode-coupling wavelength is in turn transformed back into an axial beam by the cone. TE resonant reflection is demonstrated experimentally.

This paper describes a tailored and versatile technology route to achieve micro and nanopatterning of both TiO2 and TiN thin films using a direct photo patternable sol–gel approach combined with a rapid thermal annealing and nitridation process. The approach consists in multi‐scale structuring TiO2 using laser direct writing or mask/colloidal lithography on a wide range of substrates including materials and of diverse geometry. These patterned TiO2 layers can subsequently be converted into a micro‐structured metallic TiN layer using a direct rapid thermal nitridation process that results in metallic thin films (TiN). This work demonstrates the versatility of this complete chain of soft chemistry based new process for patterning TiO2 and TiN thin films thereby avoiding expensive processes such as etching and lift‐off, while preserving their diffractive properties and high thermal stability, that is, up to 1000 °C under vacuum. The process is compatible with different kinds of substrates of different shapes and sizes. These results pave the way for developing a cost‐effective and time‐saving approach to different cutting‐edge applications such as metasurfaces, sensors, and applications in the luxury and decoration sector.