Synthesis of micro-nanostructured TiN thin film from a TiO2 Sol Gel

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…). Such metasurfaces sometimes need to be implemented under hard-use conditions, including high temperatures and strong field confinement. Transitionmetal nitrides, like titanium nitride (TiN), are ideal materials to achieve such properties, but TiN’s hardness and chemical inertness make patterning difficult. Here, we demonstrate an innovative direct fabrication process to easily synthesize micro–nanostructured TiN thin film. This new technique consists of combining a direct ultraviolet (UV) −photolithography process with rapid thermal nitridation from a photo-patternable TiO2 sol−gel coating using a low-cost, reproducible process that is compatible with large substrate areas and different shapes. The nanoarchitecture and chemical composition of TiO2 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 TiN-based metasurfaces on various substrates (glasses, plastics, etc.) in complex shapes (non-planar-based surfaces), for demanding photonic applications in the future.