Advancements in nitridation of TiO₂ layers: Mechanisms, techniques, and applications for TiN thin films

Thin films of titanium nitride (TiN) are extensively utilized across various industrial sectors due to their exceptional mechanical and tribological properties, as well as their high chemical and thermal stability. Additionally, their plasmonic behavior makes them highly promising for optical metasurfaces and innovative plasmonic materials mainly in the visible (around 600–780 nm) and in the near-infrared (NIR) range wavelength according to the permittivity values giving rise to metallic behavior in the considered wavelength range. The layers of TiN can be produced by using reactive deposition technique such as chemical vapor deposition or physical vapor deposition but the process of thermal nitridation by gas is also largely used, in particular to coat wide surfaces. Usually, this process involves heating titanium or titanium alloys at high temperature in a nitrogen atmosphere to form TiN. However, the process of forming TiN by nitriding titanium oxide (TiO₂) is a promising alternative that offers many advantages (the possibility to use sol-gel and a control over the nitrogen incorporation) but is not yet well understood and documented. In this review, the nitriding mechanisms of TiO₂ by ammonolysis and by carbothermal nitriding will be presented and compare. Different nitridation processes will then be described and the electrical, mechanical, optical and plasmonic properties of the nitride TiN films will be compared to the other deposition techniques. The applications and the perspectives of this type of nitridation such as formation of TiN metasurfaces or sustainable process of elaboration of TiN will be presented as well.