Thermal oxidation of TiN nanocylinder arrays: effects of insulator coatings by atomic layer deposition

Titanium nitride (TiN) is a plasmonic material, which efficiently absorbs the solar spectrum and is useful for light-to-heat conversion. Although TiN nanostructures have been developed for plasmonic applications including heat generators, TiN oxidizes to titanium dioxide (TiO2) at relatively low temperatures, as low as 350 °C in air, which limits the application of TiN. In this study, we protect TiN nanocylinder arrays with conformal coatings of insulator layers fabricated by atomic layer deposition. The coating increases the oxidation temperature of the TiN array in air up to 750 °C through suppression of oxygen diffusion by the insulator layer. We also demonstrate the benefit of the thermal oxidation of TiN as a route for nanofabrication of TiO2, a transparent high-refractive-index material. The TiN nanocylinders are converted to TiO2 nanocylinders without disturbing the periodic arrangement. The resultant TiO2 nanocylinder arrays act as two-dimensional (2D) photonic crystals.