Optimized Titanium Nitride Epitaxial Film for Refractory Plasmonics and Solar Energy Harvesting
Ragini Mishra, Ching‐Wen Chang, Abhishek Dubey, Zong-Yi Chiao, Ta‐Jen Yen, Ho Wai Howard Lee, Yu‐Jung Lu, Shangjr Gwo
Abstract
Titanium nitride (TiN) is an emerging material for refractory plasmonics owing to its excellent optical properties in the visible and near-infrared regions, high melting temperature, extreme mechanical hardness, and stability against material degradation in tough environments. Recently, TiN plasmonic metasurfaces have been proposed as optical broadband absorbers and narrow-band thermal emitters, which are critical for high-efficiency solar thermophotovoltaics. Here, we demonstrate a single-layer metasurface broadband absorber made from the oxidation-resistant TiN(111) epitaxial film grown on c-plane sapphire by nitrogen-plasma-assisted molecular beam epitaxy (MBE) with ∼90% absorptivity over the visible spectrum. This is accomplished by optimized plasmonic characteristics of the oxygen-free stoichiometric TiN film grown by MBE, in comparison with titanium oxynitride (TiOxNy) films prepared by the conventional reactive sputtering technique. In addition, the superb thermal and chemical stabilities of MBE-grown TiN metasurface are confirmed by vacuum annealing at 850 °C and irradiation under 130 suns in the ambient environment.