Stabilizing the Plasmonic Response of Titanium Nitride Nanocrystals with a Silicon Oxynitride Shell: Implications for Refractory Optical Materials

We discuss the synthesis and properties of nanoparticles and thin films for refractory plasmonic applications. The approach focuses on titanium nitride (TiN), which overcomes the limitations of more common plasmonic materials like silver and gold with respect to temperature stability. Freestanding TiN-based nanoparticles are produced in two serially connected plasma reactors, where TiN nanocrystals are nucleated in a first plasma stage, then aerodynamically dragged in a second stage, and conformally coated with a silicon nitride layer. An in-depth comparison between bare and coated TiN nanoparticles is presented in terms of the structural, chemical, and optical properties. Coating of the titanium nitride core reduces its oxidation upon exposure to air, drastically improving the plasmonic response. Thin films realized using the core-shell structure show practically no change in reflectivity, even when the thin films are heated to 900 degrees C in an inert atmosphere. This study introduces a simple surface passivation scheme that enhances the functionality of the material, providing further confirmation of the potential of nitride-based plasmonic materials as high-quality refractory optical compounds for a broad range of applications.