Thermally Robust Plasmonic Nanorings from Titanium Nitride.

Plasmonic nanostructures are widely utilized in fields such as chemical sensing, photothermal therapy, and optoelectronics due to their ability to confine and enhance electromagnetic fields at the nanoscale. Among these, nanorings offer unique advantages owing to their hollow-core geometry, which supports multiple plasmonic modes and enables efficient analyte access. However, conventional plasmonic materials such as gold, silver, or copper suffer from poor thermal stability due to either oxidation or morphological degradation, rendering them unsuitable for high temperatures or chemically harsh environments. In this study, we investigate titanium nitride (TiN) as a robust alternative for the fabrication of thermally stable plasmonic nanorings. TiN combines metallic optical behavior in the visible to near-infrared range with excellent thermal, mechanical, and chemical stability, making it particularly suitable for harsh-environment sensing applications. Using Hole-mask Colloidal Lithography (HCL), a scalable and cost-effective bottom-up technique, we successfully fabricate well-defined TiN nanorings over large substrate areas. We further evaluated their structural and spectral resilience through annealing experiments conducted up to 400 °C in air. The results demonstrate that TiN nanorings maintain their morphology and localized surface plasmon resonance (LSPR) characteristics under elevated temperatures, in stark contrast to their noble-metal counterparts. This work establishes a reproducible, scalable route for producing refractory plasmonic nanostructures and highlights the potential of TiN nanorings for robust operation in high-temperature sensing platforms.