Transition-Metal Nitrides for High-Temperature Structural Colors

Transition-metal nitrides (TMNs), such as hafnium nitride (HfN), titanium nitride (TiN), and zirconium nitride (ZrN), have emerged as highly promising materials in photonics and plasmonics, drawing significant interest due to their optical properties comparable to those of conventional plasmonic materials like Ag and Ag, with remarkable thermal and chemical stability. While TMNs possess high bulk melting points and impressive resistance to degradation, the impact of scaling down to nanoscale dimensions and exposure to oxidizing environments under high temperatures on their optical properties remains largely underexplored. In this work, we establish a comprehensive experimental framework combining in situ optical characterization and ex situ surface analysis to explore the behavior of TMNs at 600 °C with exposure to oxygen. This oxidation process enables gradual color transitions in TMNs, thereby opening pathways for innovative applications in high-temperature structural color for printing. We further investigate aluminum oxide (Al₂O₃) as a protective coating to effectively prevent oxidation and preserve optical behaviors up to 830 °C, making these coatings suitable for applications in demanding thermal environments. The findings highlight TMNs' potential in next-generation high-temperature photonic devices, balancing optical performance and durability in challenging environments.