Microstructure and optical–infrared properties of vacuum-annealed Ag–TiN–Al2O3 coatings

Abstract

This study investigates the structural and optical–infrared (IR) characteristics of Ag–TiN–Al2O3 multilayer coatings deposited via magnetron sputtering on silicon substrates and subjected to vacuum annealing at 300°C, 400°C, and 500°C. X-ray diffraction analysis confirmed the formation of crystalline Ag and TiN phases, with Al2O3 remaining amorphous. Surface morphology revealed significant grain coarsening at 400°C, correlating with enhanced crystallinity. UV–vis spectra indicated improved visible reflectance at this temperature, while Fourier transform infrared spectroscopy measurements demonstrated a pronounced reduction in IR emissivity, reaching minimum values of 0.020 (3–5 μm) and 0.070 (8–14 μm). These values outperform reported single-layer and bilayer systems such as TiN, Cu–ZrB2, Ag–ZrB2, and Al2O3/ZrB2, confirming the superior IR stealth capability of the multilayer. However, further annealing at 500°C led to oxidation-induced structural degradation, reflected in a marked increase in emissivity. The Al2O3 top layer effectively restricted oxygen diffusion up to 400°C, preserving the multilayer’s integrity. These results confirm the thermal durability and multifunctional potential of the Ag–TiN–Al2O3 system for advanced IR stealth and thermal control applications under moderate thermal loads.