Preparation of Ag+TiN/TiN/Al2O3 Multilayer Coatings by Magnetron Sputtering and Their Optical Properties

A novel Ag+TiN/TiN/Al2O3 multilayer coating was developed via magnetron sputtering and investigated for its structural and infrared optical performance with and without vacuum annealing. The multilayer structure comprises a co-sputtered Ag+TiN base layer for enhanced reflectivity and conductivity, an intermediate TiN layer for thermal stability, and a top Al2O3 dielectric capping layer for environmental protection and optical modulation. Post-deposition annealing at 400°C for 1 h in high vacuum significantly improved the crystallinity and grain size, as confirmed by X-ray diffraction and field-emission scanning electron microscopy. Optical characterization revealed a substantial increase in visible reflectance (from ~22 to ~46%) and a marked decrease in infrared emissivity, particularly in the mid-wave (3–5 μm) and long-wave (8–14 μm) IR windows. The average emissivity was reduced from 0.163 to 0.102 (MWIR) and from 0.251 to 0.201 (LWIR) upon annealing. These results demonstrate that the tri-layer Ag+TiN/TiN/Al2O3 architecture, with thermal treatment, effectively suppresses IR emission while maintaining favorable optical properties, offering strong potential for thermal stealth, aerospace, and energy-efficient applications.