Hybrid oxide-chalcogenide thin film cavity for passive thermal adaptive radiation

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. Vanadium dioxide (VO₂) is a commonly used dynamic response material that can transition from a low emissivity (insulating) state to a high emissivity (radiating) state near room temperature. In this study, we used a thin-film coating with the Fabry-Perot (FP) effect to enhance emissivity contrast (Δε) between the VO₂ phase-change states. This coating utilizes a novel hybrid material architecture that combines VO₂ with the mid- and long-wave infrared transparent chalcogenide, zinc sulfide (ZnS) as a cavity spacer layer. We simulated the design parameter space to obtain a theoretical maximum Δε of 0.63 and grew a prototype device. Using x-ray diffraction, Raman spectroscopy, and Fourier Transform Infrared (FTIR) Spectroscopy, we determined that an intermediate buffer layer of TiO₂ is necessary to execute the polycrystalline growth of VO₂ on ZnS. We optically characterized the pulsed laser deposition grown VO₂ and ZnS using IR-spectroscopic ellipsometry. Through measuring the temperature-dependent FTIR spectroscopy, our prototype sample demonstrated FP-cavity enhanced adaptive thermal emittance.