Growth of VO2-ZnS Thin Film Cavity for Adaptive Thermal Emission

Abstract

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. In this study, we used a thin-film coating with the Fabry-Perot (FP) effect to enhance emissivity contrast ({\Delta}{\epsilon}) between VO2 phase-change states. This coating utilizes a novel hybrid material architecture that combines VO2 with a 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 {\Delta}{\epsilon} of 0.63 and grew prototype devices. 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 crystalline growth of monoclinic VO2 on ZnS. Through temperature-dependent FTIR spectroscopy measurements, our fabricated devices demonstrated FP-cavity enhanced adaptive thermal emittance.