High temperature oxide multilayers for broadband asymmetric thermal emission

The development of thin-film multilayers that can withstand extreme temperatures, while selectively radiating infrared energy outwards to dissipate heat, has important applications in spacecraft thermal control. In this work, we investigate the conditions for designing and fabricating multilayer films, composed of high-temperature stable complex oxide materials, with differential thermal radiation in the inward and outward directions. We pair strontium ruthenate (SRO), a metallic perovskite with high optical constants, with calcium zirconate (CZO), a transparent dielectric. Using optical constants obtained from experimental measurements of our as-grown films, we investigate the emissive asymmetry in various designs. We show that a simple bilayer, containing an absorbing layer with an antireflective coating, is sufficient to demonstrate non-zero asymmetry. By optimizing multilayer structures of up to 8 layers of alternating materials, we demonstrate asymmetry values as large as 0.66 in calculations. Angular calculations show the preservation of asymmetry over a broad angular range of ∼ ± 60 degrees, with minimal effects of the anisotropy of CZO. Our findings indicate that SRO-CZO multilayer films could offer a lightweight and effective solution for directing thermal emission outwards in extreme aerospace environments. This work advances the development of tailored thermal coatings for next-generation space applications.