Thermally-switchable spectrally-selective infrared metamaterial absorber/emitter by tuning magnetic polariton with a phase-change VO₂ layer

A metamaterial made of submicron aluminum disks on phase-change vanadium dioxide (VO₂) thin film, which is synthesized by furnace oxidation method, has been fabricated by metal deposition, photolithography, and lift-off processes. By varying over-exposure time during the photolithography process with a stepper, metamaterials with submicron disk diameters down to 0.55 μm were successfully fabricated. Characterized by a Fourier transform infrared microscope, the metamaterial exhibits an absorption peak close to unity at the wavelength around 7 μm at room temperature as a selective absorber, while it is highly reflective once VO₂ becomes metallic after phase transition at higher temperatures. Elucidated by numerical simulation, the spectral absorption peak is attributed to the excitation of magnetic polariton (MP) within the insulating VO₂ film. Once the metamaterial is heated above the transition temperature of VO₂, MP cannot be excited within the metallic VO₂ film, resulting in disappearance or “switch-off” of the absorption peak. The switchable behavior is further explained by an equivalent inductor-capacitor circuit model, which predicted absorption peak wavelengths in excellent agreement with experimentally observed ones of fabricated metamaterials with different disk diameters. This thermally-switchable spectrally-selective metamaterial could facilitate applications in dynamic infrared camouflage and active radiative thermal management.