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.