Moth-eye shaped on-demand broadband and switchable perfect absorbers based on vanadium dioxide

Two biomimetic, moth-eye structure, perfect absorbers in the visible and near infrared regions are introduced and investigated. The moth-eye structure is made up of vanadium oxide (VO2), which is a phase change material that changes from an insulator state to a metallic state at around 85 degrees C. The VO2 structure sits on top of a sapphire (Al2O3) dielectric spacer layer, above a gold (Au) back reflector. Two perfect absorbers are designed, one with perfect absorption over an ultra-broadband range between 400 and 1,600nm, for both the insulating and metallic phases, while the second can switch between being a perfect absorber or not in the range 1,000 and 1,600nm. The absorption profiles and electric and magnetic fields are examined and discussed to provide insight into how absorbers function in the four different situations.