Abstract
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 °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 1,600 nm, 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 1,600 nm. The absorption profiles and electric and magnetic fields are examined and discussed to provide insight into how absorbers function in the four different situations.
Highlights
Two biomimetic, moth-eye structure, perfect absorbers in the visible and near infrared regions are introduced and investigated
The periodicity of the hexagonal unit cell is defined as P, while the height of the moth-eye structure is given as h and the thickness of the dielectric spacer layer is tspacer
The first, a perfect absorber in both insulating and metallic states from 400 nm to 1,600 nm, is very robust to the incident angle for both TE and TM polarisation, with over 95% absorption up to an incident angle of 60 degrees
Summary
Moth-eye structure, perfect absorbers in the visible and near infrared regions are introduced and investigated. The eyes of moths are made up of an array of antireflective structures They contain parabolic nano-hemispheres with dimensions smaller than that of visible light that act as a region of graded refractive index between the ambient medium and the interface. Moths eyes have been studied theoretically and fabricated experimentally to display their antireflective properties, and we previously designed an ultra-broadband perfect absorber based on this shape using a range of different transition metals[12]. Phase change materials (PCM) have extremely useful characteristics for active nanophotonics An external stimulus such as heat, light or stress causes a PCM to change phase, from a crystalline to amorphous state, or from a metallic to an insulating state, and vice versa. This allows the phase of VO2 to be controlled by its temperature, without having to apply some form of rapid heating or cooling to change its state
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