Nanoarchitecture in the black wings of Troides magellanus: a natural case of absorption enhancement in photonic materials
2011
The birdwings butterfly Troides magellanus possesses interesting properties for light and thermal radiation management.
The black wings of the male exhibit strong (98%) absorption of visible light as well as two strong absorption peaks in the
infrared (3 μm and 6 μm) both due to chitin. These peaks are located in the spectral region where the black body emits at
313K. The study of absorption enhancement in this butterfly could be helpful to design highly absorbent biomimetic
materials. Observations of the wings using a scanning electron microscope (SEM) reveal that the scales covering the
wings are deeply nanostructured. A periodic three-dimensional (3D) model of the scale nanoarchitecture is elaborated
and used for numerical transfer-matrix simulations of the absorption spectrum. The complex refractive index of the wing
material is approximated by a multi-oscillator Lorentz model, leading to a broad absorption in the visible range as well as
two peaks in the infrared. The absorption peak intensities turn out to be dependent on the complexity of the
nanostructures. This result clearly demonstrates a structural effect on the absorption. Finally, a comparison with a planar
layer of identical refractive index and material volume lead us to conclude that the absorption is enhanced by
nanostructures.
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