Broadband light absorber property of metal-coated pillars on cicada wings

The surface of a gold-coated robust cicada wing, with nanometer-sized pillars as bristles, exhibits a broadband light absorber property (wavelengths of 400 - 800 nm), which cannot be observed in the case of a gold-coated brown cicada wing. This difference is owing to the different surface structures of the cicada wings. Scanning electron microscopy reveals that the pillars on the wing surface of the robust cicada are thin (diameter of 0.1 μm) and those of the brown cicada are thick (diameter of 0.5 μm). The spacing between the pillars of the robust cicada is ~0.14 μm, whereas, that of the brown cicada is wide (1 μm). The calculated results, obtained using the finite-difference time-domain (FDTD) method, consider the surface structures, and are consistent with the experimentally obtained spectra. The FDTD calculation also reveals that compared with gold, platinum is a slightly more suitable metal for surface coating, which has a large imaginary permittivity in the visible wavelength range.