A moth-eye bio-inspired approach to planar isotropic diffraction

A regular hexagonally packed biomimetic moth-eye antireflective surface acts as a diffraction grating at short wavelengths of the visible spectrum and shallow angles of incidence. These gratings display strong backscattered iridescence with 6-fold optical symmetry. The optical symmetry of real moth eyes is effectively infinite as nature utilizes large number of uniquely orientated domains. In this work we report on a biomimetic moth-eye surface created via nanosphere lithography with a very large distribution of close-packed tessellated domains and the resulting optical symmetry is compared to that of another widely known highly isotropic diffraction grating, also inspired by nature, the sunflower pattern. A white-light laser reflectometry system is used to measure and compare the diffraction pattern isotropy from both structures. The tessellated close-packed structure diffraction pattern approaches that of infinite optical symmetry even though the underlying pattern only possesses a six-fold symmetry. Hence, the angular isotropy observed for the sunflower pattern is replicated to a large extent via a self-assembly procedure, whilst circumventing the complicated design and manufacturing requirements of the sunflower pattern.