Golden moth-inspired structures with a synergistic effect of interference, absorption and scattering

Abstract

We describe a new type of photonic material inspired by a Diachrysia chrysitis moth, whose nano-structured wings exhibit a prominent golden color. This is a layered photonic structure with a large refractive index contrast, whose alternating layers are rough at the nanoscale level. Theoretical analysis shows that the scattering and interference interact to enhance the local field within the layers and increase the absorption of the material, particularly in the UV–blue part of the spectrum. Theory is experimentally verified using holographically manufactured Bragg gratings in the dichromated-pullulan (DCP). Alternating air-pullulan layers are produced and held in place by sparsely separated nano-pillars. Air voids are filled with 20–100 nm diameter spherical nanoparticles which act as scatterers. Such materials, with a high refractive index contrast and nano-scale scatterers, are important for achieving large reflectance and a broad spectrum, with scattering as an additional mechanism for spectral control.