Mimicking Domino-Like Photonic Nanostructures on Butterfly Wings

An effective route to the fabrication of butterfly-mimetic structures using a combination of nanoimprint lithography (NIL) and shear patterning was studied. A silicon nitride mold was processed by traditional lithography and etching processes, which produced a high definition of structures on the surface of the mold. The mold was cleaned in a piranha solution at 120°C for 30mm, rinsed with deionized water, dried in a stream of dry nitrogen, and put in a clean oven at 100°C for 1 h. The mold was then exposed to oxygen plasma operated at 200-mTorr oxygen 10-sccm oxygen flow rate. A collimated white light beam was used to shine the structure in different angles to the surface normal. The reflection was observed using a stereo-microscope placed at the normal direction to the sample surface and connected to a CCD camera. SEM observations showed that the synthetic wing structures have multiple layers, depending on the viewing angle, and that they are separated by air spaces with thicknesses of δ50 nm.