Iridescent large-area ZrO2 photonic crystals using butterfly as templates

Intact ZrO2 (with refractive index of 2.12) replica, which is large in size (about 3x4 cm(2)), has been synthesized by using natural butterfly wings as templates. Microstructure characters of original butterfly wing scales are maintained faithfully in this biomorphic ZrO2. All replicas can reflect iridescent visible lights, which can even be observed by naked eyes. Optical microscope investigations indicate that colors reflected by one single scale are different from those done by the overlapped two or even more scales. Colors are not only determined by materials' refractive index, observation angle, and the structure of every single scale, but also by its piled number and modes. With the increase in the number of piled scales, the color is not simply redshifted or blueshifted, which is the most direct and powerful evidence for structural colors.