Photonic crystal structures of biologic origin: Butterfly Wing Scales

Photonic crystal type nanoarchitectures (built of chitin and air) occurring in the scales of two male butterflies, with dorsal blue and ventral green coloration were investigated by optical microscopy, SEM and TEM. Reflectance data were collected by normal incidence measurements and by integrated reflectance measurements, too. Reflectance peaks with close positions in the blue range of the spectrum were found both for the single crystalline scales and for the most disordered photonic band gap material. Polycrystalline structures with grain size on the micron scale produce matt reflectors, while moderately ordered “pepper-pot” type structures can yield surfaces with shiny aspect. It was found that the cover scales on each sides of the wing are primarily responsible for the observed colors. The character of the observed colors (shiny, or matt) correlates with the habitat of the investigated butterflies.