Biomimetic isotropic nanostructures for structural coloration.

Many species of birds have feathers that are brilliantly colored without the use of pigments. In these cases, light of specifi c wavelengths is selectively scattered from nanostructures with variations in index of refraction on length-scales of the order of visible light. [ 1 ] This phenomenon is called structural color. The most striking examples of structural color in nature are iridescent colors created by scattering from periodic structures. [ 2 , 3 ] The colors produced by these structures change dramatically depending on the angle of observation. Nature also produces structural colors that have very little angle-dependence. These colors are the result of scattering from isotropic structures. [ 4–6 ] In recent years, periodic biological structures have provided inspiration for groups trying to make photonic materials. [ 7 , 8 ]