Structural Color Expression Due to Specular Reflection from Bird Feathers

Abstract

In order to clarify the relationship between the structural color and the nanolevel structure of bird feathers, the cortical thin-film structure, the shape of melanin granules, and their arrangement were observed using transmission electron microscopy. The reflection spectra were calculated based on the electron microscopic image data using Fresnel's equation to simulate a thin-film interference and Bragg's law to simulate a photonic crystal, then were compared with the actual reflection spectra. The simulation spectra calculated using Fresnel's equation were very similar to the reflection spectra from dove and mallard feathers. The reflection spectra from each part of the eye-spot pattern of peacock feathers were very similar to both simulation spectra using Fresnel's and Bragg's equations. In the peacock feathers, the structural color from the cortex and the three-dimensional photonic crystal consisting of the lattice structure of rod-shaped melanin granules were fused to further enhance the selectivity.