Characterization of optical micro- and nano-structures in non-iridescent color of avian feathers by focused ion beam and electron microscopy

Deok-Jin Jeon1,2, Seungmuk Ji1, Eunok Lee3, Yung Kun Kim3, and Jong-Souk Yeo1,2*

1 School of Integrated Technology, Yonsei University, Incheon, 21983, South Korea

2 Yonsei Institute of Convergence Technology, Yonsei University, Incheon, 21983, South Korea

3 Division of Convergence Research, Bureau of Basic Ecological Research, National Institute of Ecology, Seocheon-gun, Choongnam, 33657, South Korea

E-mail: jongsoukyeo@yonsei.ac.kr

Structural coloration in nature has considerable values for bioinspired optical applications due to its bright and dazzling optical properties. The most common structural coloration mechanism of avian feathers is photonic crystal, however, color with photonic crystal is basically iridescent. Here, we study non-iridescent color of avian feathers with a mechanism that is more than a simple photonic crystal effect.

In this research, we characterize optical structures to investigate non-iridescent blue coloration mechanism of avian feathers by sample preparation with focused ion beam (FIB) and scanning electron microscopy (SEM). These characterization techniques allow us to have systematic approaches to develop energy-efficient coloration mechanism from nature based on avian feathers. We focus on two types of avian feathers which are kingfisher (alcedo atthis) and eurasian jay. They have non-iridescent cyan and blue color feathers at barbs. The barbs contain spongy-like keratin nano-structures, melanin rods, keratin cortex, and melanin black layer. They have roles that lead to their unique reflectance spectra. Optical properties of the feathers are characterized by ultraviolet and visible (UV-Vis) spectrophotometer and optical microscopy. Cross-sectional microscopic images of the feathers' optical structures are obtained through focused ion beam sectioning (FIB) and scanning electron microscopy. By close investigation of the feather, underlying design rule for its brilliant color can be proposed to enable the fabrication of such nanostructures for bio-inspired non-iridescent color applications.

This research was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1B04033182) and also supported by Research Program through the National Institute of Ecology (NIE-basic research-2018-18).

Keyword: non-iridescent, optical structures, structural color