The Morpho butterfly is known for its bright blue wings, but it has no pigmentation. The photonic crystals on its wings reflect only blue wavelengths, allowing other light to pass through, resulting in its blue appearance. The chameleon changes its skin color to match its surroundings in the same way. The path has been opened to preserve masterpieces or cultural assets in graphics that do not change color like a butterfly.
Kim Shin-hyeon, a professor in the Department of Bio-chemical Engineering at the Korea Advanced Institute of Science and Technology (KAIST), and his research team announced on the 26th that they had succeeded in creating high-resolution color graphics that do not change color over time by mimicking the structural coloration principles of butterflies and chameleons. Using this method, they implemented the Five Peaks of Sun and Moon painting from the Joseon Dynasty to the size of a thumbnail. The research results were published in the international journal Advanced Materials on the 5th.
Pigments reflect specific wavelengths of light to produce their color. The remaining wavelengths are absorbed, generating heat. Over time, chemical reactions occur in the pigments, causing color changes. Structural coloration, on the other hand, changes color based on the nanoscale structure rather than being a material, allowing one material to produce various colors without discoloration or fading.
The challenge lies in implementing the regular nanostructures needed for structural coloration. To display the desired color, intricate patterns must be created, which has proven difficult. Professor Kim Shin-hyeon's research team resolved this issue by creating hemispherical microstructures using semiconductor processes.
When light enters the hemispherical microstructures resembling rice bowls, it is reflected along the curved surface. If the diameter of the hemisphere is around 10 micrometers (1 micrometer equals one-millionth of a meter), light following different paths interferes in the visible light spectrum, producing structural coloration.
The research team also found a method to adjust the structural coloration based on the size of the hemispheres. By arranging hemispheres of different sizes like mixing paint on a palette, they can infinitely increase the range of colors that can be displayed. The research team created the hemispherical microstructures using positive photosensitive polymers used in semiconductor processes. When exposed to ultraviolet light, the polymer easily dissolves in the developing solution.
The ultra-precise color graphic technology developed by the research team changes color depending on the angle of incidence of light or viewing angle. Additionally, it displays color only in one direction of the pattern while the opposite side remains transparent. The structural color graphics possess high resolution comparable to the latest light-emitting diode (LED) displays, capable of containing intricate color graphics the size of a thumbnail.
In fact, the research team recreated the Five Peaks of Sun and Moon painting from the Joseon Dynasty behind the throne where the king sat, using 200,000 micro hemispheres at the size of a thumbnail. Because it was created without pigments, it can be preserved permanently without discoloration or fading. They also accurately reproduced masterpieces such as "Impression, Sunrise" and "Girl with a Pearl Earring."
Professor Kim Shin-hyeon noted, "The newly developed color graphic implementation technology without pigments could serve as an innovative method for expressing new forms of art by integrating with art in the future, and is expected to be applicable in various fields, including optical devices or sensors, anti-counterfeiting materials, and aesthetic photo cards."
References
Advanced Materials (2025), DOI: https://doi.org/10.1002/adma.202413143