X-ray snapshot of butterfly wings reveals underlying physics of color

Morpho butterfly
Morpho didius – Museum specimen. Credit: Wikipedia

A team of physicists that visualized the internal nanostructure of an intact butterfly wing has discovered two physical attributes that make those structures so bright and colorful.

"Over millions of years, have evolved sophisticated cellular mechanisms to grow brightly colored structures, normally for the purpose of camouflage as well as mating," says Oleg Shpyrko, an associate professor of physics at UC San Diego, who headed the research effort. "It's been known for a century that the wings of these beautiful creatures contain what are called , which can reflect light of only a particular color."

But exactly how these complex optical structures are assembled in a way that make them so bright and colorful remained a mystery.In an effort to answer that question, Shpyrko and Andrej Singer, a postdoctoral researcher in his laboratory, went to the Advanced Photon Source at the Argonne National Laboratory in Illinois, which produces coherent x-rays very much like an optical laser

By combining these laser-like x-rays with an advanced imaging technique called "ptychography," the UC San Diego physicists, in collaboration with physicists at Yale University and the Argonne National Laboratory, developed a new microscopy method to visualize the internal nanostructure of the tiny "scales" that make up the butterfly wing without the need to cut them apart.

The researchers report in the current issue of the journal Science Advances that their examination of the scales of the Emperor of India butterfly, Teinopalpus imperialis, revealed that these tiny wing structures consist of "highly oriented" photonic crystals.

"This explains why the scales appear to have a single color," says Singer, the first author of the paper. "We also found through careful study of the high-resolution micrographs tiny crystal irregularities that may enhance light-scattering properties, making the butterfly wings appear brighter."

X-rays reveal the photonic crystals in butterfly wings that create color
When you look very close up at a butterfly wing, you can see this patchwork map of lattices with slightly different orientations (colors added to illustrate the domains). Scientists think this structure helps create the brilliant "sparkle" of the wings. Credit: Ian McNulty

These crystal dislocations or occur, the researchers say, when an otherwise perfectly periodic crystal lattice slips by one row of atoms. "Defects may have a negative connotation, but they are actually very useful in improving materials," explains Singer. "For example, blacksmiths have learned over centuries how to purposefully induce defects into metals to make them stronger. 'Defect engineering' is also a focus for many research teams and companies working in the semiconductor field. In photonic crystals, defects can enhance light-scattering properties through an effect called light localization."

"In the evolution of ," he adds, "it appears nature learned how to engineer these defects on purpose."


Explore further

Two-beam super-resolution lithography used to create 3D photonic 'gyroid' nanostructures

More information: "Domain morphology, boundaries, and topological defects in biophotonic gyroid nanostructures of butterfly wing scales" Science Advances, advances.sciencemag.org/content/2/6/e1600149
Journal information: Science Advances

Citation: X-ray snapshot of butterfly wings reveals underlying physics of color (2016, June 10) retrieved 28 February 2021 from https://phys.org/news/2016-06-x-ray-snapshot-butterfly-wings-reveals.html
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