Butterfly Scales Research Articles

Photonic Crystal Structure and Coloration of Wing Scales of Butterflies Exhibiting Selective Wavelength Iridescence.

The coloration of butterflies that exhibit human visible iridescence from violet to green has been elucidated. Highly tilted multilayers of cuticle on the ridges, which were found in the scales of male S. charonda and E. mulciber butterflies, produce a limited-view, selective wavelength iridescence (ultraviolet (UV)~green) as a result of multiple interference between the cuticle-air layers. The iridescence from C. ataxus originates from multilayers in the groove plates between the ridges and ribs. The interference takes place between the top and bottom surfaces of each layer and incoherently between different layers. Consequently, the male with the layers that are ~270 nm thick reflects light of UV~560 nm (green) and the female with the layers that are ~191 nm thick reflects light of UV~400 nm (violet). T. aeacus does not produce the iridescent sheen which T. magellanus does. No iridescent sheen is ascribed to microrib layers, which are perpendicular to the scale plane, so that they cannot reflect any backscattering. The structures of these butterflies would provide us helpful hints to manipulate light in photoelectric devices, such as blue or UV LEDs.

Micro‐ and nanostructures of iridescent wing scales in purple emperor butterflies (Lepidoptera: Apatura ilia and A. iris)

Apatura ilia (Denis and Schiffermüller, 1775) and A. iris (Linnaeus, 1758) are fascinating butterflies found in the Palaearctic ecozone (excepting the north of Africa). The wings of these insects are covered with a great number of two types of scales positioned like roof tiles. Type I scales are on the surface, while type II scales are situated below them. The structural color of the type I scales is recognized only on the dorsal side of both the fore and hind wings of the males of the aforementioned species. Both types of scales are responsible for pigment color of the wings, but iridescence is observed only in the type I scales. The brilliant structural color is due to a multilayer structure. The features of the scales, their dimensions and fine structure were obtained using scanning electron microscopy. Cross sections of the scales were then analyzed by transmission electron microscopy. The scales of the "normal" and clytie forms of A. ilia have a different nanostructure, but are of the same type. A similar type of structure, but with a different morphology, was also noticed in A. iris. The scales of the analyzed species resemble the scales of tropical Morpho butterflies.

Blue butterflies feel the heat

Bio-inspired by the nano-architectures of iridescent Morpho butterfly scales, scientists have demonstrated a highly sensitive infrared detector that can efficiently upconvert mid-infrared radiation to visible iridescence changes.

Towards high-speed imaging of infrared photons with bio-inspired nanoarchitectures

Inspired by thermal expansion and refractive index changes in the nanostructures of iridescent Morpho butterfly scales, scientists demonstrate upconverted mid-wave infrared detection with a temperature sensitivity of 18–62 mK and a heat-sink-free response speed of 35–40 Hz.

The relationship of selective surrounding response and the nanophotonic structures of Morpho butterfly scales

This paper investigates the sensitivity of micro/nano structures in Morpho butterfly scales to surrounding media. The theory of multilayer-thin-film interference is introduced to explain the mechanism of sensitivity. Two-dimensional optical models with three different geometrical designs and similar size were constructed to authenticate the theory. The rigorous coupled-wave analysis (RCWA) technique was employed for theoretical calculation of vector diffraction. By comparing the modeling results from RCWA with the experimental results, we identified the key to sensitivity, multilayer-thin-film interference occurred over a structure composed of alternating films with high and low refractive indexes. Further, we identified the main characteristics of the scales that were relevant to sensitivity. These characteristics should be applied to designing and fabricating artificial nanostructures for highly sensitive and selective bio-inspired chemical sensors.

Multiple scaled disorder in the photonic structure of Morpho rhetenor butterfly

The iridescence of Morpho rhetenor butterfly is known to result from a photonic structure on wing scales, where multilayer interference and grating diffraction occur simultaneously. We characterize the disorder at the photonic structure length scale and at the butterfly scale. We measure the scattering pattern of the wing. Through RCWA and 1st Born approximation models, we link the different disorders to different features in the scattering patterns.

Light trapping structures in wing scales of butterfly Trogonoptera brookiana

The fine optical structures in wing scales of Trogonoptera brookiana, a tropical butterfly exhibiting efficient light trapping effect, were carefully examined and the reflectivity was measured using reflectance spectrometry. The optimized 3D configuration of the coupling structure was determined using SEM and TEM data, and the light trapping mechanism of butterfly scales was studied. It is found that the front and back sides of butterfly wings possess different light trapping structures, but both can significantly increase the optical path and thus result in almost total absorption of all incident light. An optical model was created to check the properties of this light trapping structure. The simulated reflectance spectra are in concordance with the experimental ones. The results reliably confirm that these structures induce efficient light trapping effect. This functional "biomimetic structure" would have a potential value in wide engineering and optical applications.

Refractive index and dispersion of butterfly chitin and bird keratin measured by polarizing interference microscopy

Using Jamin-Lebedeff interference microscopy, we measured the wavelength dependence of the refractive index of butterfly wing scales and bird feathers. The refractive index values of the glass scales of the butterfly Graphium sarpedon are, at wavelengths 400, 500 and 600 nm, 1.572, 1.552 and 1.541, and those of the feather barbules of the white goose Anas anas domestica are 1.569, 1.556 and 1.548, respectively. The dispersion spectra of the chitin in the butterfly scales and the keratin in the bird barbules are well described by the Cauchy equation n(λ) = A + B/λ(2), with A = 1.517 and B = 8.80·10(3) nm(2) for the butterfly chitin and A = 1.532 and B = 5.89·10(3) nm(2) for the bird keratin.

Moth Wing Scales Slightly Increase the Absorbance of Bat Echolocation Calls

Coevolutionary arms races between predators and prey can lead to a diverse range of foraging and defense strategies, such as countermeasures between nocturnal insects and echolocating bats. Here, we show how the fine structure of wing scales may help moths by slightly increasing sound absorbance at frequencies typically used in bat echolocation. Using four widespread species of moths and butterflies, we found that moth scales are composed of honeycomb-like hollows similar to sound-absorbing material, but these were absent from butterfly scales. Micro-reverberation chamber experiments revealed that moth wings were more absorbent at the frequencies emitted by many echolocating bats (40–60 kHz) than butterfly wings. Furthermore, moth wings lost absorbance at these frequencies when scales were removed, which suggests that some moths have evolved stealth tactics to reduce their conspicuousness to echolocating bats. Although the benefits to moths are relatively small in terms of reducing their target strengths, scales may nonetheless confer survival advantages by reducing the detection distances of moths by bats by 5–6%.

Replication of Butterfly Scales Nano-Structure with Two-Photon Polymerization Method and the Optical Effect Analysis

Biologically structural colors have been attracting more and more researcher’s attention and many bionics theoretical achievements of this kind may be used for surface decorating and product anti-counterfeiting. But further application has been restricted for the bottleneck problem in specimen manufacture, because of the complexity and nano-dimention of the biological structure. In this work, based on the optimized structure parameters of butterfly scales which have structural color, the specimen was manufactured using the ‘two-photon polymerization method’. Using a femto-second laser system and the photoreswast SU8 of polymer monosomic material, specimen of bionic structural color were prepared. The sample was 30×30μm. The manufacture parameters included that the laser intensity was 5.5-7mw, the distance of the adjacent points was 100nm, the exposure time was 0.6ms, and the numerical aperture of the objective lens was 1.4. The optical effects of the replication structure had been calculated with 1D photonic ‘crystal band gap’ theory. The results of the calculation showed a great consistency with natural butterfly structural color. This work is a meaningful exploration for replication of butterfly or other bionic specimens.

Morphological Effects on Surface-Enhanced Raman Scattering from Silver Butterfly Wing Scales Synthesized via Photoreduction

Through a simple room-temperature photoreduction process, this letter conformally replicates 3D submicrometer structures of wing scales from two butterfly species into Ag to generate practical surface-enhanced Raman scattering (SERS) substrates. The Ag replicas of butterfly scales with higher structural periodicity are able to detect rhodamine 6G at a low concentration down to 10(-9) M, which is three orders of magnitude lower than the detectable concentration limit of using quasi-periodic Ag butterfly structures. This result presents a way to select suitable scale morphologies from 174,500 species of Lepidopterans to replicate, as consumable SERS substrates with low cost and high reproducibility.

Fine structure of wing scales of butterflies, Euploea mulciber and Troides aeacus

Wing scales of male Euploea mulciber (E. mulciber) and Troides aeacus (T. aeacus) butterflies were investigated from interest in photonic crystal by scanning electron microscopy and optical reflectance measurement. On the basis of the structural observation, the colouration in different areas in their wings was discussed. It was particularly deduced that a violet-green iridescence characteristic of E. mulciber's forewing is caused only in a wavelength range from ∼380 to ∼510nm by multiple interference from a highly tilted, triple-layered cuticle arrangement on the brown scales. It was also found that T. aeacus does not produce a blue-green sheen such as observed by Troides magellanus because its scales have no multiple cuticle layers but microrib layers unable to produce any backscattering diffraction.

Numerical Analysis on the Optical Role of Nano-Randomness on the <I>Morpho</I> Butterfly's Scale

The blue coloration of Morpho butterflies has anomalously low angular dependence despite the production of color with a selected wavelength based on an interference effect. A key to the mechanism of the specific Morpho-color was suggested to be the randomness of its scale. Using finite-difference time-domain (FDTD) analysis, the role of different kinds of randomness in the structure of the Morpho butterfly's scale was investigated, which was impossible by conventional analytical calculations. The results revealed that incoherence in the incident light plays an essential role, which cannot be realized only by structural randomness. On the other hand, the lateral and vertical randomness, and the number of random components were found each to have an independent role to realize the specific Morpho-color preventing the sharp reflective angular dependence. The direction obtained by the numerical simulations to analyze optically complex random structures will serve not only to understand the scientific principles, but also to design the optical properties of artificial materials.

Using hierarchy architecture of Morpho butterfly scales for chemical sensing: Experiment and modeling

In this work, the hierarchical micro/nanostructures of Morpho butterfly scales were employed for chemical sensing purposes. We observed that the color and the brightness of the butterfly wings change obviously when the surrounding medium was altered. With an optical system setup, we quantified the shift of the major reflection peak and the change in peak intensity, which corresponds to the observed change of color and brightness. In order to guiding the engineering design of artificial butterfly scales as a new platform for chemical sensors, we further constructed two-dimensional optical models with three different geometrical designs. Rigorous coupled wave analysis technique was employed to analyze the models. By comparing the modeling results with experiments, we identified the key characteristics of the butterfly scales that were relevant to chemical sensing applications. These characteristics should be implemented and optimized in designing and fabricating the bio-inspired sensors for sensitive and selective detection of closely related chemicals.

Color based discrimination of chitin-air nanocomposites in butterfly scales and their role in conspecific recognition.

The self-assembled photonic nanoarchitectures occurring in the wing scales of the blue colored males of nine Lycaenid butterfly species, living in the same habitat, were investigated by reflectance measurements followed by automated data processing. The spectral signatures of the nine species analyzed using an artificial neural network software show that despite the fact that all possess similar "pepper pot" type structure, the spectral signatures exhibit enough characteristic differences to allow the unambiguous identification of conspecific individuals. By cross-correlating the position of the individuals of each species in the CIE chromaticity diagram with their flying period it was possible to show that relatively similarly looking, closely related species fly in distinct periods. The spectral identification method may prove useful in the investigation of museum exemplars which cannot be harmed. As the self-assembled, quasiordered, "pepper pot" type photonic nanoarchitectures of various colors seem to pose milder constraints on the production process as compared with perfect photonic crystals, such nanoarchitectures may find practical applications in a wide range from the textile industry to environmentally friendly colorants.

THE BUTTERFLY EFFECT

A NEW EXAMINATION of butterflies’ brightly colored wing scales has the photonics community all aflutter. For the first time, researchers have used small-angle X-ray scattering (SAXS) on single butterfly scales to characterize the three-dimensional photonic nanostructures that make butterfly wings so luminous ( Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0909616107). Yale University’s Richard O. Prum and coworkers looked at five different species from two butterfly families and found that the wing scales’ nanostructure is a single network of gyroid photonic crystals made of air and chitin—the same stuff that makes up the exoskeletons of crustaceans and other insects. Other scientists had previously predicted that the scales have a gyroid structure, but they studied the scales with transmission electron microscopy, which tends to shrink samples, altering their nanostructures. Prum’s team turned to SAXS, a technique that’s only recently been used to study natural photonics materials. “To resolve structures...

“From Butterfly to Wind Turbine”

The lift force and vibration performance of a wind turbine blade with a ‘butterfly skin’ (metallic version of the butterfly scale) were experimentally investigated. Attention was initially directed to this problem by observation of the complex microstructure of the butterfly scale as well as other studies indicating a higher lift on butterfly wings, covered with scales. Results indicated that the ‘butterfly skin’ of an oscillating blade (the airfoil was NACA-230) increased the lift force by a factor of 1.15, and reduced both the damping coefficients by a factor of 1.37, and the frequency by a factor of 1.1. The modification of the aerodynamic effects on the turbine blade was due to an increase of the virtual air mass, which influenced the ‘butterfly skin’. The air cavity of the skin increased the virtual air mass by a factor of 1.14. The interaction mechanism of a ‘butterfly skin’ with a flow is also described.

Investigation of structural colors inMorphobutterflies using the nonstandard-finite-difference time-domain method: Effects of alternately stacked shelves and ridge density

We use the nonstandard-finite-difference time-domain (NS-FDTD) method to investigate the interaction of light with the complicated microstructures in the Morpho butterfly scales, which produce the well-known brilliant blue coloring. The NS-FDTD algorithm is particularly suitable to analyze such complex structures because the calculation can be performed in a short time with high accuracy on a relatively coarse numerical grid. We analyze (1) the microstructure obtained directly by binarizing an electron microgram of the cross section of a scale, (2) the reflection and diffraction properties of three model structures--flat, alternating, and tree-shaped alternating multilayers, and (3) an array of alternating multilayers with random noise superposed on the height of the structures. We found that the actual microstructure well reproduced the reflection spectrum in a blue region by integrating the reflection intensities over all the reflection angles. Under normal incidence, the flat multilayer mainly stresses on multilayer interference except for shorter wavelengths, while alternating multilayer rather enhances the effect of diffraction grating due to longitudinally repeating structure by strongly suppressing the reflection toward the normal direction. In the array of alternating multilayers, the reflection into larger angles is considerably suppressed and the spectral shape becomes different from that expected for a single alternating multilayer. This suppression mainly comes from the scattering of reflected light by adjacent structures, which is particularly prominent for the TM mode. Thus a clear difference between the TE and TM modes is observed with respect to the origin of spectral shape, though the obtained spectra are similar to each other. Finally, the polarization dependence of the reflection and the importance of the alternating multilayer are discussed.

Order-disorder effects in structure and color relation of photonic-crystal-type nanostructures in butterfly wing scales

In order to study local and global order in butterfly wing scales possessing structural colors, we have developed a direct space algorithm, based on averaging the local environment of the repetitive units building up the structure. The method provides the statistical distribution of the local environments, including the histogram of the nearest-neighbor distance and the number of nearest neighbors. We have analyzed how the different kinds of randomness present in the direct space structure influence the reciprocal space structure. It was found that the Fourier method is useful in the case of a structure randomly deviating from an ordered lattice. The direct space averaging method remains applicable even for structures lacking long-range order. Based on the first Born approximation, a link is established between the reciprocal space image and the optical reflectance spectrum. Results calculated within this framework agree well with measured reflectance spectra because of the small width and moderate refractive index contrast of butterfly scales. By the analysis of the wing scales of Cyanophrys remus and Albulina metallica butterflies, we tested the methods for structures having long-range order, medium-range order, and short-range order.

Structural color of Morpho butterflies

Structural color is caused by wavelength-selective scattering of light by microscopic features, such as those on the scales of some insects. The brilliant blue displayed by some male Morpho butterflies is a classic example of this phenomenon. In this paper, experiments used to distinguish structural color from color due to pigmentation are reviewed. A simple electromagnetic model is developed for the structural scattering from Morpho butterfly scales, and the blue color and iridescence normally seen for these butterflies are predicted by this model. The analysis is based on topics usually discussed in courses on electromagnetism and optics and can be used as an example to supplement classroom discussions of these topics.