Butterfly sparkle characterized for chips

Many tropical butterfly species are iridescent: Their wings flash bright, shimmery hues that arise not from pigments but from the way the wings reflect light. Although the insects use their striking colors to lure mates and confuse predators, their iridescence has also caught the attention of a group of engineers. 

 Researchers at Tufts University in Medford, Mass., are studying the optical properties of butterfly wings to determine how they collect and distribute heat. Ultimately, they hope to apply what they learn from the insects to computer chip manufacturing and the assembly of microelectromechanical systems. Haruna Tada presented the group's latest results last week at a meeting of the Materials Research Society in Boston.

 The Tufts researchers compared the iridescent wings of two butterfly species, the Brazilian Morpho menelaus and the Indonesian Papilio blumei. The wings consist of overlapping scales made of chitin, a carbohydrate also found in crustacean shells and insect exoskeletons. 

 The complex structure of the scales determines their color. Each scale contains thin layers of chitin and air, which reflect light in such a way that one wavelength emerges while the others are canceled out. 

 M. menelaus scales consist of folded stacks of chitin lying side by side to form long, parallel ridges. The wings glitter an intense blue. In the vividly blue-green bands on P. blumei wings, the chitin layers are flat and separated by a raised, gridlike structure. 

 The researchers measured how much light individual wing scales reflect over a range of wavelengths. Although the reflectivity of butterfly wings has been well studied, says Peter Y. Wong, "what we're looking at is what's absorbed."

 As expected, the butterfly scales reflect light most strongly in the range of wavelengths corresponding to their observed colors. The scales reflect very little infrared light and must therefore absorb most of it as heat. 

 Knowledge of butterfly wings might help in understanding the optical and thermal properties of computer chips, which likewise consist of finely structured thin films. Chip manufacture demands reliable control of heating and cooling steps. 

"Hopefully, when we go to model microelectronics processing," Wong adds, "we'll have better insight into what are the important phenomena."