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Blue microstructures mimic nature

08 Dec 2003

Diffraction gratings made by US scientists replicate the optical properties of butterfly wings.

Taking inspiration from a butterfly with irridescent wings, US scientists have fabricated microstructures that appear a vivid blue over a wide viewing angle. Once optimized the tiny diffraction gratings may offer a striking alternative to traditional surface finishes such as paints, pigments and dyes. (Optics Letters 28 2342)

“We started examining butterfly wings using electron microscopy and we learned how complex the structures are and difficult to fabricate,” said Mool Gupta, director of the Applied Research Center at Old Dominion University in Virginia, US. “So we came up with a new approach of using micro-gratings with random orientation as a means to achieve color with a wider viewing angle.”

Research at Exeter University, UK, previously demonstrated that the Morpho species of butterfly uses an arrangement of intricate ridges to convert ambient white light into a bright blue color with an outstanding efficiency and viewing angle. Since then the challenge has been to fabricate a man-made structure that mimics the performance.

It seems that Gupta’s team and its coworkers from Alcoa Corporation, the maker of packaging materials, have now done exactly that by using electron beam lithography (EBL).

Their design is based on an array of hexagonal cells in a honeycomb pattern. Each cell contains a diffraction grating with groves running in a different direction. The gratings were made at Cornell University Nanofabrication facility and consist on a layer of PMMA on a silicon substrate. The grooves in each hexagon are 125 nm deep and 220 nm wide.

Experiments show that the multi-grating structure appears blue over a viewing angle spanning 90 to 16 deg. “Our measured diffraction efficiency was about 50% and we are looking to improve it further,” Gupta told optics.org. “As current results are very encouraging we are considering gratings in other parts of the spectrum.”

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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