Nanostructural cones reduce reflections between layered films.
Credit: Courtesy North Carolina State University Nanostructural cones reduce reflections between layered films.

The multicolored sheen that occurs when light passes through two different media—such as gasoline and water—is technically referred to as thin-film interference. Although this phenomenon has visually compelling qualities, it is undesirable for particular technological applications. In optoelectronic devices or film-based solar cells, for example, thin-film interference indicates inefficiencies caused by internal reflections between different layers of materials.

Seeking a way to reduce this interference, scientists at North Carolina State University looked to moth eyes for inspiration. They noted that the surface structure of the moth eye inherently minimizes reflections in order to deliver a clean optical signal.

"We were inspired by the surface structure of a moth’s eye, which has evolved so that it doesn’t reflect light," said NC State mechanical engineering professor Chih-Hao Chang in a press release. "By mimicking that concept, we’ve developed a nanostructure that significantly minimizes thin-film interference."

Chang and his team developed a method of creating depth in thin-films by fabricating minute conical structures that merge with upper layers of material. When the densely packed nanostructural "columns" located on one film pierce another film above, very little light is reflected between the layers—up to 100 times less than without the cones.

The scientists are currently testing pragmatic uses of their approach, beginning with renewable energy technologies. "Our next steps are to design a solar device that takes advantage of this concept and to determine how we can scale it up for commercial applications," said Chang.

Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.