Moth-inspired nanostructures take the color out of thin films

May 16, 2013
The nanostructures, inspired by the surface of a moth's eye, limit the amount of light reflected at the thin-film interfaces. Credit: Chih-hao Chang, North Carolina State University

Inspired by the structure of moth eyes, researchers at North Carolina State University have developed nanostructures that limit reflection at the interfaces where two thin films meet, suppressing the "thin-film interference" phenomenon commonly observed in nature. This can potentially improve the efficiency of thin-film solar cells and other optoelectronic devices.

Thin-film interference occurs when a thin film of one substance lies on top of a second substance. For example, thin-film interference is what causes the rainbow sheen we see when there is gasoline in a puddle of water.

Gasoline is transparent, but some light is still reflected off of its surface. Similarly, some of the light that passes through the gasoline is reflected off the underlying surface of the water where the two substances interface, or meet. Because the light reflected off the water has to pass back through the gasoline, it takes a slightly different optical path than the light that was reflected off the surface of the gasoline. The mismatch of these optical path "lengths" is what creates the rainbow sheen – and that phenomenon is thin-film interference.

Thin-film interference is a problem for devices that use multiple layers of thin films, like thin-film solar cells, because it means that some are being reflected – or "lost" – at every film interface. The more thin films a device has, the more interfaces there are, and the more light is lost.

"We were inspired by the of a 's eye, which has evolved so that it doesn't reflect light," says Dr. Chih-Hao Chang, an assistant professor of mechanical and at NC State and co-author of a paper on the research. "By mimicking that concept, we've developed a that significantly minimizes thin-film interference."

This image shows how moth-inspired nanostructures stop thin-film interference by blocking reflected light. The images on the far right show a slide with no thin film. The images in the middle show the slide coated with thin films. Note how thin-film interference results in a variety of colors. The images on the left are of the slide coated with thin films containing the nanostructures. Note the absence of color, and significantly less reflected light. Credit: Chih-Hao Chang, North Carolina State University

The nanostructures are built into thin films that will have a second thin film placed on top of them. The nanostructures are an extension of the thin film beneath them, and resemble a tightly-packed forest of thin cones. These nanostructures are "interfacial," penetrating into whatever thin film is layered on top of them – and limiting the amount of light reflected at that interface. Chang's team found that the an interface featuring the interfacial nanostructures reflects 100 times less light than an interface of without the nanostructures.

"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," Chang says.

Explore further: Lab unveil new nano-sized synthetic scaffolding technique

More information: The paper, "Antireflection Effects at Nanostructured Material Interfaces and the Suppression of Thin-Film Interference," was published online May 15 in the journal Nanotechnology.

Related Stories

New insight into early growth of solid thin films

May 13, 2013

( —The foundation of many modern electronic devices, such as computer chips, are thin films – nanoscale-thickness layers of one material grown on the surface of another. As consumers continue ...

How organic magnets grow in a thin film

Mar 23, 2013

( —Development of organic single molecule magnets opens a great many of applications for magnetic materials and new memory technologies. Organic magnets are lighter, more flexible and less energy intensive in production ...

Peel-and-stick solar cells

Apr 16, 2013

It may be possible soon to charge cell phones, change the tint on windows, or power small toys with peel-and-stick versions of solar cells, thanks to a partnership between Stanford University and the U.S. Department of Energy's ...

Recommended for you

Lab unveil new nano-sized synthetic scaffolding technique

9 minutes ago

Scientists, including University of Oregon chemist Geraldine Richmond, have tapped oil and water to create scaffolds of self-assembling, synthetic proteins called peptoid nanosheets that mimic complex biological ...

Tiny graphene drum could form future quantum memory

Aug 28, 2014

Scientists from TU Delft's Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential ...

Graphene reinvents the future

Aug 27, 2014

For many scientists, the discovery of one-atom-thick sheets of graphene is hugely significant, something with the potential to affect just about every aspect of human activity and endeavour.

User comments : 0