If you've ever tried using your phone in bright sunlight only to be greeted with a reflection of your own goofy face, moths might have your back. Inspired by the natural nanostructures that keep the insect's eyes from being a shiny beacon to predators, a research team from the University of Central Florida has developed an antireflective film for phone screens.

Moths' eyes feature a surface covered in a pattern of tiny hexagonal bumps that are each smaller than the wavelength of visible light, meaning that when lights hits the surface it reacts as if the surface has a continuous refractive index gradient with the air. This reduces the reflectivity of the light hitting the surface and keeps the insect better hidden from predators.

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Antireflective films that mimic this ability have been developed over the years to reduce glare on eyeglasses and displays, and make sure solar panels are absorbing as much light as possible. With a clear market for reducing reflections on a smartphone screen, the UCF researchers wanted to adapt the moth-eye structure into a film, which could be a more efficient solution than the battery-draining adaptive brightness feature that many phones currently employ.

The UCF team's thin film is made up of a grid of dimples each about 100 nm wide, resulting in a surface reflection of just 0.23 percent – by comparison, the team says the iPhone's surface reflection is 4.4 percent. Tests showed that the film's contrast ratio is four times better in sunlight, and 10 times better in shade. Besides the key function of reducing glare, the film has some other benefits necessary for a screen that's constantly being poked and prodded.

"Using our flexible anti-reflection film on smartphones and tablets will make the screen bright and sharp, even when viewed outside," says Shin-Tson Wu, lead researcher on the project. "In addition to exhibiting low reflection, our nature-inspired film is also scratch resistant and self-cleaning, which would protect touch screens from dust and fingerprints."

The moth eye-inspired nanostructure of the film, as shown from above (left) and the side (right) (Credit: Shin-Tson Wu, College of Optics and Photonics, University of Central Florida)

As effective as the moth-eye system can be, it's not easy to manufacture films with a detailed, uniform nanostructure on such a large scale. But the UCF researchers say they've managed to create a fabrication technique using self-assembled nanospheres, that can be scaled up to a film the size of a phone screen.

"Although it is known that moth-eye structures can reduce surface reflection, it is relatively difficult to fabricate an antireflection film with this nanostructure that is large enough to use on a mobile phone or tablet," says Guanjan Tan, first author of the study. "Because the structures are so small, a high-resolution and high-precision fabrication technique is necessary."

The next steps for the team include improving the durability and performance of the film.

The research was published in the journal Optica.

Source: The Optical Society

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