Transparent Anti-Reflective Coatings: Inspired from Moth eye

 Moth

The eyes of moths have a biological nanostructure that grants them anti-reflective properties. Though researchers have managed to mimic this structure to produce anti-reflective coatings, current techniques are not easily scalable.

Now, researchers from Japan have devised a strategy to produce large-area moth-eye transparent films that greatly reduce reflectance and improve the transmittance. These films could be used to better the visibility of screens and enhance the performance of solar panels.

Scanning electron microscopy images of an anti-reflective thin film produced using the bio-inspired nanostructured mould. Image credit: Jun Taniguchi, Tokyo University of Science

Moths have evolved to develop eyes that are non-reflective. Their eyes have a periodic nanometric structure that makes the eye surface graded, as opposed to polished. This causes most incident light to bend at the surface and therefore, be transmitted through the eye instead of being reflected off it. This nanoscale arrayed structure is so effective that researchers have tried to mimic it using other materials to create anti-reflective coatings with varying degrees of success.

Though this research team had previously succeeded in creating moth-eye molds made of glassy carbon etched with an oxygen ion beam, this approach was not scalable. “Producing glassy carbon substrates requires the use of powder metallurgy technology, which is difficult to use to produce molds with a large area,” explains Professor Jun Taniguchi from Tokyo University of Science, “To overcome this limitation, we tried using only a thin layer of glassy carbon deposited on top a large regular glass substrate.”

After testing with different ICP parameters, the researchers determined that a two-step ICP etching process was best to obtain a high-quality nanostructured mold. Then, they used this mold to produce a transparent film with a moth-eye nanostructure using a UV-curable resin.

The optical properties of this film were remarkable; its reflectance toward light in the visible range was only 0.4%, ten times lower than that of a similar film without the moth-eye nanostructure. The transmittance of light through the material was also increased, meaning that no trade-off in optical properties occurred as a result of using the film to reduce reflected light.