Moth Eyes Inspire Antireflective Coating

Researchers at Tokyo University of Science have developed an antireflective coating inspired by the biostructures in moth eyes. Previous attempts at re-creating the antireflective structure, developed through years of evolution, yielded varying degrees of success; despite recent advances in nanoscience that allows the creation of such technology, barriers of scalability and manufacturing costs remain.

A previous attempt by the researchers created moth-eye molds made from glassy carbon etched with an oxygen ion beam.

“Producing glassy carbon substrates requires the use of powder metallurgy technology, which is difficult to produce molds with a large area,” explained Jun Taniguchi, a professor at 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.”

The Tokyo-based team opted to use an inductively coupled plasma (ICP) system rather than the previously used electron-cyclotron resonance ion source. Though both devices can etch glassy carbon with a concentrated beam of oxygen ions, ICP is able to produce a wider ion beam irradiation range better suited for working on large-area structures.

Scientists have found a way to produce large-area transparent films whose nanostructures are inspired by the moth-eye structure. Courtesy of Pixabay via Ian Lindsay.

After testing with different parameters, the researchers determined that a two-step ICP etching process was best for obtaining the coveted high-quality nanostructured mold. Using the mold and a UV-curable resin, the researchers produced a transparent film with a moth-eye nanostructure.

The film’s reflectance toward visible light was 0.4%, 10× lower than that of a similar film without a nanostructure. Transmittance of light through the film was increased, meaning no trade-off in optical properties occurred as a result of using the film to reduce reflected light.

“We could use these films to improve visibility in flat panel displays, digital signs, and the transparent acrylic plates used everywhere since the start of the COVID-19 pandemic,” said Hiroyuki Sugawara, CTO at Geomatec. “Moreover, antireflective coating could also be an efficient way to improve the performance of solar panels.”

The research was published in Micro and Nano Engineering (www.doi.org/10.1016/j.mne.2020.100077).