“Producing glassy carbon substrates requires the use of powder metallurgy technology, which is difficult to use to produce molds with a large area. To overcome this limitation, we tried using only a thin layer of glassy carbon deposited on top a large regular glass substrate.”Jun Taniguchi
A team from Tokyo University of Science and Geomatec in Japan have developed an innovative and scalable approach to producing moth-eye nanostructures and transparent films. They mimicked the non-reflective and periodic nanometric structure of moth eyes to make films that could be used to fabricate molds and films at large scales.
Many advances in anti-reflective coatings have been inspired by the specific biostructures found in moth eyes, which they have evolved to help them remain hidden from potential predators at night. These biostructures work to make the surface of their eyes graded rather than polished so that the majority of incident light is bent at the surface and transmitted through the eye instead of reflecting off it.
Although the team had previously managed to develop moth-eye molds made from glassy carbon etched with an oxygen ion beam, this method was not scalable. However, in this new study published in Micro and Nano Engineering [Yano et al. Microsyst. Nanoeng. (2020) DOI: 10.1016/j.mne.2020.100077], they developed a straightforward approach to making resin films with anti-reflective nanostructures using an inductively coupled plasma (ICP) system rather than the previously used electron-cyclotron resonance ion source.
As team leader Jun Taniguchi said “Producing glassy carbon substrates requires the use of powder metallurgy technology, which is difficult to use to produce molds with a large area. To overcome this limitation, we tried using only a thin layer of glassy carbon deposited on top a large regular glass substrate.” The glassy carbon layer was formed uniformly on the substrate with sputter-coated titanium with an oxygen ion beam using the ICP system
Although both devices are able to etch glassy carbon with a concentrated beam of oxygen ions, ICP technology produces a wider ion beam irradiation range, something more suited for working on large-area structures. On testing a range of ICP parameters, a two-step ICP etching process was shown to be most effective for achieving a high-quality nanostructured mold.
The mold was then used to make a transparent film using a UV-curable resin. The optical properties of this film in terms of its reflectance toward light in the visible range was significant, while the increase in the transmittance of light through the material indicated no loss in optical properties was found in using the film to reduce reflected light.
The films could find applications in enhancing visibility in flat panel displays and digital signs, as well as in anti-reflective coating for improving the performance of solar panels.
Scientists have found a way to produce large area transparent films whose nanostructures are inspired by the moth eye structure (Credit: Ian Lindsay on Pixabay)