Nanotextured glass becomes 'invisible'

To reduce the annoying glare from the surfaces of cell phones and eyeglasses, manufacturers often coat them with antireflective films. Yet these coatings are limited because they reduce the reflection of light only at certain optimal wavelengths. Now, by directly changing the morphology of glass in a process called nanotexturing, researchers can fabricate glass that cuts down on reflection from light across wide swaths of visible and infrared wavelengths, making the material close to invisible. The new glass could be useful in devices such as laser systems and solar cells, in which light loss causes inefficient performance.

The researchers, led by Charles Black, a materials scientist at Brookhaven National Laboratory, began by creating a patterned polystyrene-b-poly(methyl methacrylate) block copolymer template. When placed over top of glass, the template enables the transfer of its pattern to the material via plasma etching. In this process, which the team had previously developed for silicon, gas runs over the template surface, gouging out trenches in the exposed substrate surface and creating a “forest” of nanocones (Appl. Phys. Lett. 2017, DOI: 10.1063/1.5000965). These nanocones—less than 10 nm in width on average—reduce the reflections from the front and back of materials to less than 0.2% for the whole visible and near-infrared spectrum (450-2,500 nm). Using this method, the team made nanotextured glass substrates up to about 10 cm in diameter. The researchers have not yet tested the materials’ durability, a property that will dictate what applications this approach is suitable for, Black says. In one experiment, the researchers evaluated the efficiency by which a solar cell converted light into electricity with an uncovered device, a device covered with the nanotextured glass, and a device covered with regular glass. They found that the uncovered and nanotextured glass devices were comparable and the regular glass device was about half a percent less efficient. The fabrication process is quite complex, which could make it difficult to scale, says Tolga Aytug, a materials researcher at Oak Ridge National Laboratory. Black acknowledges the limitations of the process but says the team hopes to find commercial partners to help scale up the technology.