Nanoscale etching renders glass almost invisible
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Researchers at the Centre for Functional Nanomaterials at Brookhaven National Laboratory have demonstrated that it is possible to make glass effectively invisible by altering the geometry of the surface at the nanoscale.
Glare - difficulty seeing due to light - is a frustrating issue with modern display screens. The reflection of light off these transparent surfaces makes it difficult to read a phone in the sunlight or watch a film on a computer screen in darkness.
When light travels from one medium to another and encounters a change in refractive index (which causes light to bend), some is reflected. Light which passes from air to glass experiences a very sudden change in refractive index so much of it is reflected, causing glare.
By etching nanoscale features into a glass surface, the researchers have ensured that approaching light does not encounter such an abrupt change in refractive index. This drastically reduces the amount of light reflected to almost zero.
This was made possible using a method called self-assembly: the spontaneous ability of some materials to form ordered arrangements. The team had previously used this method to produce nanotextures on plastics, glass and silicon in order to give them water-repellent and self-cleaning properties.
In this case, the researchers exploited the self-assembly of a copolymer material – industrial polymers used in many commercial products – as a template to etch the glass surface at the nanoscale.
“This simple technique can be used to nanotexture almost any material with precise control over the size and shape of the nanostructures,” said Professor Atikur Rahman, a physicist at the Indian Institute of Science Education and Research, and co-author of the study.
“The best thing is that you don’t need a separate coating layer to reduce glare and the nanotextured surfaces outperform any coating material available today.”
This approach allowed them to produce a “forest” of sharp-tipped conical nanostructures which almost entirely prevents light from being reflected. This texture is inspired by those found in nature, such as in the anti-reflective eyes of moths.
The nanotextured glass is able to resist reflections across the entire visible spectrum and beyond. As the structure is entirely made from glass, it is far more durable than commercial anti-reflective coatings.
Beyond allowing for the manufacture of glare-free smartphones and other devices, this anti-reflective glass could also vastly improve the efficiency of solar cells by reducing the amount of sunlight lost to reflection to almost zero.
“We’re excited about the possibilities,” said Dr Charles Black, director of the Centre for Functional Nanomaterials and co-author of the study. “Not only is the performance of these nanostructured materials extremely high, but we’re also implementing ideas from nanoscience in a manner that we believe is conducive to large-scale manufacturing.”