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‘Invisible glass’ created at BNL has broad uses, researchers say

Charles Black, left, holds conventional glass on Jan.

Charles Black, left, holds conventional glass on Jan. 2, 2018 as Andreas Liapis gazes through "invisible glass" developed at Brookhaven National Laboratory. Credit: Newsday / Thomas A. Ferrara

Scientists at Brookhaven National Laboratory have created “invisible glass” that eliminates nearly all glare and potentially could find uses in eyeglasses, smartphones, solar panels and auto windshields.

The glass is virtually invisible because it transmits nearly 100 percent of light across a broad spectrum, including wavelengths visible to humans, said Charles Black, lead researcher and director of the laboratory’s Center for Functional Nanomaterials.

Black said the assembly process, which creates a “nanotexture” of tiny cones just billionths of a meter tall on the glass, potentially could be adapted for large-scale production. Manufacturers of glass and eyeglasses already have extended feelers to learn about the technology, he said.

Black was the lead author of an Oct. 30 article on the breakthrough in the journal Applied Physics Letters. Brookhaven Science Associates, the company founded by Stony Brook University and Columbus, Ohio-based Battelle, which runs the laboratory for the U.S. Department of Energy, has applied for a patent on the process.

The article points out that glass with the nanotexture can improve the performance of solar cells by letting them harvest the light typically lost through reflection.

Andreas Liapis, a co-author on the BNL research team and now a research fellow at Massachusetts General Hospital’s Wellman Center for Photomedicine, said that a standard piece of glass reflects about 8 percent of light and transmits the other 92 percent.

By contrast, he said, glass etched with the cones transmits 99.7 percent of light.

Glass reflections arise when light passes from one medium to another. Black said the tiny cones “soften” the transition of light as it travels from air to glass.

The cones are able to usher light into the glass because they are smaller than the wavelength of light, which is about 400 to 700 nanometers.

Because the cones are smaller than a lightwave, Black said, “the light won’t see the individual structure” of the cones and bounce back as a reflection.

The transition takes place at nanoscale dimensions. For perspective, a nanometer is one billionth of a meter and a grain of sand is about 250,000 nanometers in diameter. The cones are 250 nanometers tall and 50 nanometers wide, so they’re more than 1,000 times smaller than a grain of sand.

The researchers used equipment to etch the glass that’s similar to that used in producing computer chips.

“We’ve married the world of nanoscience to create these small features from machines used to make technology around us, in particular semiconductors,” Black said.

They use a template, or stencil, to define where the cones will be on the glass and then stream a very hot gas, known as plasma, to etch the pattern.

The applications for the technology are wide, Black said, in part because glass itself comes in so many forms.

“If you throw other things into glass, you can make it more bendable or heat-tolerant,” he said.

Black and other researchers have turned for inspiration to nature, in particular the structure of moth eyes, which are covered with nanoscale posts.

“The moth is a nighttime animal that needs to collect as much light as possible in low-light conditions,” Black said. In addition, the non-reflective eyes shield nocturnal moths from predators that could be alerted by a reflection.

Black said that his group is not the first to create mothlike structures to cut glare. Others have created coatings to apply to glass.

But, Black said, the nanotextures “perform more than twice as well” as broadband anti-reflection coatings in reducing glare and more than three times as well when the light hits the glass at an angle.

Further, the technique could be used to produce the glass economically outside the laboratory, he said.

“The next step for us is to find the right partners.”

A third co-author was Atikur Rahman, a former researcher at the laboratory and now an assistant professor in the department of physics at the Indian Institute of Science Education and Research in Pune, India.

Fast facts

  • Standard glass reflects 8 percent of light and transmits the other 92 percent. “Invisible glass” developed at Brookhaven National Laboratory transmits 99.7 percent of light.
  • To make the glass non-reflective, it is etched with tiny cones 1,000 times smaller than a grain of sand.
  • The glass could be used in eyeglasses, smartphones, solar panels and auto windshields.

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