Chuck Bednar for redOrbit.com – Your Universe Online
Drawing inspiration from a pentagonal pattern of tiles found on the streets of Cairo, researchers from the US, China and Japan have developed a new structural variant of carbon that appears to be dynamically, thermally and mechanically stable.
The newly discovered material is known as penta-graphene, and it is a very thin, single-layer sheet of carbon pentagons. Unlike most forms of carbon, which are comprised of hexagonal building blocks occasionally interspersed with pentagons, penta-graphere would be a unique two-dimensional carbon allotrope made up entirely of five-sided polygons.
“The three last important forms of carbon that have been discovered were fullerene, the nanotube and graphene,” said Dr. Puru Jena, distinguished professor in the Department of Physics at the Virginia Commonwealth University College of Humanities and Sciences and senior author of a new paper appearing in the journal Proceedings of the National Academy of Sciences. “Each one of them has unique structure. Penta-graphene will belong in that category.”
It started with a dinner in China
The research that led to the material was launched at VCU and Peking University, and inspired by one professor’s trip to a restaurant in Beijing. While dining with her husband, Dr. Qian Wang, a professor at Peking University and an adjunct professor at VCU, noticed a piece of artwork that depicted pentagon tiles from the streets of Cairo hanging on the wall.
“I told my husband, “Come, see! This is a pattern composed only of pentagons,’” Dr. Wang explained. “I took a picture and sent it to one of my students, and said, ‘I think we can make this. It might be stable. But you must check it carefully.’ He did, and it turned out that this structure is so beautiful yet also very simple.”
By using computer simulations to model the synthesis of penta-graphene, the researchers found that the material could potentially outperform graphene in some applications. It would be quite strong, mechanically stable and able to withstanding temperatures of up to 1,000 degrees Kelvin. It is also a semiconductor, while graphene is a conductor of electricity, they noted.
“You know the saying, diamonds are forever? That’s because it takes a lot of energy to convert diamond back into graphite. This will be similar,” Jena said. “When you take graphene and roll it up, you make what is called a carbon nanotube which can be metallic or semiconducting. Penta-graphene, when you roll it up, will also make a nanotube, but it is always semiconducting.”
It also stretches in an unusual way, Wang said: “If you stretch graphene, it will expand along the direction it is stretched, but contract along the perpendicular direction. However, if you stretch penta-graphene, it will expand in both directions.”
Penta-graphene derives its mechanical strength from a rare property, Negative Poisson’s Ratio, which could allow for unique technological applications, the researchers said. The material’s property indicates that it could be used in electronics, biomedicine, nanotechnology and more. First, however, the carbon variant must actually be synthesized.
“Once you make it, it [will be] very stable,” Jena said. “So the question becomes, how do you make it? In this paper, we have some ideas. Right now, the project is theoretical. It’s based on computer modeling, but we believe in this prediction quite strongly. And once you make it, it will open up an entirely new branch of carbon science.”
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