An international team of scientists, led by Prof Puru Jena of Virginia Commonwealth University in Richmond, has discovered a new structural variant of carbon called penta-graphene.
Based on extensive analyses and simulations, the team shows that penta-graphene, composed of only carbon pentagons and resembling Cairo pentagonal tiling, is dynamically, thermally, and mechanically stable; the material exhibits negative Poisson’s ratio, a large band gap, and an ultrahigh mechanical strength. Image credit: Virginia Commonwealth University.
“The three last important forms of carbon that have been discovered were fullerene, the nanotube and graphene. Each one of them has unique structure. Penta-graphene will belong in that category,” Prof Jena said.
Penta-graphene is a single layer of carbon pentagons that resembles the Cairo tiling, and that appears to be dynamically, thermally and mechanically stable.
Most forms of carbon are made of hexagonal building blocks, sometimes interspersed with pentagons. The new material is a unique 2D carbon allotrope composed exclusively of pentagons.
Prof Jena and his colleagues simulated the synthesis of penta-graphene using computer modeling.
The results suggest that the material might outperform graphene in certain applications, as it would be mechanically stable, possess very high strength, and be capable of withstanding temperatures of up to 1,000 degrees Kelvin.
Penta-graphene has several interesting and unusual properties. For example, it’s a semiconductor, whereas graphene is a conductor of electricity.
“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,” explained Prof Jena, who is the senior author of a paper published in the Proceedings of the National Academy of Sciences.
The way penta-graphene stretches is also highly unusual.
“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,” said co-author Prof Qian Wang of Peking University in Beijing, China, and Virginia Commonwealth University in Richmond.
The penta-graphene’s mechanical strength, derived from a rare property known as Negative Poisson’s Ratio, may hold especially interesting applications for technology.
Its properties suggest that it may have applications in electronics, biomedicine, nanotechnology and more.
The next step for scientists is to synthesize penta-graphene.
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Shunhong Zhang et al. Penta-graphene: a new carbon allotrope. PNAS, published online February 02, 2015; doi: 10.1073/pnas.1416591112
