Penta-graphene, a new structural variant of carbon, discovered

February 3, 2015 by Brian Mcneill
The newly discovered material, called penta-graphene, is a single layer of carbon pentagons that resembles the Cairo tiling, and that appears to be dynamically, thermally and mechanically stable. Credit: Virginia Commonwealth University

Researchers at Virginia Commonwealth University and universities in China and Japan have discovered a new structural variant of carbon called "penta-graphene" - a very thin sheet of pure carbon that has a unique structure inspired by a pentagonal pattern of tiles found paving the streets of Cairo.

The newly discovered material, called penta-graphene, is a single layer of pentagons that resembles the Cairo tiling, and that appears to be dynamically, thermally and mechanically stable.

"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," said the paper's senior author, Puru Jena, Ph.D., distinguished professor in the Department of Physics in VCU's College of Humanities and Sciences.

The researchers' paper, "Penta-Graphene: A New Carbon Allotrope," will appear in the journal Proceedings of the National Academy of Sciences, and is based on research that was launched at Peking University and VCU.

Qian Wang, Ph.D., a professor at Peking University and an adjunct professor at VCU, was dining in a restaurant in Beijing with her husband when she noticed artwork on the wall depicting pentagon tiles from the streets of Cairo.

"I told my husband, "Come, see! This is a pattern composed only of pentagons,'" she said. "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."

Most forms of carbon are made of hexagonal building blocks, sometimes interspersed with pentagons. Penta-graphene would be a unique two-dimensional carbon allotrope composed exclusively of pentagons.

Along with Jena and Wang, the paper's authors include Shunhong Zhang, Ph.D candidate, from Peking University; Jian Zhou, Ph.D., a postdoctoral researcher at VCU; Xiaoshuang Chen, Ph.D., from the Chinese Academy of Science in Shanghai; and Yoshiyuki Kawazoe, Ph.D., from Tohoku University in Sendai, Japan.

The researchers simulated the synthesis of penta-graphene using computer modelling. 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.

"You know the saying, diamonds are forever? That's because it takes a lot of energy to convert diamond back into graphite," Jena said. "This will be similar."

Penta-graphene has several interesting and unusual properties, Jena said. For example, penta-graphene is a semiconductor, whereas graphene is a conductor of electricity.

"When you take graphene and roll it up, you make what is called a which can be metallic or semiconducting," Jena said. "Penta-graphene, when you roll it up, will also make a nanotube, but it is always semiconducting."

The way the material stretches is also highly unusual, the researchers said.

"If you stretch graphene, it will expand along the direction it is stretched, but contract along the perpendicular direction." Wang said. "However, if you stretch penta-graphene, it will expand in both directions."

The material's mechanical strength, derived from a rare property known as Negative Poisson's Ratio, may hold especially interesting applications for technology, the researchers said.

Penta-graphene's properties suggest that it may have applications in electronics, biomedicine, nanotechnology and more.

The next step, Jena said, is for scientists to synthesize penta-.

"Once you make it, it [will be] very stable. 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 modelling, but we believe in this prediction quite strongly. And once you make it, it will open up an entirely new branch of carbon science. Two-dimensional carbon made completely of pentagons has never been known."

Explore further: Researchers make magnetic graphene

More information: Proceedings of the National Academy of Sciences, www.pnas.org/content/early/2015/01/27/1416591112

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13 comments

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mytwocts
not rated yet Feb 03, 2015
Great idea but can it rival graphene on mobility ?
El_Nose
not rated yet Feb 03, 2015
@mytwocts

please define mobility
coxbd
not rated yet Feb 03, 2015
VCU physics student here, and this is awesome. Dr. Jena is awesome. I'm excited to see what else can be done with this research.
Wake
1.8 / 5 (5) Feb 03, 2015
How could that "just be discovered" when the carbon atom is built that way? Would you expect carbon atoms in a sheet to take some other form?
saposjoint
4 / 5 (1) Feb 03, 2015
Just off the top, a five-sided carbon ring allotrope suggests bond angles and valence-sharing that carbon doesn't normally exhibit.
antialias_physorg
5 / 5 (4) Feb 04, 2015
Penta-graphene has several interesting and unusual properties, Jena said. For example, penta-graphene is a semiconductor, whereas graphene is a conductor of electricity.


That looks like a match made in heaven: Electronics on a single sheet made of all carbon atoms - only the local topology determining what kind of electrical component it is. Now 'just' add in an in insulating structure of carbon (e.g. diamond structure) and you're good to go.
RWT
3.7 / 5 (3) Feb 04, 2015
How could that "just be discovered" when the carbon atom is built that way? Would you expect carbon atoms in a sheet to take some other form?


What do you mean the carbon atom is built that way? Carbon in nature is most commonly covalently bonded sheets of HEXAGONS that are weakly bonded with other sheets, taking the form of graphite. Diamonds are covalently bound in a tetrahedron mosaic. I would think that a pentagonal form of carbon will be difficult to make because it is not natural, see saposjoint's comment above.
Pooua
4 / 5 (2) Feb 04, 2015
"thin sheet of pure carbon that has a unique structure inspired by a pentagonal pattern of tiles found paving the streets of Cairo."

Who was inspired? Did the researchers see the streets of Cairo and think to themselves, "I wonder if I can make carbon sheets do that"?
PPihkala
not rated yet Feb 04, 2015
This might be hard to manufacture if carbon prefers to assemble into other structures, like graphene.
Osiris1
1 / 5 (2) Feb 05, 2015
Lets see if: 1)..We can make it;
2)..It is really really strong;
3)..We can make really long filaments;
4)..We can make a space elevator tether out of it!
Returners
not rated yet Feb 07, 2015
How could that "just be discovered" when the carbon atom is built that way? Would you expect carbon atoms in a sheet to take some other form?


Some of the carbon-carbon bonds are single bonds and some of them are double bonds.

When you see intersections of lines that are 4 lines intersecting, then that atom has 4 single bonds. When you see intersections that are three atoms, then that atom has 2 single bonds and one double bond.
RealScience
not rated yet Feb 09, 2015
@mytwocts

please define mobility


Electron mobility and hole (missing electron) mobility are key properties in electronics.

While the theoretical limit of mobility in graphene is roughly two orders of magnitude higher than in silicon, substrate supporting the graphene currently limits the mobility to about one order of magnitude higher.

mytwocts is wondering whether the penta-graphene has similarly high mobility, as that would be a very useful trait in a semiconductor.
RealScience
not rated yet Feb 09, 2015

Who was inspired? Did the researchers see the streets of Cairo and think to themselves, "I wonder if I can make carbon sheets do that"?


@Pooua - it is in the article:

Qian Wang, Ph.D., a professor at Peking University and an adjunct professor at VCU, was dining in a restaurant in Beijing with her husband when she noticed artwork on the wall depicting pentagon tiles from the streets of Cairo.

"I told my husband, "Come, see! This is a pattern composed only of pentagons,'" she said. "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."


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