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Graphene Retains Title as World's Strongest Material

Jun 03, 2013 10:49 AM EDT

Graphene, even in an imperfect form, remains the strongest material in the world, according to new research from Columbia University, which found that the single layer of latticed carbon atoms is virtually unbreakable even when stitched together like a quilt.

Graphene is a one-atom-thick carbon layer. Defect-free graphene exists only in very small amounts. A large sheet of graphene must be quilted together from smaller sheets, and until now, scientists had thought that the grain boundaries, or seams, where the graphene was stitched together were structurally weaker than the rest of the graphene film.

"Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications," said Gwan-Hyoung Lee, the lead author of the paper on their findings, which was published in the journal Science.

In 2008, the same team from Columbia published a paper declaring that in its perfect crystalline form, graphene is the strongest material ever measured, so strong that James Hone, a professor of mechanical engineering and lead graphene researchers, said "it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap."

But for all it's strength, a perfect sample is graphene is impractical as it is laborious to create and too small to be of any great use. To create larger samples of graphene, scientists can use a technique called chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. Currently, sheets of graphene as large as a television screen can be grown using CVD.

"But CVD graphene is 'stitched' together from many small crystalline grains-like a quilt-at grain boundaries that contain defects in the atomic structure," said Jeffery Kysar, a professor of mechanical engineering and part of the research team. "These grain boundaries can severely limit the strength of large-area graphene if they break much more easily than the perfect crystal lattice, and so there has been intense interest in understanding how strong they can be."

After testing the strength of the grain boundaries, the researchers found that the material is still about 90 percent as strong as perfect graphene, even at the grain boundary.

"This is an exciting result for the future of graphene, because it provides experimental evidence that the exceptional strength it possesses at the atomic scale can persist all the way up to samples inches or more in size," said Hone in a news release. "This strength will be invaluable as scientists continue to develop new flexible electronics and ultra-strong composite materials."

The potential commercial and industrial uses for graphene are futuristic and include a television screen that can roll up like a map or, the researchers speculate, an elevator into space connecting an object in orbit to Earth with a long cord of ultra-strong graphene.

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