Graphene is the strongest material in the world, even when it has notable defects, new research has found. Even when stitched together from numerous small crystalline grains, rather than being created directly in its perfect crystalline form, the material possesses its trademark and remarkable strength. This new research contradicts previous theoretical simulations which predicted that such defect-containing graphene would be much weaker than graphene in a perfect lattice.
It’s been said that graphene is so strong that “it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” The impressive strength of the material, as well as its many other remarkable qualities — the ability to convert a single photon of light into multiple electrons, the absorption of a very large spectrum of light, unique optical properties, etc — make it a very appealing and potentially revolutionary material.
Graphene is — essentially — just a single atomic layer of carbon that is structured as a honeycomb lattice. “Our first Science paper, in 2008, studied the strength graphene can achieve if it has no defects — its intrinsic strength,” says James Hone, professor of mechanical engineering at Columbia Engineering, who led the study with Jeffrey Kysar, professor of mechanical engineering. “But defect-free, pristine graphene exists only in very small areas. Large-area sheets required for applications must contain many small grains connected at grain boundaries, and it was unclear how strong those grain boundaries were. This, our second Science paper, reports on the strength of large-area graphene films grown using chemical vapor deposition (CVD), and we’re excited to say that graphene is back and stronger than ever.”
The new research corrects the mistaken belief that defects present in graphene are the cause of the extremely low strength seen in some previous studies — the lowered strength is actually the result of the methods used for post-processing CVD-grown graphene. The Columbia Engineering research team has remedied this by developing a new process which prevents damage from being done to the graphene during transfer.
“We substituted a different etchant and were able to create test samples without harming the graphene,” states the paper’s lead author, Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab. “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.”
The primary way that graphene is currently manufactured is via chemical vapor deposition (CVD). Sheets of graphene as large as television screens can be grown this way. And the method has the advantage of being much-more economical than alternatives.
“But CVD graphene is ‘stitched’ together from many small crystalline grains — like a quilt — at grain boundaries that contain defects in the atomic structure,” Kysar explains. “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.”
So the researchers set out to find what was making CVD graphene weaker than the graphene made with other manufacturing methods. What they found was that a specific chemical used in the process was damaging the graphene, diminishing its strength.
“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,” says Hone. “This strength will be invaluable as scientists continue to develop new flexible electronics and ultrastrong composite materials.”
Possible uses include: next-generation solar cells, ultra-flexible electronics, television screens that roll up like posters, extremely strong composite materials that could eclipse the strength of carbon fiber, and possibly even the creation of a space elevator.
The new research was recently published in the journal Science.