While stock market mavens try to find an angle for making a buck on graphene, researchers are just trying to find a way to manufacture the material in a way that could work at industrial scale while maintaining high quality. It’s proving much more difficult than expected.
Now researchers at the University of Texas at Austin have developed a new method by which very large flakes of single-crystal graphene can be produced that exhibit excellent electrical properties. The Austin engineers claim that these graphene crystals are 10 000 times larger than the largest crystals they could produce only four years ago.
The research, which was published in the 8 November edition of the journal Science (“The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper”), found that if the amount of oxygen that the crystals were exposed to was limited at the beginning of their growth, then only the strongest and fittest would survive and the others would never grow. While this meant there were fewer crystals, it also meant that the ones that survived were very large. And with graphene crystals size matters.
“The game we play is that we want nucleation (the growth of tiny ‘crystal seeds’) to occur, but we also want to harness and control how many of these tiny nuclei there are, and which will grow larger,” said Rodney S. Ruoff, professor in the Cockrell School of Engineering, in a press release. “Oxygen at the right surface concentration means only a few nuclei grow, and winners can grow into very large crystals.”
The manufacturing of single-crystal, or monocrystalline, graphene has remained primarily in the realm of the decidedly un-scalable “Scotch tape” method, in which graphene is pulled off in single-layer flakes directly from graphite. The problem is that all the capabilities that everyone is excited about when it comes to graphene, especially for electronic applications, are only achievable with single-crystal graphene.
Sanjay Banerjee, who heads the Cockrell School’s South West Academy of Nanoelectronics at UT Austin, believes that this new manufacturing method is a fundamental breakthrough in the commercialization of graphene.
“By increasing the single-crystal domain sizes, the electronic transport properties will be dramatically improved and lead to new applications in flexible electronics,” says Banerjee in the press release.
The oxygen control method allowed the researchers to increase the crystal size from a millimeter to a centimeter. And, rather than producing hexagonal-shaped crystals, the new method creates crystals with multi-branched edges that resemble a snowflake.
“In the long run it might be possible to achieve meter-length single crystals,” Ruoff said in the release. “This has been possible with other materials, such as silicon and quartz. Even a centimeter crystal size — if the grain boundaries are not too defective — is extremely significant."
“We can start to think of this material’s potential use in airplanes and in other structural applications — if it proves to be exceptionally strong at length scales like parts of an airplane wing, and so on,” he added.
If the method is scalable and the graphene is of the quality that they report, then the challenge will be how to engineer the material into actual products that could use them.
Photo: UT Austin
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.