Graphene Finally Goes Big

Staff Writer

If there's a rock star in the world of materials, it's graphene: single-atom–thick sheets of carbon prized for its off-the-charts ability to conduct electrons and for being all but transparent. Those qualities make graphene a tantalizing alternative for use as a transparent conductor, the sort now found in everything from computer displays and flat panel TVs to ATM touch screens and solar cells. But the material has been tough to manufacture in anything larger than flakes a few centimeters across. Now researchers have managed to create rectangular sheets of graphene 76 centimeters in the diagonal direction and even use them to create a working touch-screen display.

That scientists can make any devices at all from graphene is impressive. The carbon sheets were isolated only in 2004. Since then, researchers have struggled to produce large swaths of the ultrathin membrane. Last year, a group led by University of Texas, Austin, chemist Rodney Ruoff took a key step, growing graphene squares one centimeter on a side atop flexible copper foils.

Now researchers led by Jong-Hyun Ahn and Byung Hee Hong of Sungkyunkwan University in South Korea report online today in Nature Nanotechnology that they have essentially scaled up the approach taken by the Texas team to make graphene sheets large enough for full-screen displays.

The Korean-led researchers first used a technique called chemical vapor deposition to grow graphene atop large sheets of copper foil. They then added a thin adhesive polymer layer atop the graphene and dissolved away the copper backing. Peeling off the adhesive polymer gave them a single graphene sheet. To make their film stronger, they repeated the initial steps, layering four sheets of graphene atop one another. The researchers then chemically treated their graphene sandwich with nitric acid to improve its electrical conductivity.

The film allowed 90% of light to pass through and had an electrical resistance lower than that of the standard transparent conductor made from indium tin oxide (ITO). The team members also revealed that graphene outperformed ITO when they incorporated it into a real touch-screen display. ITO is used in touch screens, such as those used to record signatures when customers make a credit-card purchase. But it's brittle. Ahn and colleagues showed that their graphene-based touch screen could handle twice as much strain as conventional ITO-based devices.

"It's potentially a really important step along the way for massive scale up" of graphene technology, Ruoff says of the new work. But he cautions that beating out ITO won't be easy. Electronics companies have been working for years to replace ITO with transparent conductors made from films of carbon nanotubes. But they've been undone by small defects in the films that create dead pixels in displays, something the eye can readily see. Still, the indium in ITO is extremely expensive, which ought to give companies every incentive to give graphene a shot at replacing it, says Ruoff.

Posted in Chemistry, Physics, Technology