Roll and reel: A freshly made sheet of graphene is transferred onto a polyester sheet as it passes between hot rollers.
Last year, Rodney Ruoff and his team at the University of Texas in Austin showed that graphene could be grown on copper foil. Carbon vaporized at 1,000 degrees would settle atom-by-atom on the foil, which was a few centimeters across. Byung Hee Hong, a professor at Sungkyunkwan University and corresponding author on the paper, says the use of a flexible base presented a solution to the graphene mass-manufacturing dilemma.
“[This] opened a new route to large-scale production of high-quality graphene films for practical applications,” says Hong. “[Our] dramatic scaling up was enabled by the use of large, flexible copper foils fitting the tubular shape of the furnace.” And the graphene sheets could get even bigger. “A roll-to-roll process usually allows the production of continuous films,” says Hong.
In Hong’s method, a sheet of copper foil is wrapped around a cylinder and placed in a specially designed furnace. Carbon atoms carried on a heated stream of hydrogen and methane meet the copper sheet and settle on it in a single uniform layer. The copper foil exits the furnace pressed between hot rollers, and the graphene is transferred onto a polyester base. Silver electrodes are then printed onto the sheet.
The technique shows some potential to be scaled up for mass production. “They particularly show that they are able to grow the graphene [in a way] that is compatible with manufacturing,” says Strano. “It’s a very economical way to manufacture materials.”
Hong sees application for the method in the production of graphene-based solar cells, touch sensors, and flat-panel displays. But he says products will be a while in coming. “It is too early to say something about mass production and commercialization,” he says. Current manufacturing processes for indium tin oxide use a spreading technology that is different from roll-to-roll printing. “However, the situation will be changed when bigger flexible-electronics markets are formed in the near future,” Hong says.