Previous processes to reduce graphite oxide relied on toxic chemicals or high-temperature treatment. Instead of that, the Northwestern folks kept it simple, wondering if something like a camera flash could instantly heat up the graphite oxide and turn it into graphene.
The process, invented by Jiaxing Huang, assistant professor of materials science and engineering at Northwestern's McCormick School of Engineering and Applied Science, and his graduate student Laura J. Cote and postdoctoral fellow Rodolfo Cruz-Silva, was published in the Journal of the American Chemical Society.
Materials scientists previously have used high-temperature heating or chemical reduction to produce graphene from graphite oxide. But these techniques could be problematic when graphite oxide is mixed with something else, such as a polymer, because the polymer component may not survive the high-temperature treatment or could block the reducing chemical from reacting with graphite oxide.
In Huang's flash reduction process, researchers simply hold a consumer camera flash over the graphite oxide and, a flash later, the material is now a piece of fluffy graphene.
"The light pulse offers very efficient heating through the photothermal process, which is rapid, energy efficient and chemical-free," he says.
When using a light pulse, photothermal heating not only reduces the graphite oxide, it also fuses the insulating polymer with the graphene sheets, resulting in a welded conducting composite.
Using patterns printed on a simple overhead transparency film as a photo-mask, flash reduction creates patterned graphene films. This process creates electronically conducting patterns on the insulating graphite oxide film -- essentially a flexible circuit.
The research group hopes to next create smaller circuits on a single graphite-oxide sheet at the single-atom layer level. (The current process has been performed only on thicker films.)
"If we can make a nano circuit on a single piece of graphite oxide," Huang says, "it will hold great promise for patterning electronic devices."