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Camera Flash

Wednesday, August 12, 2009 | Northwestern University


Camera Flash

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A Northwestern Universityprofessor and his students have found a new way of turning graphiteoxide -- a low-cost insulator made by oxidizing graphite powder --into graphene, a hotly studied material that conducts electricity.Scientists believe graphene could be used to produce low-costcarbon-based transparent and flexibleelectronics.

Previous processesto reduce graphite oxide relied on toxic chemicals orhigh-temperature treatment. The idea for a simple new process camein a burst of inspiration: Can a camera flash instantly heat up thegraphite oxide and turn it into graphene?

The process,invented by Jiaxing Huang, assistant professor of materials scienceand engineering at Northwestern's McCormick School of Engineeringand Applied Science, and his graduate student Laura J. Cote andpostdoctoral fellow Rodolfo Cruz-Silva, was published in the Aug.12 issue of the Journal of the American ChemicalSociety.

Materialsscientists previously have used high-temperature heating orchemical reduction to produce graphene from graphite oxide. Butthese techniques could be problematic when graphite oxide is mixedwith something else, such as a polymer, because the polymercomponent may not survive the high-temperature treatment or couldblock the reducing chemical from reacting with graphiteoxide.

In Huang's flashreduction process, researchers simply hold a consumer camera flashover the graphite oxide and, a flash later, the material is now apiece of fluffy graphene.

"The light pulseoffers very efficient heating through the photothermal process,which is rapid, energy efficient and chemical-free," hesays.

When using a lightpulse, photothermal heating not only reduces the graphite oxide, italso fuses the insulating polymer with the graphene sheets,resulting in a welded conducting composite.

Using patternsprinted on a simple overhead transparency film as a photo-mask,flash reduction creates patterned graphene films. This processcreates electronically conducting patterns on the insulatinggraphite oxide film -- essentially a flexiblecircuit.

The research grouphopes to next create smaller circuits on a single graphite-oxidesheet at the single-atom layer level. (The current process has beenperformed only on thicker films.)

"If we can make anano circuit on a single piece of graphite oxide," Huang says, "itwill hold great promise for patterning electronicdevices."