Dec 12, 2008
Graphene goes large scale
Researchers in Australia have developed a chemical-based approach to make gram-scale quantities of graphene. The bottom-up technique involves reacting the common lab reagents ethanol and sodium together and heating up the fused graphene sheets produced, which are then separated by mild ultrasound. Making bulk quantities of graphene in such a way is a step towards real-world applications of the material.
Graphene was first isolated just four years ago by Andre Geim's group at the University of Manchester, who literally peeled off single layers of the material from graphite crystals using sticky tape. Although the researchers produced pristine graphene, the approach cannot be used to produce industrial scales of the material because it is incredibly time consuming and labour intensive and results in yields of just milligrams.
Although other chemical methods to produce graphene exist – for example, by fragmenting oxidised graphite onto sheets of graphene oxide, which is then reduced to graphene with hydrazine – these always produce defective graphene. This is because the chemical processing disrupts the regular hexagonal carbon lattice in the material.
John Stride of the University of New South Wales and colleagues at the Australian Nuclear Science and Technology Organisation have now come up with a new technique to produce graphene from completely non-graphitic precursors – ethanol and sodium. The approach simply involves reacting the two components together under pressure to produce a white powder than turns black when heated. This material is made up of fused carbon sheets that can be broken down into single sheets of carbon using mild sonication.
"Unlike the sticky-tape technique, which is top-down, our approach to graphene synthesis is truly bottom-up in that the precursors are non-graphitic and the carbon lattice is constructed in the reaction," Stride told nanotechweb.org. "It will thus potentially allow us to modify the lattice with hetero-atoms and so further modify the properties of graphene, such as its electrical conductivity."
Graphene is highly conductive and so could be used in high-speed transistors that would have lower losses than conventional silicon devices. Another advantage of graphene that could be exploited is the transparency of a single sheet to light, leading to applications based on transparent electrodes, like displays, touch-sensitive screens and solar cells. Indium tin oxide is currently used for such applications but graphene would make lower-cost units and flexible displays. Graphene could also increase the charge density stored on capacitors thanks to the very high surface of electrodes made of the material, while its low mass makes it suitable for mobile devices.
All such applications will require large-scale production of the material.
The researchers, who have patented their technology, published their work in Nature Nanotechnology. They are now working on making electric storage devices and electrode materials from graphene.
About the author
Belle Dumé is contributing editor at nanotechweb.org