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January 29, 2008

Another step closer to large scale graphene electronics

Researchers from University of Wollongong, New South Wales have a new and better way of separating graphene sheets. Their process allows sheets to be kept apart in aqueous solution by electrostatic repulsion alone - without the need for chemical stabilizers.

Graphene sheets have an extremely large surface area and non-bonding interactions can cause the sheets to stack together into graphite. Current ways of producing them involve carefully peeling away individual sheets from graphite - a process that is impractical on a large scale.

One alternative is to use chemicals to break down graphite oxide into graphene - but this has previously required surfactants and polymers to keep the individual sheets apart, preventing the graphene from being easily integrated into materials or devices.


Professor Wallace said that this low-cost approach offers the potential for large-scale production of stable graphene colloids that can be processed using well-established solution-based techniques — such as filtration or spraying — to make conductive films.

Director of the ARC Centre of Excellence for Electromaterials Science (ACES), Professor Gordon Wallace, said results already indicated that the discovery would lead to advances in energy conversion (new transparent electrodes for solar cells) , energy storage (new electrodes for batteries -- especially flexible batteries) and as new electrodes in medical bionics.

“In addition to antistatic coatings, these materials are expected to have applications in flexible transparent electronics, high-performance composites and nanomedicine,” he said.



PhD student Benjamin Mueller holds a solution of graphene oxide solution watched on by fellow research team members Dr Dan Li and Professor Gordon Wallace

'The method proposed in this paper should allow easier production of high quality graphene,' Kostya Novoselov of the University of Manchester's mesoscopic physics group in the UK, told Chemistry World. 'There are many possibilities for this, such as making transparent electrodes for LCD displays. At the moment we can only make small displays with graphene, but using this method we could potentially make full-scale displays.'

The team have filed a patent on their new process and are continuing to study the fundamental properties of graphene and investigating its potential in energy conversion and storage.

Meanwhile, another study published earlier this month reports a new chemical technique to make strips of graphene or 'carbon nanoribbons'. Hongjie Dai and colleagues at Stanford University, US, first loosened layers of graphene from graphite by heating it to 1000ÂșC for a minute in 3 per cent hydrogen in argon gas. The team then broke up the graphene into strips using ultrasound. Nanoribbons made in this way have much 'smoother' edges than those produced by traditional lithographic methods, the researchers say.

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