Recent Press Releases

Carbon chips and atomic gauze

PR12(07)

Tue, 22 May 2007

Could carbon replace silicon in the electronics of the future? Three years ago, Andre Geim and his co-workers at the University of Manchester showed that graphite, an electrically conducting form of pure carbon, can be split into the separate layers of carbon atoms from which it is made. Single layers, called graphene, provide ultra-thin conducting sheets of material that can be cut up into microcircuits.

At that time, the Manchester group and others reported transistors – the fundamental components of computers and other information-processing circuitry – made from graphene. But they weren’t very good transistors. In silicon chips, transistors generally act as switches that can be turned on and off electronically, which can be built into logic circuits for computing. But the first graphene transistors couldn’t really be turned off – they were rather leaky, always letting some electrical current through. This meant they weren’t up to scratch for making logic circuits and computer chips.

Now Geim’s team has solved that problem, as Leonid Ponomarkenko will explain in a talk at the Condensed Matter and Materials Physics conference organised by the Institute of Physics on 12 April. The Manchester researchers have created transistors from single graphene sheets that pass electrons one by one, in which the current can be switched fully off. These devices work at room temperature (whereas earlier single-electron transistors have often needed cooling to extremely low temperatures), and the researchers say they are “suitable for future computer chips.”

What’s more, they say that these devices can be made much smaller than is currently possible with silicon, allowing more computing power to be packed onto a single ‘carbon chip’. The transistors are made from ribbons of graphene stripped from a sheet, and some of these ribbons are only a few nanometres (millionths of a millimetre) wide. In contrast, commercial silicon-based devices are currently at least about 100 nanometre wide. Although there are efforts to develop methods of making smaller silicon devices, this will ultimately make them leaky. So that a different technology is needed if the current trends in miniaturization of electronics are to persist.

Geim says that in principle it might be possible to make graphene devices at the smallest scale conceivable: from strips no wider than one of the hexagonal rings of six carbon atoms from which the sheets are constructed. This would be less than a nanometre wide. But at the moment, the researchers aren’t able to ‘cut’ the graphene sheets reliably at this scale, and have to rely on chance. That’s a challenge still to be met, but the Manchester team claims that “among all the successors to silicon suggested so far, graphene remains – sadly – the only viable approach.”

In a separate talk at the conference, Kostya Novoselov at Manchester will describe the team’s success in making single graphene sheets – one carbon atom thick – that don’t need to be stuck to other materials in order to remain stable. So far, these sheets have been formed while lying on top of a surface, and it wasn’t clear whether freely hanging sheets would hold together or rip. Geim’s team, in collaboration with researchers in Germany and the Netherlands, has now developed a way to remove the support from a single graphene sheet, by surrounding it with a metal frame and then dissolving away the surface on which it sits. This creates a kind of atomic gauze that the researchers describe as “the thinnest material ever possible”. They think that the sheets, made from carbon rings joined into a chicken-wire array, might be used as sieves for filtering gases, or as almost invisible gauzes for supporting molecules being studied under the microscope.

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