The fact that the near-2D layers lets electrons travel so freely means the sheets could allow a new generation of super-fast microelectronics, they say.

Prototype devices like transistors have already been made from graphene, but its basic properties are still being explored.

Graphene is the name given to a sheet of carbon atoms arranged in a hexagon pattern. Stacks of such sheets make the pencil-core ingredient graphite, but until recently it had been extremely difficult to isolate single layers.

The new research was carried out by scientists at the University of Manchester – where graphene was first isolated in 2004 – and colleagues from Russia, the Netherlands, and the US.

The team calculated that pure graphene should allow electrons to travel more easily than in any other material, including gold, silicon, gallium arsenide, and carbon nanotubes.

Electronic quality

The mobility of charge in a semiconductor is known as its "electronic quality" and governs the speeds the material is able to provide in electronics.

For example, gallium arsenide is used in cellphone transmitters because its higher electronic quality means it can operate at greater frequencies than the silicon used for most other applications.

At room temperature, gallium arsenide has an electronic quality of 8500 cm2/Vs compared with just 1500 cm2/Vs for silicon. But good quality graphene without impurities should reach up to 200,000 cm2/Vs, according to the new research.

In experiments, the team showed that two different factors were slowing down the movement of charge.

The first factor is a "built-in" speed limit that cannot be changed: ripples in the sheets trap vibrations from heat passing through the graphene, which in turn slow down the travelling electrons.

The second source of electron congestion is impurities in the graphene. These could be removed, however, via better manufacturing, meaning the material's electronic quality should reach the proposed record-breaking levels.

Manufacturing problem

"Graphene exhibits the highest electronic quality among all known materials," says Andre Geim of the Manchester University team. "Our work singles it out as the best possible material for electronic applications."

Walt de Heer at Georgia Tech University, US, says that the projected figure agrees with what he had expected, based on the behaviour of similar materials like nanotubes.

But he adds the result highlights the main barrier between graphene and the electronics industry – it is hard to isolate pure layers of graphene in sheets large enough for industrial manufacture. "They need a workable material presented in large wafers like silicon," he says.

The experimental devices used in the new research were made by carefully peeling off layers of graphene from chunks of graphite using sticky tape. That technique, while useful in the lab, is of little use to semiconductor companies.

De Heer and colleagues are working to overcome this practical problem. They can already cover areas with a few layers of graphene by heating silicon carbide wafers up to 1300 ºC – the heat breaks down the material, leaving the graphene behind.

"We are able to 'grow' a canvas of material that has similar if not identical electrical properties," says de Heer.

The new research will appear in a forthcoming edition of the journal Physical Review Letters

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