Sunday, April 18, 2010

Graphene Advances

Mass produced graphene Transistors just got a little closer with this laboratory advance in graphene film fabrication.

"Before we can fully utilize the superior electronic properties of graphene in devices, we must first develop a method of forming uniform single-layer graphene films on nonconducting substrates on a large scale," says Yuegang Zhang, a materials scientist with the Lawrence Berkeley National Laboratory (Berkeley Lab). Current fabrication methods based on mechanical cleavage or ultrahigh vacuum annealing, he says, are ill-suited for commercial-scale production. Graphene films made via solution-based deposition and chemical reduction have suffered from poor or uneven quality.

Zhang and colleagues at Berkeley Lab's Molecular Foundry, a U.S. Department of Energy (DOE) center for nanoscience, have taken a significant step at clearing this major hurdle. They have successfully used direct chemical vapor deposition (CVD) to synthesize single-layer films of graphene on a dielectric substrate. Zhang and his colleagues made their graphene films by catalytically decomposing hydrocarbon precursors over thin films of copper that had been pre-deposited on the dielectric substrate. The copper films subsequently dewetted (separated into puddles or droplets) and were evaporated. The final product was a single-layer graphene film on a bare dielectric.

"This is exciting news for electronic applications because chemical vapor deposition is a technique already widely used in the semiconductor industry," Zhang says.
It is always nice to have a process that just needs to be adjusted. Even nicer is that it is a production process. There are probably 1,000 more steps like that required before your next microprocessor is made of charcoal (with a few enhancements).

Graphene has some exceptional properties.
In a semiconductor there is a quadratic relationship between the energy and momentum of the electrons. But in graphene that relationship is linear. Papers #2 (Geim’s group) and #3 (Philip Kim’s group, Columbia University, New York), published side by side in Nature, report on an important consequence of the linear relationship. They independently discovered that electrons move through the films as if they have no mass. That’s because the energy-momentum relationship means that electron transport is governed by the relativistic Dirac equation.

In semiconductors, electron transport is ruled by the non-relativistic Schrödinger equation. So electrons in graphene behave like relativistic particles and travel at about 106 m s-1. Although that speed is about 300 times slower than the velocity of light, it is much faster than the speed of electrons in conductors. The electrons travel sub-micron distances without scattering, something unheard of in semiconductors. Suddenly, ballistic transistors, in which electrons barrel through the device like a bullet, begin to look feasible.
I think massless electrons could come in quite handy. Provided you could produce them on demand and control them. You know. Power and Control.

Here is a fairly recent book on the subject that may help you get up to speed:


H/T DavidWillard at Talk Polywell

Cross Posted at Classical Values

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