April 17, 2008

Graphene nanoelectronics


The Journal Science has a paper "Chaotic Dirac Billiard in Graphene Quantum Dots" which describes the smallest transistor ever made was created using graphene.

Researchers have carved graphene to create the world's smallest transistor, one atom thick and ten atoms wide.

the New Scientist magazine also has coverage

Applying a magnetic field to the smallest dots lets current flow again, making a switchable transistor. The smallest dots that worked as transistors contained as few as five carbon rings – around 10 atoms or 1nm wide.

There are other kinds of prototype transistors in this size range. But they usually need supercooling using liquid gas, says Novoselov. The new graphene devices work at room temperature.

Such prototypes are typically made by building one atom at a time, or wiring up individual molecules. Those approaches are complex and impractical, Novoselov says.

By contrast, the graphene transistors were made in the same way that silicon devices are, by etching them out of larger pieces of material. "That's their big advantage," he says.

The most amazing result for me is that they were able to obtain quantum dots as small as 1 nm," says Antonio Castro Neto of Boston University, US. "This is shocking." "If you try to reduce the dimensions of any other structure, the structure would disintegrate before you reach these dimensions," Neto adds.

"There is no doubt in my mind that these structures can be used for technological applications," he says. "The electronic flexibility and structural stability, fundamental for modern device development, are unmatched in any other material on Earth." But working out how to manufacture graphene devices on a practical scale remains a challenge, he concludes


Graphene quantum dots offer a new approach to quantum nanoelectronics. (article by R. M. Westervelt of Harvard University)

FURTHER READING
Other publications from Westervelt research group at Harvard

Graphene quantum dots may help solve quantum computing problems.

Ensslin, along with fellows at the Solid State Physics Laboratory, Stampfer, Güttinger, Molitor, Graf and Ihn, believe that they can use electron spins from a tunable graphene quantum dot to create qubits, the building blocks of a quantum computer. These graphene-based qubit could rectify some of the problems found with gallium arsenide. As a first step they present a graphene single electron transistor in Applied Physics Letters: “Tunable Coulomb blockade in nanostructured graphene.”

One of the main problems with spin-based quantum computers, Ensslin explains, is that spins won’t keep their direction indefinitely.

“Graphene turns out to be a material which is expected to overcome this,” Ensslin says. He is careful to explain that even though he and his peers have created a graphene quantum dot, extrapolations of how it would work in a quantum computer are still at the theory stage. “When you look at this theoretically, you find that 98 percent of carbon has no nuclear spin. This means that the coupling between nuclear spins and electron spins would be strongly reduced.”


However, March 2008 researchers found that spin and orbital motion of electrons in carbon nanotubes is coupled The findings have important implications for spin-based applications in carbon-based systems, entailing new design principles for the realization of quantum bits (qubits) in nanotubes and providing a mechanism for all-electrical control of spins in nanotubes.

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