The most efficient diode ever made using carbon nanotubes has been unveiled, marking another step towards practical atomic electronics.

Carbon nanotubes - structures resembling rolled up cages made from interlinking carbon atoms - are extremely strong and are very good conductors of electricity.

Nano-diodes have been made previously by linking together two carbon nanotubes with different electronic properties. But now a more efficient nano-diode has been created by Ji-Ung Lee, and colleagues at the Nanotechnology Advanced Technology Program at General Electric's Global Research Center in Niskayuna, New York, US. The team used electric fields to change the properties of a single nanotube to make a diode.

In modern silicon circuits, diodes are made by introducing atomic impurities into the silicon -- a process called "doping". But this trick is more difficult to use with carbon nanotubes as it alters their fundamental properties.

"Instead of adding chemicals to dope the material, we used electric fields," Lee told New Scientist. He adds that this could lead to more adaptable types of nano-circuitry, as the electric fields can be varied to alter the properties of the diode, where doping is a fixed process.

The diode is a crucial electronic component since it controls the direction of an electronic current within a circuit.

The new diode showed performed better in tests than have previous nano-diodes.

Adaptable system

Adelina Ilie, a senior research fellow at Cambridge University's nanoscience centre says the technique developed by Lee's group has definite advantages. "It is significant because generally the diodes so far obtained haven't been controllable," she told New Scientist.

But Ilie adds that numerous obstacles must still be overcome for carbon nanotubes to become the basis for practical electronic components. "One of the big problems is reproducibility," she says. That is, that making nanotubes with predictable electronic properties remains a challenge.

Journal reference: Applied Physics Letters (vol 85, p 145)