Published online 14 August 2005 | Nature | doi:10.1038/news050808-17

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Carbon nanotubes could make for smaller circuits.

The tiny Y-shaped nanotube could mark a big step in electronics. © P. Bandaru/UCSD/Nat. Mater.

The first electrical switch made entirely from carbon nanotubes has been unveiled. Its inventors hope that it could help to replace silicon chips with faster, cheaper, smaller components.

The device is a Y-shaped nanotube that behaves like a transistor, such as those found in every electronic device in your home. Current flowing from one branch to another can be switched on and off by applying a voltage to the third. The switching is perfect - the current is either on or off, with nothing in between.

"The small size and dramatic switching behaviour of these nanotubes makes them candidates for a new class of transistor," says Prabhakar Bandaru, a materials scientist at the University of California, San Diego, who led the team of inventors.

The scientists make their Y-shaped nanotubes by adding a titanium-iron catalyst to a pot of straight nanotubes while they are growing. When a catalyst particle sticks to the side of a nanotube, it forms the base of a new branch, they report in Nature Materials1.

Smaller chips, bigger leaks

Conventional transistors are built from layers of semiconducting materials, such as silicon. Better manufacturing methods have led to ever-smaller chips, packing enormous amounts of computing power into desktop machines.

But as the components shrink, they start to leak electrical current. This causes overheating, wastes power, and can make some switches read 'on' when they should be 'off'. It seems that the silicon chip cannot get much smaller.

So scientists are looking for ways to make carbon nanotubes do the same job. These rolled up sheets of carbon atoms conduct electricity and take up a lot less room than silicon circuits, measuring just a few billionths of a metre across.

Nanotubes can also be made using cheaper chemical methods that avoid the laborious layering and etching used to make today's circuits. "This allows us to go for devices with much smaller size but much more complex functionalities," explains Hongqi Xu, a physicist from Lund University in Sweden.

Build gates

Scientists have already made logic circuits using nanotubes2,3,4, but these required metal 'gates' to control the flow of charge. Making such devices requires several steps, so it is unlikely that they could compete economically with conventional electronics, says Xu.

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But the gates in the new device are part of the nanotube's structure, making it fully self-contained, explains Bandaru. He adds that the catalyst particle sitting at the centre of the nanotube could be tweaked to change the switching properties of the device - making it switch at different voltages, for example.

The team is now trying to extend the alphabet of branched nanotubes with T- and X-shapes that could allow different functions. "What really keeps me enthused is that there are so many possibilities," says Bandaru.