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The new transistors begin life as straight nanotubes before the addition of titanium-modified iron catalyst particles prompts new growth, like a branch from a tree, to create a Y-shaped tube as the catalyst is absorbed at the junction of the stem and the new growth.

When electrical contacts are attached electrons travel into one arm of the Y, hop onto the catalyst particle, and then hop to the other arm and flow outward. By applying a voltage to the stem this movement can be controlled or, as chip engineers say, gated: a positive charge stimulates the flow creating an 'on' signal, while an 'off' signal is created by reversing the current so the movement of electrons stops.

Currently the minimum thickness of transistors is about 100 nanometers; Y-shaped nanotubes can be made as thin as a few nanometers.

'The small size and dramatic switching behaviour of these nanotubes makes them candidates for a new class of transistor,' said Prabhakar

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Bandaru, engineering professor at the University of California San Diego.

He added that the phenomenon effectively makes Y-shaped nanotubes the smallest ready-made transistor yet, with rapid switching speeds and possible three-way gating capability. In earlier attempts to make carbon nanotube-based transistors, separate metal gates were added rather than built in.

'We think this discovery extends the paradigm of nanotechnology beyond just making things small,' said Bandaru. 'We can synthesise functionality at the nanoscale, in this case to include the three elements of a circuit - the gate, source, and drain - and we don't have to go to the trouble of making them separately and assembling them.'

The research team - Bandaru, fellow professor Sungho Jin and student Chiara Daraio - will now experiment with other catalyst particles to tailor the gating properties at the Y-junctions. It will also look at extending the alphabet of junctions to include T and X.

'If we can easily fabricate, manipulate, and assemble these nano-devices on a large scale they could become the basis of a new kind of transistor and nanotechnology,' said Bandaru.

As well as size, nanotubes have one further advantage over silicon technology. The cheap chemical process used to make then contrasts with the complex process of etching and layering that goes into making silicon circuits.

The researchers explain their findings in this (Real) video.