Scientists have long been intrigued by the electrical properties of carbon nanotubes, those tiny straws of pure carbon measuring less than a hair's width across. Now one research team has unveiled an improved design for transistors based on the minuscule tubes, one that could substantially reduce the lower limit on transistor size.

The size of conventional transistors made of metal oxide semiconductors (MOS) has shrunk over the years and can now be as small as about 100 nanometers across. This reduction has allowed for an impressive increase in both the speed and power of a variety of electronics. By employing carbon nanotubes, a team led by Prabhakar R. Bandaru of the University of California at San Diego hopes to shrink transistor dimensions even more--down to just a few nanometers thick. "The small size and dramatic switching behavior of these nanotubes makes them candidates for a new class of transistor," he explains.

The novel transistors were first grown as regular, straight nanotubes. Using catalyst particles containing iron, the team then coaxed a second branch to grow out of the first tiny straw. The resulting y-shaped nanotubes carry current when attached to electrical contacts, and varying the amount of voltage applied to the stem controls the flow of electrons through the junction. The new approach improves on previous carbon nanotube-based transistors, in which separate components had to be added in. "We can synthesize functionality at the nanoscale, in this case to include the three elements of a circuit--the gate, source and drain," Bandaru says, "and we don't have to go to the trouble of making them separately and assembling them." A report detailing the results was published online yesterday by Nature Materials.