'Novel nano-guitar string that plays on its own created'

Scientists have created a nano-electronic circuit using a tiny suspended wire -- resembling a vibrating guitar string -- which vibrates without any external force.

The experiment, described in the journal Nature Physics, shows how a simple nano-device can generate motion directly from an electrical current.

The researchers at Lancaster University and the University of Oxford in the UK took a carbon nanotube, which is wire with a diameter of about three nanometres, roughly 100,000 times thinner than a guitar string.

They mounted it on metal supports at each end, and then cooled it to a temperature of 0.02 degrees above absolute zero.

The central part of the wire was free to vibrate, which the researchers could detect by passing a current through it and measuring a change in electrical resistance.

Just as a guitar string vibrates when it is plucked, the wire vibrates when it is forced into motion by an oscillating voltage.

When the researchers repeated the experiment without the forcing voltage, the wire oscillated of its own accord under the right conditions.

The nano-guitar string was playing itself, the researchers said.

"It took us a while to work out what was causing the vibrations, but we eventually understood," said lead researcher Edward Laird of Lancaster University.

"In such a tiny device, it is important that an electrical current consists of individual electrons. The electrons hop one by one onto the wire, each giving it a small push.

"Usually these pushes are random, but we realised that when you control the parameters just right, they will synchronise and generate an oscillation," Laird said.

The nanotube is far thinner than a guitar string, so it oscillates at much higher frequency -- well into the ultrasound range so no human would be able to hear it, the researchers said.

"However, we can still assign it a note. Its frequency is 231 million hertz, which means it's an A string, pitched 21 octaves above standard tuning," said Laird.

The nano-oscillator could be used to amplify tiny forces, such as in novel microscopes, or to measure the viscosity of exotic quantum fluids, according to the researchers.