World`s tiniest motor could ride on the back of a virus

A Californian physicist has created the world`s smallest motor - a machine so tiny that 300 of them would be needed to span the diameter of a human hair. The electrostatic motor is just 500nm in diameter, with a gold rotor that is 100-300nm long, and a shaft that is just a few atoms wide (5-10nm).

"It`s the smallest synthetic motor that`s ever been made," says Alex Zettl, a physics professor at the University of California, Berkeley. "Nature is still a little bit ahead of us - there are biological motors that are equal or slightly smaller in size - but we`re catching up."

Although the nanomotor is still at the experimental stage, such machines could, in future, have applications such as mixing fluids and switching optical circuits.

One unexpected problem that Zettl and his colleagues encountered while developing the motor is that it is impossible for them to tell how fast the rotor is spinning. Their scanning electron microscope can only take a picture of the motor once every 33ms, so they cannot tell whether it is spinning faster than 30Hz. In theory, the motor should be able to run at GHz frequencies.

Once power is removed from the motor, it stops spinning almost immediately because it has almost no inertia.

"The nanoworld is weird - different things dominate," Zettl explains. "Gravity plays no role whatsoever, and inertial effects are basically non-existent because things are just so small that little things like residual electric fields can play a dominant role. Its counter-intuitive."

Zettl expects to reduce the size of his motor even further - perhaps by a factor of five.