Small but perfectly-formed, as they say, the smallest synthetic motor ever made – an electric rotor on an axle 2,000 times shorter than the width of a human hair – has been built by scientists at the University of California’s Lawrence Berkeley National Laboratory.

Its inventors believe this micro-scale motor could enable breakthroughs in optical switching, chemical and motion sensing, and many other applications.

So small that its creators say it could ride on the back of a virus, the electrostatic motor is the latest development in the fast-growing but sometimes controversial field of nanotechnology, the manipulation of molecules at unbelievably tiny scales of a nanometre. If you’re not sure of your tiny measurements, a nanometre is one-millionth of a millimetre.

Already, nanotechnology has made itself felt in the manufacture of sunscreens and cosmetics and in new fabrics aimed at accelerating computer speeds. Future applications could be in biomedicine, including revolutionary new medical implants.

Nanotechnology is expected to expand into a multi-million pound industry over the next decade, and earlier this month the government announced a £90 million investment in the science over the next six years.

Built on a silicon chip, the gold rotor made at Berkeley, some 500 nanometres across, represents a significant milestone.

“It’s the smallest synthetic motor that has ever been made,” says its creator, Professor Alex Zettl, of the Lawrence Berkeley National Laboratory (LBNL). “Nature is still a little bit ahead of us – there are biological motors that are equal or slightly smaller in size – but we are catching up.”

Prof Zettl and his team of students had previously constructed transistors from nanotubes but, he explained, “this is the first device where you can put external wires on it and have something rotating; something you can control. We are pushing a lot of different technologies to the edge.”

Prof Zettl envisages the rotor being used in applications such as optical switching, which involves redirecting light within optical circuits, in microwave oscillators, or in mixing liquids in microfluidic devices used for analysing fluids.

While the actual rotating part of the motor – the gold rotor – is between 100 and 300 nanometres long, the carbon nanotube shaft to which it is attached is only a few atoms across, about 5-11 nanometres thick. When switched off, the rotor doesn’t continue to spin for long, as nano-devices have little inertia and any tiny residual electric charges stop it immediately.
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