Monthly Archives: July 2003

Physicists build world's smallest motor using nanotubes and etched silicon:

"It's the smallest synthetic motor that's ever been made," said Alex Zettl, professor of physics at UC Berkeley and faculty scientist at Lawrence Berkeley National Laboratory. "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." [...]

Because the rotor can be positioned at any angle, the motor could be used in optical circuits to redirect light, a process called optical switching. The rotor could be rapidly flipped back and forth to create a microwave oscillator, or the spinning rotor could be used to mix liquids in microfluidic devices.

The motor is about 500 nanometers across, 300 times smaller than the diameter of a human hair. While the part that rotates, the rotor, is between 100 and 300 nanometers long, the carbon nanotube shaft to which it is attached is only a few atoms across, perhaps 5-10 nanometers thick. [...]

The team's scanning electron microscope (SEM) can take pictures every 33 milliseconds and no faster, so they can't tell whether the rotor spins or flips faster than 30 times per second. "We assume you could go much, much faster than that, probably to microwave frequencies [a billion cycles per second]," Zettl said. "There's no way we can detect that right now, but in principle the motor should be able to run that fast." [...]

Interestingly, the rotor does not continue spinning for long once the electricity is turned off. It is so small that it has little inertia, so any tiny electric charges remaining on the device after it's turned off tend to stop the rotor immediately. "The nanoworld is weird - different things dominate," Zettl said. "Gravity plays no role whatsoever and inertial effects are basically nonexistent because things are just so small, so that little things like residual electric fields can play a dominant role. It's counter intuitive."