The smallest electric motor in the world, devised by physicists at
UC Berkeley, is based on the shuttling of atoms between two metal droplets---one
large and one small---residing on the back of a carbon nanotube. An
electric current transmitted through the nanotube causes atoms to move
from the big to the small droplet. In effect, potential energy is being
stored in the smaller droplet in the form of surface tension.
the smaller drop grows so much that the two droplets touch. Then the
accumulated energy is suddenly discharged as the larger droplet reabsorbs
its atoms through the newly created hydrodynamic channel. This device
constitutes a "relaxation oscillator" with an adjustable operating frequency.
If the oscillator is attached to a mechanical linkage, it acts as a
motor and can be used to move a MEMS device in inchworm fashion (movie:
The peak pulsed power is 20 microwatts. Considering that the device
is less than 200 nm on a side, the power density works out to about
100 million times that of the 225 hp V6 engine in a Toyota Camry. Chris
Regan (email@example.com), a member of Alex Zettl's group at
Berkeley, reported these and related results at the recent APS meeting
in Los Angeles and in the 21 March 2005 issue of Applied Physics Letters.