A WEIRD quantum effect could come to plague designers of micromachines, say
scientists at Bell Labs in New Jersey. They have found that a phenomenon known
as the Casimir effect can make parts of a microscopic see-saw move
spontaneously.
Engineers will have to take the Casimir effect into account, they say, or
else the revolutionary molecule-sized machines now being planned could come
unstuck. But there鈥檚 a plus side too: the effect could be harnessed to form a
nano-scale spring.
Nanotechnology is an emerging field in which scientists hope to build
machines that have parts just a few thousand atoms across. Such devices could
one day cruise your bloodstream dispensing drugs, or patrol your mattress
exterminating bed bugs.
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But when nano-devices are built small enough, previously ignored quantum
effects come into play, says Hobun Chan at Bell Labs, part of Lucent
Technologies. The phenomenon he鈥檚 worried about was predicted in 1948 by the
Dutch physicist Hendrik Casimir, who reasoned that in the quantum world even a
vacuum isn鈥檛 devoid of energy.
Instead, it contains virtual photons and other particles which pop in and out
of existence. But in a small space, only photons whose wavelengths fit into the
space a whole number of times can appear. As a result, the gap between two very
closely spaced uncharged plates in a vacuum contains fewer particles than the
space outside. Casimir reasoned that this difference should create a pressure
that pushes the plates together. Steve Lamoreaux at Los Alamos National
Laboratory in New Mexico eventually demonstrated Casimir鈥檚 effect in 1996 by
measuring the attraction between two very closely spaced plates
(New Scientist, 25 January 1997, p 16).
Chan and his colleagues wondered what this effect might do to micromachines.
To find out, they manufactured a tiny see-saw
(see Diagram), to see if it was
affected by quantum fluctuations in the vacuum. Chan slowly lowered a conducting
sphere towards the see-saw. At a distance of about 500 nanometres, the see-saw
began to swing towards the sphere, until they touched. Similar distances would
commonly separate the components in many micromachines now being designed, Chan
warns. 鈥淚t could certainly lead to malfunction.鈥�
And the smaller the machine, the worse the problem gets. 鈥淎t a separation of
10 nanometres, the pressure is as much as 1 atmosphere,鈥� he says.FIG-mg22783001.JPG
Boris Spivak, an expert on quantum effects in metals at the University of
Washington in Seattle, says the Bell Labs work鈥攖o be published in the
journal Science鈥攃ould help reveal how heat and gravity affect
micromachines. 鈥淚t鈥檚 fantastic they had the sensitivity to measure this,鈥� he
says.
But the Casimir effect could also prove useful in nano-design. It might be
possible, says Chan, to make a switch that clamps shut in response to the subtle
vibrations of background noise. Lamoreaux is more enthusiastic. 鈥淚t鈥檚 a ready
energy storage mechanism, you can use it anywhere you need a spring,鈥� he says.