Quantum force powers microslide

By Eric Smalley, Technology Research News

Researchers have coaxed two tiny metal parts to slide past each other powered only by the shapes of the parts and an oddity of quantum physics. The effect could be used to move microscopic machinery.

According to quantum physics, a vacuum is actually seething with zero-point energy, which is created by subatomic particles constantly popping in and out of existence. Many of the particles are photons, which means much of the energy is electromagnetic like light, x-rays and radio waves.

When two parallel plates are positioned closely enough that the gap between them is smaller than some electromagnetic wavelengths, some of the zero-point energy is shut out of the gap. Because there is more zero-point energy acting on the outer surfaces of the plates than the inner surfaces, the plates are drawn together, a phenomenon termed the Casimir effect.

Researchers at the University of California at Riverside and the Federal University of Paraíba in Brazil have found a way to use this effect to cause one surface to slide over another.

"The normal Casimir force acts perpendicular to the two interacting surfaces, pulling them together," said Umar Mohideen, an associate professor of physics at the University of California at Riverside. "The lateral Casimir force acts tangential to the two surfaces, leading to the horizontal sliding of one surface with respect to the other," he said.

In theory, if two corrugated plates are aligned parallel to each other and positioned closely enough, the Casimir force will come into play. But unlike two flat plates that are drawn together, the corrugated surfaces are at angles to the plate as a whole, and so when the surfaces are drawn together they move the plates laterally.

Because it is very difficult to keep two plates perfectly parallel when they are separated by less than a micron, the researchers replaced one of the plates with a gold sphere one-fifth of a millimeter in diameter. The researchers imprinted the sphere with corrugations by pressing the plate into it.

The researchers moved the plate sideways less than half a nanometer at a time and measured the lateral force exerted on the sphere at each step. A nanometer is one millionth of a millimeter. The researchers started with the plate and sphere separated by 221 nanometers. They increased the distance between them in 12 nanometer increments and repeated the lateral steps at each distance. As expected, the Casimir effect weakened as the distance increased.

The researchers are studying other shapes to use in their next experiment, said Mohideen. "The Casimir force depends strongly on the shape of the [surfaces] and can be repulsive or attractive," he said. "The force between two parallel metallic plates is attractive, [but] that between two hemispheres is repulsive."

As microelectromechanical systems (MEMS) become smaller, the Casimir effect could gum up the works. But researchers could also harness the effect. The lateral Casimir force could be used to provide sliding motion, said Mohideen.

The lateral Casimir effect is not surprising, said Steve Lamoreaux, a physicist at the Los Alamos National Laboratory. "[However], the experiment must have been extremely difficult and as such the result represents a real tour de force, no pun intended. This effect might be useful in nano-machines; it could be used as a lateral spring of some sort," he said.

"On the other hand, there is also a large force between the surfaces trying to pull them together, so there is a limitation on the usefulness of the effect," Lamoreaux said.

The lateral Casimir force could be applied in MEMS technology now but it is likely to take five to ten years before practical devices make use of it, said Mohideen.

Mohideen's research colleagues were Feng Chen of the University of California at Riverside, and Galina Klimchitskaya and Vladimir Mostepanenko of the Federal University of Paraíba in Brazil. They published the research in the March 11, 2002 issue of the journal Physical Review Letters. The research was funded by the National Science Foundation (NSF), the National Institute of Standards and Technology (NIST) and the Brazilian government.

Timeline:   5-10 years
Funding:   Government
TRN Categories:   Microelectromechanical Systems (MEMS); Nanotechnology
Story Type:   News
Related Elements:  Technical paper, "Demonstration of the Lateral Casimir Force," Physical Review Letters, March 11, 2002


May 1/8, 2002

Page One

Team spins mirror fibers

Light flashes fire up nanotubes

Quantum force powers microslide

Light boosts plastic magnet

Metal crystals cover glass


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