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October 12th, 2009
Named for a Dutch physicist, the Casimir effect governs interactions of matter with the energy that is present in a vacuum. Success in harnessing this force could someday help researchers develop low-friction ballistics and even levitating objects that defy gravity. For now, the U.S. Defense Department's Defense Advanced Research Projects Agency (DARPA) has launched a two-year, $10-million project encouraging scientists to work on ways to manipulate this quirk of quantum electrodynamics.
Nanoscale design is the most likely place to start and is also the arena where levitation could emerge. Materials scientists working to build tiny machines called microelectromechanical systems (MEMS) struggle with surface interactions, called van der Waals forces, that can make nanomaterials sticky to the point of permanent adhesion, a phenomenon known as "stiction". To defeat stiction, many MEMS devices are coated with Teflon or similar low-friction substances or are studded with tiny springs that keep the surfaces apart. Materials that did not require such fixes could make nanotechnology more reliable. Such materials could skirt another problem posed by adhesion: Because surface stickiness at the nanoscale is much greater than it is for larger objects, MEMS designers resort to making their devices relatively stiff. That reduces adhesion (stiff structures do not readily bend against each other), but it reduces flexibility and increases power demands.
Under certain conditions, manipulating the Casimir effect could create repellant forces between nanoscale surfaces. Hong Tang and his colleagues at Yale School of Engineering & Applied Science sold DARPA on their proposal to assess Casimir forces between miniscule silicon crystals, like those that make up computer chips. "Then we're going to engineer the structure of the surface of the silicon device to get some unusual Casimir forces to produce repulsion," he says. In theory, he adds, that could mean building a device capable of levitation.
Such claims emit a strong scent of fantasy, but researchers say incremental successes could open the door to significant breakthroughs in key areas of nanotechnology, and perhaps larger structures. "What I can contribute is to understand the role of the Casimir force in real working devices, such as microwave switches, MEMS oscillators and gyroscopes, that normally are made of silicon crystals, not perfect metals," Tang says.
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