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Physical Review Letter on halving the Casimir force
A paper by researchers of the Department of Physics and Astronomy has been published in the prestigious journal Physical Review Letters and highlighted in Nature Materials. The article ‘Halving the Casimir force with Conductive Oxides’ describes an experiment that demonstrates that the Casimir force in air can be reduced by a factor of two while remaining the dominant interaction mechanism.
The Casimir force is the attraction between two objects as a result of the quantum fluctuations of the electromagnetic field. The strength of this interaction depends on the reflectivity of the surfaces of the objects. Good metals give rise to a strong force, while between transparent dielectrics the interaction is weaker. This property has been for long regarded as a unique opportunity to engineer the Casimir force in Micro- and NanoElectroMechanical Systems (MEMS and NEMS). MEMS and NEMS, however, are typically designed to work in air, where dielectric materials quickly accumulate electrostatic charges. Those charges give rise to a Coulomb interaction that is difficult to control and that can easily overcome the Casimir force. One could thus think that there is no reason to tune the Casimir force in air, because, in any case, the overall interaction strength would not be significantly affected.
The paper shows, for the first time, that the latter statement is probably too pessimistic. The authors measured the force between two surfaces at very close separations. One of the two surfaces was made out of gold, while the other was covered with a transparent conductive oxide. As expected from theory, the Casimir force decreased by a factor of two when compared to gold-gold interaction. Interestingly, the oxide proved to drain the charges from the surfaces so efficiently that no residual electrostatic force could be observed. This finding implies that with these kinds of dielectrics there is ample room to tune the strength of the Casimir interaction in environments where MEMS and NEMS typically operate (i.e. in air), and that, since the Casimir force is still dominating, there is a good reason to tune it too!
Halving the Casimir force with Conductive Oxides
Physical Review Letters 103, 040402 (2009)
Material witness: Relaxing the vacuum – by Philip Ball
Nature Materials 8, p705 (2009), doi:10.1038/nmat2516
http://www.nature.com/nmat/journal/v8/n9/full/nmat2516.html
