Originally Published MPMN March 2009

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Manipulating Casimir Force Improves Nanodevice Manufacturing

Stephanie Steward

An invisible force causing attractive and repulsive reactions between two surfaces, the Casimir-Lifshitz (C-L) force is always present between all materials, but is only measurable on the nanoscale. Recent advances in instrumentation, however, have enabled more-accurate measurement of the phenomenon. As a result, researchers experimenting with this force have learned how to manipulate it to an extent. In doing so, they’ve opened up a world of possibilities for future nanodevice manufacturing.

The attractive C-L force causes materials to stick together, which can create friction between nanodevice components and prevent them from functioning properly. In contrast, the repulsive C-L force can repel two materials so that one material is, in effect, suspended above the other without any support.
“From a manufacturing point of view, one could try to use these forces for self-assembly of parts made out of different materials,” says Jeremy Munday, a postdoctoral researcher at the California Institute of Technology (Pasadena, CA; www.caltech.edu) and coauthor of a study published in the January issue of the journal Nature. Munday collaborated with Federico Capasso at Harvard University (Cambridge, MA; www.harvard.edu), who led the study, and V. Adrian Parsegian, senior investigator at the National Institutes of Health (Bethesda, MD; www.nichd.nih.gov), who coauthored the paper.
Because many micromechanical devices have not yet reached the submicron scale, few engineers have had to factor these forces into their designs. “However, with continued miniaturization, these forces will need to be considered in the design phase of devices,” says Munday. “By learning how to modify this force, it can be incorporated into the design of the devices rather than being the hindrance it currently is.”
For their experiment, the researchers used a gold-coated sphere and, employing a modified version of an atomic force microscope, measured the force between the sphere and either a gold or a silicon dioxide plate in a bromobenzene fluid. The gold plate produced an attractive force, whereas the silicon dioxide plate produced a repulsive force. In order to find more materials that can produce these results, more optical data are needed, says Munday. However, PTFE is a good candidate to serve as the low dielectric function material, while many metals work for the high dielectric material, he adds.
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