The Reins of Casimir: Patterned Nanoscale Structures May Control Quantum Effect

Quantum forces, most notably the Casimir effect, can play havoc if you need to keep closely spaced surfaces from coming together. Scientists that work to engineer nanoscale machines know this only too well and now, they may have found a way to counteract this effect. It turns out that these sticky effects can be increased or lessened by patterning one of the surfaces with nanoscale structures. The findings could help researchers create small mechanical parts that never stick together, quantum computers and could help them study gravity at the microscale.

One of the insights of quantum mechanics is that no space, not even outer space, is ever truly empty. It's full of energy in the form of quantum fluctuations, including fluctuating electromagnetic fields that seemingly come from nowhere and disappear just as fast. Some of this energy isn't able to "fit" in the submicrometer space between a pair of electromechanical contacts, though. More energy on the outside than on the inside can result in a kind of "pressure" called the Casimir force. This, in turn, can be powerful enough to push the contacts together and stick.

Prevailing theory describes the Casimir force between featureless, flat surfaces and even between most smoothly curved surfaces. However, this theory fails to account for the interactions observed between less conventional surfaces--such as the ones in this particular experiment.

"In our experiment, we measured the Casimir attraction between a gold-coated sphere and flat gold surfaces patterned with rows of periodic, flat-topped ridges, each less than 100 nanometers across, separated by somewhat wider gaps with deep sheer-walled sides," said Vladimir Aksyuk, one of the researchers, in a news release. "We wanted to see how a nanostructure metallic surface would affect the Casimir intereaction, which had never been attempted with a metal surface before."

So what did they find? It turns out that when the scientists increased the separation between the surface of the sphere and the grooved surface, the Casimir attraction decreased much more quickly than expected. When the scientists moved the sphere farther away, the force fell by a factor of two below the theoretically predicted value.

The findings are important for the future of nanoscale structure. More specifically, they show how Casimir attraction can impact different surfaces. This could pave the way for a new model to describe what the scientists observed in their experiment.

The findings are published in the journal Nature Communications.