Researchers make world’s thinnest plates that can be picked up by hand

Researchers at the University of Pennsylvania claim to have created the thinnest plates that can be picked up and manipulated by hand.

Thin materials, like cling film, immediately curl up on themselves and get stuck in deformed shapes if they are not stretched on a frame or backed by another material. Despite being thousands of times thinner than a sheet of paper and hundreds of times thinner than cling film or aluminium foil, The Penn researchers’ corrugated plates of aluminium oxide are said to spring back to their original shape after being bent and twisted.

Being able to stay in shape without additional support is said to allow this material, and others designed on its principles, to be used in aviation and other structural applications where weight reduction is key.

"Materials on the nanoscale are often much stronger than you'd expect, but they can be hard to use on the macroscale" Igor Bargatin, assistant professor of mechanical engineering and applied mechanics in Penn's School of Engineering and Applied Science, said. "We've essentially created a freestanding plate that has nanoscale thickness but is big enough to be handled by hand. That hasn't been done before."

The researchers' plates are between 25 and 100nm thick and are made of corrugated aluminium oxide, which is deposited one atomic layer at a time to achieve precise control of thickness and shape. Once finished, the plates' corrugation provides enhanced stiffness which guards against the common flaw in un-patterned thin films, where they curl up on themselves.

The team’s material is also said not to conform and stick to surfaces and is resistant to cracking and tearing due to the corrugation.

The corrugated pattern of the plates is an example of a relatively new field of research: mechanical metamaterials. Like their electromagnetic counterparts, mechanical metamaterials achieve otherwise impossible properties from the careful arrangement of nanoscale features, such as stiffness and strength, rather than their ability to manipulate electromagnetic waves.

Other existing examples of mechanical metamaterials include ‘nanotrusses’, which are exceptionally lightweight and robust three-dimensional scaffolds made out of nanoscale tubes. The Penn researchers' plates take the concept of mechanical metamaterials a step further, using corrugation to achieve similar robustness in a plate form and without the holes found in lattice structures.

That combination of traits could be used to make wings for insect-inspired flying robots or in other applications where the combination of ultra-low thickness and mechanical robustness is critical.

"The wings of insects are a few microns thick, and can't get thinner because they're made of cells," Bargatin said. "The thinnest man-made wing material I know of is made by depositing a Mylar film on a frame, and it's about half a micron thick. Our plates can be ten or more times thinner than that, and don't need a frame at all. As a result, they weigh as little as than a tenth of a gram per square metre."

Tom Austin-Morgan

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