Material one thousand times thinner than paper withstands the squeeze to retain its shape

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These ultra-thin plates are able to retain their shape after being bent and squeezed by a human hand

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Ultra-thin and lightweight, yet durable beyond the lab setting. These are the desirable attributes for scientists in pursuit of the next generation of versatile, high-performing wonder materials. Emphasizing one without compromising the others has been a tricky balancing act for engineers, but one team is now claiming a significant breakthrough. Its first-of-its-kind nanoscale plate is one thousand times thinner than paper and still manages to maintain its shape after being bent and twisted by a human hand.

With the thickness of just a single atom, remarkable strength and conductivity of heat and electricity, graphene has led the charge toward the new age of advanced materials. However, lacking a solid shape in its original form, two-dimensional materials like graphene generally need to be combined with peripheral supports like a plate or a frame to prevent them from curling up on themselves and becoming unusable. This in turn adds to the weight, detracting from one of the materials' biggest strengths.

So researchers at the University of Pennsylvania set out to develop a material that could retain its shape, even after being bent or squeezed with a human hand, without the aid of a supporting structure. They approached this by designing their plates with a corrugated, honeycomb pattern, giving them a three-dimensional, rather than planar shape, albeit at the nanoscale.

The plates were made from aluminum oxide, which was deposited one atomic layer at a time, resulting in material between 25 and 100 nanometers thick that exhibited exceptional rigidity.

"Aluminum oxide is actually a ceramic, so something that is ordinarily pretty brittle," says Igor Bargatin, leader of the research. "You would expect it, from daily experience, to crack very easily. But the plates bend, twist, deform and recover their shape in such a way that you would think they are made out of plastic. The first time we saw it, I could hardly believe it."

The new material could potentially overcome a number of limitations in using other flat, less rigid films beyond the lab, which have a tendency to conform and stick to surfaces, where they are then hard to remove. These are also more vulnerable to tears and cracks that spread across the entire material, whereas the honeycomb pattern means that if a crack does appear in the aluminum oxide plates, it can be contained to one small section by the vertical walls.

In developing its ultra-thin, robust material, the team is hopeful it can help solve structural engineering problems in fields where weight is key, such as aviation. One specific example offered is to make wings for insect-inspired flying robots.

"The wings of insects are a few microns thick, and can't be thinner because they're made of cells," says Bargatin. "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 meter."

The research was published in the journal Nature Communications.

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