杏吧原创

Diamond is the hardest known naturally occurring material. It鈥檚 nearly impossible to compress or scratch. But it can bend.

While diamonds are hard to scratch, they鈥檙e not so difficult to shatter 鈥� usually, trying to bend a diamond results in it fracturing. Now, at the Massachusetts Institute of Technology and his colleagues have made tiny diamond needles that can bend by up to 9 per cent without breaking, and then snap back to their original position.

The researchers started by depositing a thin film of diamond onto a sheet of silicon. Then, they used high-energy ions to carve down into the film, leaving behind a forest of diamond nanoneedles standing a couple of micrometres tall and less than a micrometre across at their base.

The small size of these needles meant that they had very little room for defects in their crystal structure, which made it possible for them to bend without snapping, Dao says.

Bend and snap

The needles were bent using the pyramidal tip of a nano-indenter which pressed down so that the needles bent along one of the angled faces of the tip. The researchers were able to bend the tip about 450 nanometres away from where it started 鈥� about 20 per cent of the needle鈥檚 length 鈥� before it snapped off. The needles that were bent less than that sprang back to vertical.

The middle of the needle, where the bend began, stretched about 9 per cent, which is close to the theoretical maximum elastic stretching in diamond. It鈥檚 the largest elastic stretching of a diamond that鈥檚 ever been demonstrated.

Previous work has shown that when this strain exceeds 1 per cent, it can change the mechanical and chemical properties of the bent material due to changes in how it stores and transmits energy. 鈥淲hen maximum elastic strains can be changed in real time between 0 to 9 per cent in nanodiamonds, there is a lot of potential for exploring unprecedented material properties,鈥� says Dao.

He says that a bent diamond needle can be much more durable than a straight one, which might be useful for applications like delivering drugs directly into cells.

The key to bending a larger diamond 鈥� say, one you could see with the naked eye 鈥� would be to 鈥渞educe the defect level to be as low as that found in nanodiamonds,鈥� says Dao. 鈥淲e don鈥檛 know how to achieve that yet.鈥�

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