Diamond is the hardest known naturally occurring material. It’s nearly impossible to compress or scratch. But it can bend.
While diamonds are hard to scratch, they’re not so difficult to shatter – 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.
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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 – about 20 per cent of the needle’s length – 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’s the largest elastic stretching of a diamond that’s 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. “When 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,” 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 – say, one you could see with the naked eye – would be to “reduce the defect level to be as low as that found in nanodiamonds,” says Dao. “We don’t know how to achieve that yet.”
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Article amended on 11 May 2018
We corrected what did the bending.
