- Diamonds can be bent, stretched and reformed to its original shape, if grown in tiny needle-like shapes.
- It could be stretched by as much as 9% without breaking.
- These results could open the new possibilities for diamond-based equipments.
Diamond is the hardest known material on Earth. Most of its superlative physical qualities come from the strong covalent bonding between its atoms. In particular, diamond has the highest thermal conductivity and hardness of any bulk material.
Now, an international team of scientists from MIT, Singapore, Hong Kong and Korea, has made a surprising discovery – diamonds can be bent, stretched and reformed to its original shape, if grown in tiny needle-like structures.
The tiny diamond needles (at nanometer-scale) look like rubber tips on the end of some toothbrushes. They could be stretched by as much as 9% without breaking, and then restored to their original form.
The conventional diamond in bulk can be stretched less than 1%. However, things work differently (in this case elastic deformation) when material is seen at the nanoscopic scale – they’ve unique and interesting properties compared to the bulk material with same composition.
How Did They Do This?
Diamond nano-needles with respect to the indenter tip
Researchers fabricated nanoscale diamond needles using a plasma-induced etching of diamond thin sheets deposited on silicon substrates. They controlled the size, shape, density and crystallinity of these tiny needles by suitable choice of growth parameters during deposition.
They etched the single crystalline diamond nano-needles from a oriented diamond sheet. The nano-needles were mounted on the silicon substrate inside a scanning electron microscope nano-indenter system. The indenter tip’s downward motion created a sideward displacement from the surface of the inclined tip, thus bending the needle.
More specifically, an indenter was used to horizontally push the tip of the needle as far as 442 nm, and the needle returned to its original position. When researchers tried to push the indenter even further, the needle snapped once the tip had been moved 464 nm.
A high-resolution transmission electron microscope was used to observe the needles. They discovered that the needles had a plane surface and a pristine single crystalline diamond shape along the growth orientation aligned with the axis of nano-needle.
They achieved 6% of maximum tensile strain for a single crystalline nano-needles: the peak tensile strain was 3.5% and mean maximum tensile strain was 3.3%.
Researchers also carried out a hybrid density functional theory-molecular dynamics measurement that revealed 13% of ideal maximum tensile strain along the direction, with carbon-carbon bond fracture above this threshold strain.
In addition to this, they also extracted the corresponding maximum elastic compressive strains. The local maximum compressive stress reached up to 110 GPa, with a diamond modulus of 1100 GPa. (GPa = GigaPascals)
These results could open the new possibilities for diamond-based equipments used in a wide range of applications like optoelectronics, data storage, sensing, drug delivery and biocompatible in vivo imaging.