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Illustration of tensile straining of microfabricated diamond bridge samples — Image Credit: Dang Chaoqun/ City University of Hong Kong)

ELASTIC DIAMONDS

Stretching diamonds can give them new electronic & optical properties

They can then be used for next-gen devices in microelectronics, photonics, & quantum information technologies

Although the precious metal is known for its high monetary value, diamond is also the hardest material found in nature. In other words, it does not have elastic properties at all… well almost — considering the stretchiest materials can reach tensile elastic strains of a few hundred percent, bulk diamond tops out at less than 0.4%.

A team of researchers led by the City University of Hong Kong (CityU) in collaboration with the Massachusetts Institute of Technology (MIT) and Harbin Institute of Technology (HIT) has now demonstrated for the first time that the nanoscale diamonds can be stretched to limits not possible before.

But one would wonder, what’s the use of creating this tensile straining? And the answer is that this changes the electronic and optical properties of the diamond, giving it the ability to be used in advanced devices like microelectronics, photonics, and quantum information technologies.

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“This is the first time showing the extremely large, uniform elasticity of diamond by tensile experiments. Our findings demonstrate the possibility of developing electronic devices through ‘deep elastic strain engineering’ of microfabricated diamond structures.”

~ Dr. Lu Yang, Lead Researcher

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Apart from the current industrial applications of diamonds in cutting, drilling, or grinding, the precious metal is also known for its ultra-high thermal conductivity, exceptional electric charge carrier mobility, high breakdown strength, and ultra-wide bandgap. And it is this key semi-conductor property of bandgap that researchers intend to change with this technique for better utilization of the metal.

CityU researchers built on their previous research, where they discovered changing the physical properties of diamond was possible with elastic strain engineering. They were able to stretch nanoscale diamond needles to tensile elastic strains of about 9% in the research conducted in 2018. In the latest study, they took this endeavor a step further.

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Image credit: Dang Chaoqun / City University of Hong Kong)

Researchers created bridge-shaped samples of diamond about 1,000 nanometers long and 300 nm wide — stretching them lengthwise. For the trials conducted, the diamond showed an elastic deformation of around 7.5% across the whole piece. Once the applied pressure was taken off, it returned to its original resting state.

Further tests were conducted to streamline the process by optimizing the shape of the samples, in an attempt to stretch the diamond even further. This effort yielded them an elastic deformation of about 9.7%, which the researchers believe is the theoretical elastic limit of the diamond. So what properties did these tests change and how could they be useful?

The team then performed density functional theory (DFT) calculations to estimate the impact of elastic straining from 0 to 12% on the diamond’s electronic properties. The tests showed that as tensile strength increased, the bandgap of the diamond generally decreased — the diamond essentially became more electrically conductive.

It peaked at a 2 electronVolt drop (from 5eV to 3eV) when under about 9% strain. Using electron energy-loss spectroscopy analysis, the researchers were able to verify this bandgap-decreasing trend in the diamond samples. Researchers believe that these changes are continuous & reversible and can lead to useful applications in micro/nanoelectromechanical systems (MEMS/NEMS), strain-engineered transistors, to novel optoelectronic and quantum technologies.

Complete Research was published in the Journal of Science.

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