Engineering 101

Did You Know That Diamonds Stretch?

Diamond, at 10 on the Mohs scale, is the hardest material in nature. Now, the results of joint research led by the City University of Hong Kong (CityU) shows potential for the use of strained diamonds in advanced functional devices in microelectronics, photonics, and quantum information technologies. These uses were previously impossible because of their inherent hardness.

Co-led by Dr Lu Yang, Associate Professor in the Department of Mechanical Engineering (MNE) at CityU, and researchers from Massachusetts Institute of Technology (MIT) and Harbin Institute of Technology (HIT), the team demonstrated the use of deep elastic strain engineering of microfabricated diamond structures to possibly develop electronic devices. It is the first time demonstrating the extremely large, uniform elasticity of diamond by tensile experiments. The findings were recently published in the scientific journal Science, titled “Achieving large uniform tensile elasticity in microfabricated diamond“.

Diamond is a high-performance electronic and photonic material due to its ultra-high thermal conductivity, exceptional electric charge carrier mobility, high breakdown strength, and ultra-wide bandgap. Wide bandgap allows the operation of high-power or high-frequency devices.

Until now, however, the large bandgap and tight crystal structure inherent in diamond, made it difficult to dope—to modulate the semiconductors’ electronic properties during production. Strain engineering, applying a large lattice strain to change the electronic band structure and functional properties, was considered impossible for diamond because of its extremely high hardness.

Dr Lu and his team discovered that nanoscale diamond can be elastically bent with unexpected large local strain, suggesting the change of physical properties in diamond through elastic strain engineering is possible. The team first microfabricated single-crystalline diamond samples from a solid diamond single crystal. The samples were in a bridge-like shape, and the bridges were then uniaxially stretched within an electron microscope. Under cycles of continuous and controllable loading-unloading of quantitative tensile tests, the diamond bridges demonstrated a highly uniform, large elastic deformation of about 7.5% strain across the whole gauge section of the specimen, recovering their original shape after unloading.

Using the American Society for Testing and Materials (ASTM) standard, they achieved a maximum uniform tensile strain of up to 9.7%, and to demonstrate the strained diamond device concept, the team also realized elastic straining of microfabricated diamond arrays.

By using a nanomechanical approach, the team demonstrated that the diamond’s band structure can be changed, and the changes can be continuous and reversible. Applications range from micro/nanoelectromechanical systems (MEMS/NEMS), strain-engineered transistors, to novel optoelectronic and quantum technologies.

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