Breakthrough Research Heralds a New diamond age

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A joint research team led by the City University of Hong Kong (CityU) has successfully achieved elastic straining of the diamond at an unprecedented level, a breakthrough that heralds a new diamond age in the utilization of the gemstone in microelectronics, photonics, and quantum information technologies.

The research results show that microfabricated single-crystalline diamond tensile sample can attain a maximum uniform elastic strain of up to 9.7%, which is close to the theoretical elastic deformation limit of a diamond.

These groundbreaking results were produced by a team co-led by Dr Lu Yang, Associate Professor in the Department of Mechanical Engineering (MNE) at CityU, in collaboration with experts from Massachusetts Institute of Technology (MIT), Harbin Institute of Technology (HIT), and others.

Their findings have been published in the prestigious journal Science under the title “Achieving large uniform tensile elasticity in microfabricated diamond”.

With its ultra-high thermal conductivity and exceptional carrier mobility, diamond is not only the hardest material in nature but also a promising electronic material that can tolerate high power and high-frequency applications.

“We microfabricated single-crystalline diamond into bridge-like structures from a solid piece of diamond crystal with a well-defined crystalline orientation, and achieved sample-wide large uniform strains under our tensile platform,” said Dr Lu.

“We also showed that in the process of uniaxial tensile straining, the change in the crystal structure of diamond will reduce its electronic bandgap, making its application in electronic devices possible.”

Experiment results found that diamond bridges of about 1 micrometer in length and 100-nanometer thickness can sustain a highly uniform elastic strain distribution of about 7.5% across the sample, as characterized by Dr Lu’s tailor-made nanomechanical tensile platform in a controllable manner.

By further optimizing the sample geometry according to the American Society for Testing and Materials (ASTM) standard, the team demonstrated that some bridge samples achieved a maximum tensile strain of up to 9.7%. “It surpasses the local maximum strain value in our 2018 research,” said Dr. Lu.

To assess the impact of such large elastic strains on the electronic property of diamond, the team performed theoretical calculations according to the applied tensile strains in experiments and found that the bandgap of the diamond generally decreases as the tensile strain increases, with the largest bandgap reduction rate down from about 5 eV (electron volt) to 3 eV at about 9% strain along a certain crystallographic orientation, which would greatly facilitate diamond’s electronics applications and boost a device’s performance.