Although diamond is widely believed to be hard and unbendable, thin films have been found to exhibit elastic deformation - and this new property can have profound impacts on various applications.
A team of researchers from the City University of Hong Kong (CityU) has successfully demonstrated the uniform tensile elastic straining on a large scale for diamonds. Using a nanomechanical approach, researchers did it across microfabricated diamond arrays, showing the potential of these strained diamond films for potential applications in microelectronics, photonics, and quantum information technologies.
Dr. Lu Yang, Associate Professor from the CityU Department of Mechanical Engineering, with members of the collaborative study including researchers from the Massachusetts Institute of Technology (MIT) from the US and the Harbin Institute of Technology (HIT) in China. Results of their research are published in the journal Science on January 1, 2021.
"This is the first time showing the extremely large, uniform elasticity of diamond by tensile experiments," said Dr. Lu in a CityU press release.
370125 02: A 620-carat Sefadu Diamond is on display May 24, 2000, at the Ross-Simons jewelry store in Northbrook, IL. The giant Sefadu was discovered in 1970 near the town of Sefadu in the West African nation of Sierra Leone and is the largest rough diamond in existence today, the seventh-largest rough diamond ever to be found.
A New Application for Diamonds
Diamonds in the industrial setting are primarily known for their hardness, finding wide applications in cutting, drilling, or grinding requirements. However, recent advancements have also demonstrated the precious mineral as a high-performance electronic and photonic material, thanks to its exceptional electric charge carrier mobility, ultra-high thermal conductivity, high breakdown strength, and wide bandgap properties.
However, its natural properties - large bandgap and tight crystalline structure - also make the doping process near-impossible. Doping, or the process of introducing impurities to a substrate to control or modify its electric properties, is necessary to make it a feasible electronic and optoelectronic device. One way to work around this restriction is through a technique known as "strain engineering," where a large external force is applied to alter the diamond's band structure and, with it, its properties - a task previously considered "impossible" for the notoriously hard diamond.
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In 2018, Dr. Lu's team discovered that bending nanoscale diamonds is possible, although with extremely large strain forces - opening the potential of strain engineering on the material. To achieve this, researchers first fabricated micro-scale, single-crystalline diamond samples from solid single crystals. It resulted in bridge-like structures about one micrometer long at 300 nanometers wide, with ends slightly wider for gripping. Their samples are then subjected to iterations of continuous and controlled loading-unloading tensile tests, demonstrating a uniform deformation across the entire section instead of a localized deformation area.
Tunable Bandgap for Diamond Strips
Following the sample geometry achieved using the American Society for Testing and Materials (ASTM) standard, researchers were able to attain a uniform tensile strain of up to 9.7 percent, surpassing the previous 7.5 percent from their 2018 experiment. It recorded a bandgap reduction rate down from 5 electronvolts to 3 electronvolts, based on the researchers' spectroscopy analysis.
With their nanomechanical approach, researchers were able to open strain engineering as a possibility for microfabricated diamonds. It showed a measurable property change in the diamond band structure.
"I believe a new era for diamond is ahead of us," Dr. Lu added.
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