High-impact research at CityU

In a world first, an international research team, led by City University of Hong Kong, has discovered that diamonds at nanoscale can undergo ultralarge, fully reversible elastic deformation – a finding that could have a profound impact on the nanotechnology and biomedical fields, and even quantum information technologies.

City University of Hong Kong

Led by Dr Lu Yang, associate professor in the department of mechanical and biomedical engineering at CityU, the research team demonstrated that when diamond was downsized to nearly 100 nanometres in diameter, which is about one six-hundredth the size of human hair, up to around 9 per cent of tensile elastic strain was recorded for single crystalline samples. The figure is very close to the maximum theoretically achievable strain for an ideal diamond crystal. In contrast, bulk diamond is usually regarded as “undeformable”, with only 0.1 to 0.35 per cent strains having been recorded in the past.

This groundbreaking discovery was published in the journal Science in April 2018 under the title “Ultralarge elastic deformation of nanoscale diamond”. It was jointly presented by Amit Banerjee and Zhang Hongti, two of the first co-authors of the paper, supervised by Dr Lu. The research team comprises materials scientists and mechanical engineers from the Massachusetts Institute of Technology, Ulsan National Institute of Science and Technology and Nanyang Technological University.

In this project, Dr Lu and his team aimed to characterise the mechanical properties of nanoscale diamonds by using their unique, in situ nano-indenter platform inside electron microscopes. The diamond samples were fabricated by Professor Zhang Wenjun, of CityU’s department of materials science and engineering.

Diamond, the hardest natural material, is often used for cutting and drilling tools as well as to test other materials’ mechanical properties. To tackle the predicament of “diamond against diamond” for this unusual experiment, Dr Lu developed the novel “push to bend” test to exert force on to the diamond nanoneedle from the slant surface of a nano-indenter tip.

Ultralarge elastic deformation of nanoscale diamond

The large deformation observed is fully reversible in nature, which implies that the diamond material retains the ability to instantaneously revert back to its original shape when the force causing the deformation is withdrawn, meaning that diamond can be elastic.

When this surprising result was first discovered in his lab, Dr Lu said it was “extremely exciting”. “This finding would fundamentally change our common understanding of diamond,” he explained.  

The research holds great promise because diamond is compatible with the human body. One area of possible future exploration is diamond needle-based drug delivery to human cells. “Our discovery on nanodiamond’s elasticity can help to make such intracellular delivery more durable and cost-effective,” said Dr Lu, noting that diamond needles are “not as brittle as we perceived”.

“The next generation of information technology could be also based on diamond,” he said. “Nanoscale diamonds with well-controlled point defects can be used for quantum computing and quantum information processing.

“Our discovery concerning diamond’s nano-sized characteristics allows manufacturers to produce highly reliable and efficient diamond resonators and sensors for faster data storage and transfer. Future computers will be smaller, lighter and faster,” Dr Lu predicted. 

This novel finding may pave the way for diamond’s practical applications in nanomechanical engineering, biomedical engineering, photonics, opto-electronics, and ultra-strength materials.

The research was funded by the Research Grants Council and National Natural Science Foundation of China.