Familiar materials behave differently at the smallest scales. In particular, diamonds, normally hard and brittle, grow strangely soft at the nanoscale. After years of not really understanding why, a team of physicists finally managed to decipher this behavior.
Using a custom-built electron microscope, the researchers discovered that there is a relatively weak chemical bond between the surface layer and the core of the tiny diamonds. When nanodiamonds are placed under pressure, strain is concentrated in the intermediate region between the diamond’s surface and core. As a result, the tiny diamonds did not fracture, but instead reacted like a flexible material, “enabling elasticity that would be nearly impossible in bulk diamond,” the researchers reported on their discovery in a recent Physical Review X paper.
“This hidden mechanism may play a role in the elasticity of brittle materials, suggesting that the rigid diamond prototype can tune its mechanical properties at the nanoscale,” said the research team, led by researchers from China’s Zengzhou University and Henan Academy of Sciences.
elastic points
The key mechanism behind this elasticity is the ratio of the number of atoms in the diamond’s surface layer and the diamond’s core. This ratio tends to be much larger for nanodiamonds, while larger diamonds have a smaller surface-to-core ratio. This relationship determines how diamond behaves under pressure, study lead author Chongxing Xiang, a materials scientist at Zengzhou University, told New Scientist.
In nanodiamonds, the increased surface-to-core ratio leads to weaker bonds between the surface atoms and the inner core in the so-called interfacial region. This weak region plays a “critical role” in the nanodiamond’s elastic properties, the paper explains. When subjected to pressure, this interfacial zone literally acts as a shaking chamber for the diamond, absorbing the shock on behalf of the surface and core atoms.
double check
For the study, the researchers designed an experiment that tested about 100 different diamonds in an isolated vacuum. Each diamond was baked at 212 degrees Fahrenheit (100 degrees Celsius) before the experiment, because smaller scales increase the risk of contaminants. In each session, individual nanodiamonds were clamped between two diamond indenters and connected to a sensor that measured how much the diamond softened without breaking.
Interestingly, the research team confirmed that size really does matter for the elasticity of nanodiamonds. For example, a 13-nanometer diamond had a stiffness similar to that found in typical jewelry, while a smaller 4-nanometer diamond was about 30 percent more stretchy. The researchers used their observations to devise an adapted mathematical model to measure diamond’s elasticity at the nanoscale.
Scientist’s best friend
To scientists, diamonds are more popular for their sheer versatility than for their dazzling visuals. To name a few examples, the capsules that store the hydrogen fuel in fusion reactors are made of diamond, and small imperfections in the diamond can cause or interrupt the fusion reaction. Physicists are also seriously considering diamonds as tiny data storage units in quantum devices. In less futuristic applications, diamonds are already a key component in major manufacturing processes.
It’s clear this idea was not lost on the researchers, who concluded that their discovery reveals “a practical knob for nanoscale devices.” [such as] Nanomechanical resonators, phononic devices, and diamond-based quantum sensors. ” Assuming the latest research is validated, this could mean researchers are now free to design more versatile and flexible components in sensitive technologies.
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