Nanoscale sensor offers insights into stress and strain

This is the claim of a team of researchers in the US whose work provides greater insights into the way pressure alters the physical, chemical and electronic properties of matter.

Valery Levitas - whose lab at Iowa State University specialises in experimental testing and computational modelling of high-pressure sciences - said the new sensing technology could help advance high-pressure studies in chemistry, mechanics, geology and planetary science.

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The development and demonstration of the technology is described in a paper published by Science. The lead author is Norman Yao, an assistant professor of physics at the University of California, Berkeley. Iowa State's Mehdi Kamrani, a doctoral student in aerospace engineering, is a co-author along with Levitas, a professor in aerospace engineering.

The paper describes how the researchers fit a series of nanoscale sensors - dubbed nitrogen-vacancy colour centres - into diamonds used to exert high pressures on tiny material samples. Typically, those "diamond anvil" experiments with materials squeezed between two diamonds have allowed researchers to measure pressure and changes in volume.

The new nanoscale sensor system reportedly allows researchers to image, measure and calculate six different stresses, providing a more comprehensive and realistic measure of the effects of high pressure on materials. The new tests also allow researchers to measure changes in a material's magnetism.

"This has been one of the key problems in high-pressure science," Levitas said in a statement. "We need to measure all six of these stresses across a diamond and sample. But it's hard to measure all of them under high pressure."

According to Iowa State University, Levitas' lab has conducted unique experiments by putting materials under high pressure and then giving them a twist, allowing researchers to reduce phase transformation pressure and search for new phases of matter, which may have technological applications.

The lab also conducts multiscale computer modelling for high-pressure diamond anvil experiments. Levitas said that experience with high-pressure simulations was why he was invited to collaborate with Yao's sensor project. Simulations made it possible to reconstruct fields of all six stresses in the entire diamond anvil, where they could not be measured, as well as verify experimental results. Levitas plans to use this sensor in his lab.

The nanoscale sensor enables "pursuit of two complementary objectives in high-pressure science: understanding the strength and failure of materials under pressure (e.g., the brittle-ductile transition) and discovering and characterising exotic phases of matter (e.g., pressure-stabilised high-temperature superconductors)," the researchers wrote in their paper.

The nitrogen-vacancy sensing technology has also been used to measure other material properties, such as electric and thermal characteristics. The researchers noted it "can now straightforwardly be extended to high-pressure environments, opening up a large range of experiments for quantitatively characterising materials at such extreme conditions."