This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: For the first time, researchers in Japan have directly mapped several components of the stress field surrounding an atomic-scale flaw in the crystal structure of diamond. Led by Tokuyuki Teraji at Japan's National Institute for Materials Science, the team achieved its result using nitrogen-vacancy (NV) centers in diamond, whose spin states respond differently to stress depending on how they are oriented relative to the stress field.
Published in Applied Physics Letters, the technique validates an 80-year-old theory about how miniature stress fields are distributed in diamond. It could also help improve the processes used to manufacture the high-quality diamond demanded by emerging technologies. Even in otherwise orderly crystals like diamond, atomic-scale flaws can always be found, where neighboring rows of atoms are misaligned with each other.
Named "dislocations," these flaws create minute stress fields which ripple out through the surrounding atoms. Across the whole lattice, they can strongly affect the material's mechanical, electrical and magnetic properties. More than 80 years ago, physicists used elasticity theory to derive a mathematical description of these stress fields, known as a "stress tensor," which defines the stress at any given point surrounding a dislocation.
Since then, this description has underpinned our understanding of how dislocations behave, from the energy they store to the forces they exert on each other. However, measuring these microscopic stress fields directly has proven far more challenging: existing techniques can capture only some aspects of the stress, so the theory has never been fully tested. Recently, this difficulty has become more pressing in the design of next-generation power and quantum devices.
Many of these technologies rely on growing high-quality crystals in the lab: a process that demands exquisite control. Without a reliable way to measure dislocation stress fields directly, uncertainties can arise about how these defects affect a crystal's properties, preventing materials from reaching their full potential. In the study, Teraji's team used NV centers as tiny sensors of the stress surrounding a dislocation.
These defects form when a carbon atom in the diamond lattice is replaced by a nitrogen atom, sitting next to an empty lattice site. "We realized that 'stress imaging' within the diamond crystal is essential for achieving even higher crystal quality," Teraji says. "To achieve this, we adopted an approach that combined the optimization of quantum sensing technology with the adjustment of the nitrogen concentration within the crystal." NV centers are especially useful in quantum sensing since the spin states of unpaired electrons associated with them are highly sensitive to their local environments, including mechanical stress.
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