The Signal
NV Centers Map Stress Around One Diamond Dislocation
Researchers used nitrogen-vacancy centers to map four stress quantities around a single dislocation in diamond. Their measurements agree with elasticity theory and resolve stress variations near 10 megapascals.
Quantum.world Team · Written with AI · fact-checked ·
Stress variations of about 10 megapascals around one diamond defect were resolved with measurement errors near 1 megapascal. Researchers used nitrogen-vacancy (NV) centers in a diamond film to map the defect’s stress pattern and compare it with a theory developed more than 80 years ago.
The work by Takeyuki Tsuji, Shunta Harada and Tokuyuki Teraji now appears in Applied Physics Letters. The team mapped three shear components and the trace—the sum of the three axial components—around a single 45-degree dislocation. The measured pattern agreed with elasticity theory, giving an experimental check on predictions that conventional methods have struggled to test directly.
Four stress quantities, measured around one defect
A dislocation is a line defect in a crystal: the regular arrangement of atoms is disrupted along a narrow seam. Its surrounding stress can affect a material’s mechanical, electrical and magnetic properties. A stress tensor has six independent components, but the researchers’ NV method recovered four quantities: the three shear components and the trace, rather than all six separately.
The researchers grew a roughly 20-micrometer-thick, carbon-12-enriched diamond film containing nitrogen. NV centers—each formed by a nitrogen atom next to a vacant site in the crystal—occur in four possible orientations. Because their spin resonances shift differently with stress depending on orientation, the team could use the shifts to separate the mapped quantities.
They used a confocal microscope to read the NV fluorescence while applying microwaves, and used Ramsey sequences to improve the precision of resonance measurements. The team scanned an 8-by-8-micrometer area in a 10-by-10 grid, after identifying the defect as a single 45-degree dislocation through X-ray topography and measurements of its direction. The film’s NV concentration was estimated at about 0.05 parts per million.
Ramsey measurements resolve the dislocation’s pattern
A magnetic field of about 7.2 millitesla separated the NV resonances for measurement. Near the defect, one resonance shifted by about 0.6 megahertz. Across the mapped area, the trace varied by approximately ±0.03 gigapascals, while each of the three shear components varied by about ±0.01 gigapascals. The team reports measurement errors roughly ten times smaller than those variations, or about 1 megapascal.
The authors write: “The observed distributions exhibited good agreement with predictions from elasticity theory, thus providing experimental validation of this theoretical framework.” Takeyuki Tsuji, Shunta Harada and Tokuyuki Teraji
To compare the map with theory, the researchers fitted the measured fields to the predicted stress pattern. The fit gave a shear modulus of 504 ± 17 gigapascals and a Poisson’s ratio of 0.036 ± 0.033. The reported uncertainty on the Poisson’s ratio is large relative to the fitted value; the authors point out that diamond’s small Poisson’s ratio makes that parameter difficult to determine precisely from this fit.
What a single dislocation map can—and cannot—show
The measurement builds on the team’s earlier work mapping stress around a threading defect, which they concluded was a bundle of dislocations rather than a single one. In the new experiment, identifying one dislocation let the researchers compare the observed field with a specific theoretical case. Their paper argues that precise stress mapping could help researchers study how dislocations contribute to plastic deformation and assess defects in diamond materials.
The result is a validation of the predicted stress pattern for one 45-degree dislocation in diamond—not a demonstration across multiple defect types or materials. Whether the method can recover all six independent tensor components, or preserve similar precision in samples with denser defect networks, remains untested.