Pressure is a fundamental parameter that changes the properties of matter: oxygen becomes a metal, hydrides become superconductors. A diamond anvil cell (a device with two diamonds squeezing a sample) generates hundreds of gigapascals, but pressure is unevenly distributed inside the chamber. Classical methods, such as ruby fluorescence or diffraction, give a value at a point or an averaged picture. This work sits alongside studies that have already used nanodiamonds as sensors for magnetic fields and temperature in diamond anvil cells, but here, for the first time, a pressure map is constructed across the entire chamber volume.
Nanodiamonds 50 nm in size with nitrogen-vacancy centers, along with ruby for calibration and an iron sample, were placed in a diamond anvil cell with a culet diameter of 260 μm. Sodium chloride served as the pressure-transmitting medium. Two packing configurations were used: in one, the nanodiamonds lay directly on the diamond; in the other, they were covered with a salt layer on top. The sample was irradiated with a green laser (532 nm) and microwaves, and red fluorescence was recorded with a CMOS camera. For each point in the chamber, an optically detected magnetic resonance spectrum was obtained and fitted with models of hydrostatic or uniaxial compression.
In the single-salt-layer configuration (nanodiamonds touching the diamond), the spectra were asymmetric. The uniaxial compression model gave an axial pressure of 22.1 GPa and a transverse pressure of 12.5 GPa, corresponding to an anisotropy of 1.77. Across the chamber, axial pressure varied from 14 to 30 GPa, transverse pressure from 10 to 20 GPa, and the pressure ratio dropped from 1.6–1.8 at the center to 1.4 at the edges. In the two-salt-layer configuration, the spectra were symmetric, and the hydrostatic model gave a pressure of 17–20 GPa, consistent with the ruby calibration (20.0 GPa). The anisotropy in this case was 1.2–1.5, noticeably lower.
This work demonstrates that nanodiamonds can serve as distributed pressure sensors with micron resolution inside a diamond anvil cell. Unlike neighboring studies, where nanodiamonds were mainly used to measure magnetic fields or temperature, here a complete map of non-hydrostaticity in the chamber at 20 GPa is obtained for the first time. The method requires no complex optics and is compatible with wide-field microscopy, making it fast and convenient for routine experiments.
The technique can be extended to simultaneous measurement of pressure, temperature, and magnetic field in a single chamber. It may also be possible to use nanodiamonds of different sizes or orientations to improve accuracy. In the future, the method could be applied to studying phase transitions and superconductivity under pressure, where local uniformity of compression is important.
The method will be useful in high-pressure physics, materials science, and geophysics, where controlling the compression conditions of a sample is essential. It could also accelerate the search for new superconductors by allowing quick checks of hydrostaticity in the chamber.
The next step is to calibrate the method at higher pressures (up to 100 GPa) and test it with other pressure-transmitting media. The influence of nanodiamond size and concentration on map accuracy should also be investigated.
In high-pressure physics, an open question remains: how does non-hydrostaticity affect measurements of material properties? This work provides a tool for quantifying that non-hydrostaticity, which could help interpret experiments on superconductivity and phase transitions.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This work demonstrates the use of nanodiamonds with NV centers to map pressure distribution in a diamond anvil cell at approximately 20 GPa. Two sample loading configurations are compared: one with a single NaCl layer and another with two NaCl layers, showing that the latter provides more hydrostatic conditions. Micron-scale maps of axial and transverse pressure were obtained, revealing anisotropy.
Where its strength is
For the first time, a complete map of non-hydrostaticity inside a high-pressure chamber has been obtained with micron resolution, using wide-field optics and a CMOS camera, making the method fast and suitable for routine experiments.
Where it could go next
Worth trying
Why this may matter
The method could become a standard tool for monitoring conditions in high-pressure experiments, especially in studies of superconductivity and phase transitions, where pressure homogeneity is crucial.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.55, against a usual 0.64. It looks like few have drilled nearby.
Nanodiamonds 50 nm in size are so small that about 8 trillion of them fit in a single cubic millimeter. At 20 GPa, the distance between atoms in diamond decreases by about 1.5%, yet the nitrogen-vacancy center remains stable and continues to glow.