Diamond anvil cells have made it possible for scientists to recreate extreme phenomena, such as the crushing pressures deep inside the Earth’s mantle, or to enable chemical reactions that can only be triggered by intense pressure, all within the confines of a laboratory apparatus. To develop new, high-performance materials, scientists need to understand how useful properties, such as magnetism and strength, change under such harsh conditions. But often, measuring these properties with enough sensitivity requires a sensor that can withstand the crushing forces inside a diamond anvil cell. By turning natural atomic flaws inside the diamond anvils into tiny quantum sensors, scientists have developed a tool that opens the door to a wide range of experiments inaccessible to conventional sensors.
At the atomic level, diamonds owe their sturdiness to carbon atoms bound together in a tetrahedral crystal structure. But when diamonds form, some carbon atoms can get bumped out of their “lattice site,” a space in the crystal structure that is like their assigned parking spot. When a nitrogen atom impurity trapped in the crystal sits adjacent to an empty site, a special atomic defect forms: a nitrogen-vacancy (NV) center. Scientists have used NV centers as tiny sensors to measure the magnetism of a single protein, the electric field from a single electron, and the temperature inside a living cell.
To take advantage of the NV centers’ intrinsic sensing properties, researchers engineered a thin layer of them directly inside the diamond anvil in order to take a snapshot of the physics within the high-pressure chamber. After generating a layer of NV center sensors a few hundred atoms in thickness inside one-tenth-carat diamonds, the researchers tested the NV sensors’ ability to measure the diamond anvil cell’s high-pressure chamber.
The sensors glow a brilliant shade of red when excited with laser light. By probing the brightness of this fluorescence, the researchers were able to see how the sensors responded to small changes in their environment. The NV sensors suggested that the once-flat surface of the diamond anvil began to curve in the center under pressure — a phenomenon called “cupping,” a concentration of the pressure toward the center of the anvil tips.
Now that they’ve demonstrated how to engineer NV centers into diamond anvil cells, the researchers plan to use the device to explore the magnetic behavior of superconducting hydrides — materials that conduct electricity without loss near room temperature at high pressure, which could revolutionize how energy is stored and transferred.