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Researchers at University of Tsukuba have successfully measured electric fields near the surfaces of two-dimensional layered materials with femtosecond temporal and nanometer spatial resolution. They employed a diamond containing a nitrogen-vacancy center—a lattice defect—as a probe within an atomic force microscope, enabling atomic-scale spatial precision.

When nitrogen is incorporated as an impurity in a diamond crystal, the absence of a neighboring carbon atom forms a nitrogen-vacancy (NV) center. Applying an electric field to diamond containing NV centers modifies its refractive index, a phenomenon known as the electro-optic (EO) effect. Notably, this effect has not been observed in pure diamond alone.

In previous work, the research team used a femtosecond laser to detect lattice vibrations in diamond with high sensitivity by measuring the EO effect in high-purity diamond containing NV centers. These results demonstrated that diamond can act as an ultrafast EO crystal and serve as a probe—termed a diamond NV probe—for measuring electric fields.

For the new study, in Nature Communications, the researchers combined the ultrafast EO effect of diamond NV centers with atomic force microscopy to develop a spatiotemporal microscope capable of measuring local electric field dynamics with femtosecond temporal and nanometer spatial resolution.

Using this approach, they successfully detected electric fields near the surface of a tungsten diselenide (WSe₂) sample—a two-dimensional layered material—with temporal and spatial resolutions better than 100 fs and 500 nm.

Due to the NV center's sensitivity to spin states and thermal fluctuations, this diamond-based probe holds potential not only for electric field detection but also for nanoscale magnetic and thermal sensing.