Fig. 1. Fundamental principle. (a) The crystal structure of the NV center; (b) the spin levels in the ground state of the NV center; (c) the optically detected magnetic resonance spectra of NV center under conditions with and without an external magnetic field, the upper blue curve has been properly vertically shifted; (d)schematic diagram of a diamond probe

Fig. 2. ODMR module. (a) The design of confocal optical path; (b) schematic diagram of timing synchronization and control process

Fig. 3. Scanning imaging module. (a) The diamond probe structure; (b) SEM image of the probe substrate; (c) SEM image of a single pillar; (d) schematic diagram of the scanning imaging system

Fig. 4. The structures of the samples. (a) Optical microscope image of the samples, where the red arrow indicates the location of the sample; (b) AFM images of two samples

Fig. 5. The results of the measurement. (a) MFM results of samples with different thicknesses, the scale is 5 μm; (b) the scanning NV test results of samples with different thicknesses, and the scanning area corresponds to the area shown in the blue dashed box in Fig. 5(a), the scale is 1 μm