Femtosecond laser writing of preferentially orientated shallow NV centers in (111) diamond

Nitrogen-vacancy (NV) centers in diamond are highly stable quantum emitters, demonstrating significant potential applications in quantum sensing. The performance of NV centers as quantum sensors is fundamentally constrained by their depth in diamond and orientation, since shallow NV centers exhibit higher detection sensitivity owning to depth-dependent photon collection efficiency, and high alignment ratio of NV center orientation can improve the sensing contrast in spin-state readout. However, the current mainstream preparation methods for NV centers still face significant challenges in simultaneously manipulating the depth and orientation of NV centers. This study achieved the preparation of shallow-oriented single NV centers on the (111) diamond coated with a boron nitride (BN) film using linearly polarized femtosecond laser irradiation. By utilizing high-energy focused laser-induced ions ionized from BN film by Coulomb explosion collide with the diamond to generate vacancies near the diamond surface followed by subsequent thermal annealing, NV centers within a 100-nm depth range below the diamond surface was fabricated under room temperature conditions, and the yield of single NV centers was up to 88.5%. The optically detected magnetic resonance spectral analysis revealed that NV centers exhibited a preferential orientation along the [111] direction, with an orientation ratio of 60% significantly higher than the natural orientation distribution of NV centers. This method combines high spatial resolution, controllable orientation, and room-temperature processing advantages, providing a new technical pathway for the development of high-performance quantum sensors.