Formation of nitrogen-vacancy centers in (001)-textured polycrystalline diamond layers through pulsed nitrogen gas flow

The influence of pulsed nitrogen gas flow on microstructure and nitrogen-vacancy (NV) center formation was systematically investigated in polycrystalline diamond layers synthesized by microwave plasma chemical vapor deposition. Compared with static flow, gas pulsing enabled precise control of nitrogen-related radicals and induced a transition from microcrystalline to nanocrystalline diamond, accompanied by variations in residual stress and NV emission. Under optimized nitrogen flow, a bimodal structure emerged, comprising (001)-oriented, flake-like microcrystalline grains embedded in nanocrystalline diamond. Confocal optical analysis revealed that negatively charged NV (NV − ) centers were preferentially localized within highly crystalline grains, whereas neutral NV (NV 0 ) centers predominated at grain boundaries, forming spatially separated NV − -rich clusters. Relaxometry demonstrated that the longitudinal relaxation times of flake-like grains were comparable to those of high-quality single-crystal diamond. These findings demonstrate that pulsed nitrogen modulation provides an effective strategy for tailoring diamond microstructure and optimizing NV center formation, offering significant potential for quantum applications.