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

This study examined how pulsed nitrogen gas flow affects the microstructure and nitrogen-vacancy (NV) center formation in polycrystalline diamond films grown by microwave plasma chemical vapor deposition. Compared to continuous nitrogen flow, pulsed flow allowed better control of nitrogen-related radicals and caused the diamond structure to change from microcrystalline to nanocrystalline, along with changes in residual stress and NV emission properties. With optimized pulsed nitrogen conditions, a bimodal structure was formed, consisting of (001)-oriented, flake-like microcrystalline grains embedded within a nanocrystalline diamond matrix. Confocal optical measurements showed that negatively charged NV (NV-) centers were mainly located in highly crystalline grains, while neutral NV (NV0) centers were concentrated at grain boundaries, creating spatially separated NV-rich clusters. Relaxometry results indicated that the longitudinal relaxation times of the flake-like grains were comparable to those of high-quality single-crystal diamond. Overall, the results demonstrate that pulsed nitrogen flow is an effective method for controlling diamond microstructure and improving NV center formation, highlighting its strong potential for quantum technology applications.