Defect evolution in nitrogen-implanted CVD diamond during thermal annealing: The formation of NV centers and vacancy clusters

We investigate the thermal evolution of implantation-induced defects in single-crystal CVD diamond using depth-resolved positron annihilation lifetime spectroscopy (PALS). Samples were implanted with ions at a fluence of and annealed between and . By varying the positron implantation energy, we probe defect populations as a function of depth and quantify their types and concentrations. In the pristine material, small vacancies, predominantly divacancies, are detected at ppm levels together with a low concentration of larger vacancy clusters. Nitrogen implantation increases the abundance of mono-/divacancies. In nitrogen-rich regions, fewer isolated vacancies are observed despite higher displacement damage. Upon annealing, small vacancies become mobile. In nitrogen-poor regions they agglomerate and grow pre-existing clusters, whereas in nitrogen-rich zones they are efficiently captured by substitutional nitrogen to form NV centers, which limits the formation of new vacancy clusters. At annealing above , positron annihilation occurs predominantly in perfect bulk or small open-volume defects consistent with NV center-related positron lifetimes. These results reveal a nitrogen content- and temperature-dependent competition between vacancy clustering and NV center formation. • Detection of mono- and divacancies in as-received CVD diamond. • Detection of large vacancy clusters of more than 40 missing carbon atoms. • Verification that divacancies represent the most stable type of defect in diamond. • Characterization of the defect landscape during the fabrication process of NV centers. • Description of the method, serving as a reference for studying vacancy-related quantum systems.