Formation of Nitrogen-Vacancy (NV) Centers in Diamond by Ultrafast Laser Irradiation and Quantification of Nitrogen Concentration

Nitrogen (N) is a common impurity in both natural and synthetic diamonds and is extensively studied as the presence of nitrogen influences the diamond’s electronic and optical properties. Determining nitrogen concentration is essential for the development and optimization of diamond-based devices, and it also offers important insights into the nitrogen doping profile variations across the diamond sample. A traditional technique for determining nitrogen concentration inside a diamond is Secondary Ion Mass Spectrometry (SIMS) analysis, which requires ultra-high vacuum conditions and provides more knowledge on depth distribution but has limited spatial resolution due to the primary beam diameter. Cathodoluminescence, by comparison, has a poor depth resolution of a few tens of nanometer (nm). This work explores the potential of nitrogen-vacancy (NV) centers for quantifying nitrogen concentration within diamond samples.<br/>Diamonds with NV centers consisting of a substitutional nitrogen atom and an adjacent vacancy are being considered as registers for a qubit state, as quantum sensors, and as a possible component in hybrid quantum information processing for their excellent room temperature electron spin properties as well as their capability as single photon emitters. Since the formation and number of NV centers correlate directly with the amount of nitrogen within the diamond lattice, presenting a unique opportunity to use the number of created NV centers to map nitrogen concentration with exceptional spatial resolution.<br/>An effective method to create vacancies and eventually NV centers at deterministic positions with high spatial precision is provided by laser writing that utilizes a highly focused laser spot to displace carbon atoms from the lattice in a diamond. The number of vacancies generated by this method can be effectively controlled by adjusting the laser parameters. Here, we demonstrate the creation of NV centers in nitrogen-doped diamonds at predetermined positions through femtosecond laser irradiation. Since the laser-generated heat is used for annealing, the NV centers are formed within the laser beam focal spot. To resolve NV centers in diamonds with sub-50 nm spatial resolution, Stimulated Emission Depletion (STED) microscopy, a super-resolution microscopy technique that breaks the diffraction limit of the light is being built. The intensity of NV centers is directly linked with the number of NV centers created and, consequently, the concentration of nitrogen present in the diamond material, which offers a promising approach to map the distribution of nitrogen within the laser written area. This method provides a non-destructive, simplified process for quantifying nitrogen concentration at the nanoscale range within diamond samples. We are using this technique to study selective area growth of diamond and initial results will be reported.