The Study of the Efficiency of Nitrogen to Nitrogen‐Vacancy (NV)‐Center Conversion in High‐Nitrogen Content Samples

Abstract

The nitrogen‐vacancy color center in diamond is one of the important systems in the fast‐growing field of sensing. This color center is used in both high‐resolution and high‐sensitivity sensors. However, techniques for the quick and efficient formation of NV centers are still in the development stage. Herein, a study on the influence of the electron irradiation dose on the conversion of substitutional nitrogen into NV− centers is presented. The study is done on diamonds that are highly enriched with nitrogen (≈100 ppm), which, on one hand, should maximize the effect of irradiation, and, on other hand, be of interest for high‐sensitivity magnetometers. The maximum achieved conversion efficiency is as high as 37% ± 3.7%, with no observed saturation on the electron dose even with the simplest annealing procedure. The measurements of the corresponding dephasing time made it possible to make a theoretical estimate for the shot‐noise‐limited magnetic field sensitivity per unit volume of diamond to be roughly ≈ 1 × 10 − 13 T false[ Hz ⋅ mm − 3 false] − 1 .

An Efficient Method to Create High-Density Nitrogen-Vacancy Centers in Cvd Diamond for Sensing Applications

“…NVformation needs three processes: substitutional nitrogen atom, adjutant vacancy, and electron capture. There are two well-established NVcreation methods: (1) implantation of nitrogen ( 14 N or 15 N) ions followed by high-temperature annealing [45], and (2) doping the diamond crystal with N during the growth process and create vacancies by helium ion (He + ) implantation [32,33] or electron irradiation [34,46] followed by subsequent high-temperature annealing. In both methods, the implantation/irradiation of N/He ions creates a high density of vacancies due to the broken bonds/dangling bonds.…”

“…These difficulties lead to poor yield in N-to-NVformation. However, electron irradiation creates broken bonds along with extra electrons, improving NVformation efficiency [34,45].…”

“…To estimate the DC magnetic field sensitivity, we acquired the high-field (|0⬌1⟩) cw-ODMR spectrum at an applied field of 2.3 mT with optimized measurement parameters such as the laser power and MW power (inset of Fig. 3a) [45]. The minimum detected DC magnetic field within the shot noise is given by [14,25,58]:…”

“…We performed Rabi nutation measurements to check the T2,Rabi decay [45] and know the  pulse length required to measure NVspin coherence lifetimes T2 and T1 of the plasma created NVcenters (see below). We applied an MW frequency of 2629 MHz at the |0⬌ − 1⟩ peak along [111] orientation (the left ODMR peak in Fig.…”

“…Nevertheless, the final concentration of NVs still depends on many factors like annealing temperature, cleaning procedures, substrate characteristics, and the N to NVconversion yield (typically <10%) [34]. Recently, progress was made to increase the production yield by more than 30% by optimizing the process (e.g., the electron irradiation dose) [35]. However, >70% of the implanted/doped nitrogen atoms are present in the substrate as substitutional nitrogen, known as P1 paramagnetic centers [36,37] or neutral nitrogen-vacancy (NV 0 ) centers [1].…”