The influence of methane concentration during chemical vapor deposition of diamond on the formation of needle-like crystallites with nitrogen vacancy centers

A comparative study of the photoluminescent and cathodoluminescent characteristics of color centers in diamond needle-like crystallites was conducted. The diamond needles were extracted from polycrystalline films deposited from a direct current discharge-activated gas mixture of methane and hydrogen. During the growth of the diamond films, the methane concentration in the gas mixture was varied from 0.5% to 3.5%. The study revealed a significant influence of the methane concentration on the concentration and charge state of nitrogen-vacancy (NV) centers formed within the diamond needles. It was found that while the total concentration of NV centers decreases with increasing methane content, the relative fractions of the negatively charged NV(-) and neutral NV(0) centers exhibit a non-monotonic dependence. A local maximum in the concentration of NV(-) centers and the minimum for NV(0) centers were observed at a methane concentration of 1.5%. The results obtained can be used to optimize the luminescent characteristics of diamond needles for practical use in quantum optical devices.