Negatively charged nitrogen-vacancy centers in a 5 nm Thin ¹²C diamond film

We report successful introduction of negatively charged nitrogen-vacancy (NV^-) centers in a 5 nm thin, isotopically enriched ([¹²C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NV^- in such a thin layer even when the surface is terminated by hydrogen atoms. NV^- centers are found to have spin coherence times of between T₂ ∼ 10-100 μs at room temperature. Changing the surface termination to oxygen or fluorine leads to a slight increase in the NV^- density, but not to any significant change in T₂. The minimum detectable magnetic field estimated by this T₂ is 3 nT after 100 s of averaging, which would be sufficient for the detection of nuclear magnetic fields exerted by a single proton. We demonstrate the suitability for nanoscale NMR by measuring the fluctuating field from ∼10⁴ proton nuclei placed on top of the 5 nm diamond film.