Quantifying selective alignment of ensemble nitrogen-vacancy centers in (111) diamond

Selective alignment of nitrogen-vacancy (NV) centers in diamond is an important technique towards its applications. Quantification of the alignment ratio is necessary to design the optimized diamond samples. However, this is not a straightforward problem for dense ensemble of the NV centers. We estimate the alignment ratio of ensemble NV centers along the [111] direction in (111) diamond by optically detected magnetic resonance measurements. Diamond films deposited by N₂ doped chemical vapor deposition have NV center densities over 1 × 10¹⁵cm⁻³ and alignment ratios over 75%. Although spin coherence time (T₂) is limited to a few μs by electron spins of nitrogen impurities, the combination of the selective alignment and the high density can be a possible way to optimize NV-containing diamond samples for the sensing applications.