Shallow nitrogen-vacancy (NV) centers in diamond are useful for near-surface sensing, but the negatively charged state ${\mathrm{NV}}^{-}$ is often difficult to stabilize close to the surface. Here we study the depth dependence of NV formation and charge-state stability in nitrogen-implanted diamond using spatially resolved photoluminescence (PL) spectroscopy, dynamic secondary ion mass spectrometry (D-SIMS), stopping and range of ions in matter (SRIM) simulations, and first-principles density functional theory (DFT) calculations. Although the near-surface region contains a higher nitrogen concentration, its NV-related PL emission is much weaker than that from the shallow subsurface region. This behavior shows that nitrogen incorporation alone is not sufficient to explain the observed ${\mathrm{NV}}^{-}$ stability. The depth profiles obtained from D-SIMS and SRIM support the intended difference between the near-surface and shallow-subsurface implantation regions. To examine the possible role of residual implantation damage, we further compare ideal NV and carbon-interstitial-related NV (NV-int) defect models by DFT. The interstitial-related defect model gives an upward shift of the $\varepsilon \left(0/-\right)$ transition level by about 3.23 eV. Charge-density-difference and density-of-states analyses further reveal local charge redistribution and reconstruction of defect-related electronic states around the NV center. These changes establish a microscopic explanation for the reduced stability of ${\mathrm{NV}}^{-}$ in defect-rich near-surface regions. Our results indicate that shallow NV engineering should focus not only on nitrogen placement, but also on reducing residual implantation-induced defects.

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• Defects
• Nitrogen vacancy centers in diamond