Creation of Depth-Confined, Shallow Nitrogen-Vacancy Centers in Diamond With Tunable Density

Engineering shallow nitrogen-vacancy (NV) centers in diamond holds the key to unlocking new advances in nanoscale quantum sensing. We find that the creation of near-surface NVs through delta doping during diamond growth allows for tunable control over both NV depth confinement (with a twofold improvement relative to low-energy ion implantation) and NV density, ultimately resulting in highly-sensitive single defects and ensembles with coherence limited by NV-NV interactions. Additionally, we demonstrate the utility of our shallow delta-doped NVs by imaging magnetism in few-layer CrSBr, a two-dimensional magnet. We anticipate that the control afforded by near-surface delta doping will enable new developments in NV quantum sensing from nanoscale NMR to entanglement-enhanced metrology.

💡 Research Summary

In this work the authors demonstrate a robust method for fabricating shallow nitrogen‑vacancy (NV) centers in diamond with both precise depth confinement and tunable areal density, addressing long‑standing limitations of low‑energy ion implantation. Using plasma‑enhanced chemical vapor deposition (PECVD) they introduce nitrogen in an ultra‑thin “delta‑doped” layer during growth. Two representative samples are produced: Sample A, designed to host individually addressable NVs at a target depth of ~5 nm, and Sample B, engineered to contain a dense NV ensemble at ~10 nm. A conventional 4 keV nitrogen‑ion‑implanted reference (Sample C) is used for comparison.

Depth characterization is performed via 1 H nuclear magnetic resonance (NMR) of a thin oil layer placed on the diamond surface. Sample A exhibits a mean depth of 5.8 nm with a standard deviation of only 1.6 nm, whereas Sample C shows a broader distribution (8.7 nm ± 3.5 nm). This two‑fold improvement in depth uniformity confirms that delta‑doping can place nitrogen atoms with atomic‑scale precision while avoiding the lattice damage typical of implantation.

Coherence properties of single NVs in Sample A are measured with Hahn‑echo and XY8 dynamical decoupling sequences. As expected, T₂ decreases with decreasing depth due to surface‑related magnetic and electric noise, yet the observed T₂ values remain longer than most reported shallow‑NV data. For the shallowest (≈3 nm) NV, the calculated dipole sensitivity (η_dipole) predicts detection of a single surface electron spin with unit signal‑to‑noise in ~100 µs, illustrating the advantage of tighter depth confinement for distance‑dependent sensing.

The high‑density ensemble in Sample B is investigated with XY8 and a more aggressive decoupling protocol called DROID (Dynamic Rephasing of Interacting Dipoles). While XY8 yields T₂ ≈ 27.6 µs, DROID extends the coherence to 75.9 µs—a 2.7‑fold increase—indicating that NV‑NV dipolar interactions, rather than surface noise, dominate the decoherence. This interaction‑limited regime demonstrates that the delta‑doped lattice is sufficiently low‑disorder to allow the intrinsic many‑body dynamics of the NV ensemble to set the coherence ceiling.

To showcase practical utility, the authors place few‑layer CrSBr, a van‑der‑Waals magnet with antiferromagnetic inter‑layer coupling, atop the diamond (encapsulated by a thin SiO₂ film). Using the ensemble sensor they map the stray magnetic field at 80 K. Odd‑layer regions display a finite out‑of‑plane field, while even‑layer regions show near‑zero field, exactly as expected from the known magnetic ordering of CrSBr. The measured field amplitudes agree quantitatively with finite‑element simulations, confirming that the shallow delta‑doped NV ensemble can resolve magnetic textures on the nanometer scale.

The authors discuss broader implications. Precise depth control (≈1 nm) combined with tunable density enables (i) nanoscale NMR of external nuclear spins with enhanced sensitivity, (ii) reporter‑spin based sensing and polarization transfer where uniform coupling is critical, (iii) high‑resolution magnetometry of static and dynamic magnetic textures, and (iv) exploitation of NV‑NV interaction‑limited coherence for entanglement‑enhanced metrology such as spin‑squeezing. They also note that lateral confinement techniques (e.g., focused ion beam or electron‑beam irradiation) can be combined with delta‑doping to create patterned NV arrays for scanning probe devices.

In summary, the paper establishes delta‑doping during PECVD as a scalable, low‑damage route to fabricate shallow NV centers with sub‑nanometer depth spread and controllable areal density. The resulting NVs exhibit coherence limited by intrinsic dipolar interactions rather than surface disorder, delivering superior magnetic‑field and dipole sensitivities. The demonstrated imaging of CrSBr magnetism validates the approach for real‑world quantum‑sensing applications and opens pathways toward advanced quantum metrology, quantum information interfaces, and nanoscale magnetic imaging.