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arXiv:2606.13961

An integrated ultrahigh vacuum cluster tool for diamond surface science and single nitrogen-vacancy center measurements

Zhiyang Yuan, Sorawis Sangtawesin, Lila V. H. Rodgers, Kalliope Zervas, James J. Allred, Jared Rovny, Patryk Gumann, Nathalie P. de Leon

quant-phcond-mat.mtrl-sciSubmitted Jun 11, 2026• Announced Jun 15, 2026• 0 citations
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Abstract

We present a custom-designed ultrahigh vacuum (UHV) cluster tool developed for studying shallow nitrogen-vacancy (NV) centers in diamond, enabling in situ diamond surface preparation, characterization, and single NV center dynamics measurements within a single connected platform. The system combines a surface science chamber for controlled surface modification and analysis with a cryogenic confocal microscope chamber dedicated to NV spin and optical measurements. This integrated approach enables a direct correlation between diamond surface chemistry and the resulting NV spin and charge properties. The instrument provides a versatile platform for systematic studies of surface-induced decoherence mechanisms and charge dynamics for shallow NV centers, and establishes a pathway toward reproducible surface engineering for quantum sensing applications.

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We present a custom-designed ultrahigh vacuum (UHV) cluster tool developed for studying shallow nitrogen-vacancy (NV) centers in diamond, enabling in situ diamond surface preparation, characterization, and single NV center dynamics measurements within a single connected platform. The system combines a surface science chamber for controlled surface modification and analysis with a cryogenic confocal microscope chamber dedicated to NV spin and optical measurements. This integrated approach enables a direct correlation between diamond surface chemistry and the resulting NV spin and charge properties. The instrument provides a versatile platform for systematic studies of surface-induced decoherence mechanisms and charge dynamics for shallow NV centers, and establishes a pathway toward reproducible surface engineering for quantum sensing applications.
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Control of charge-state stability in near-surface quantum defects is critical for nanoscale sensing, yet remains particularly challenging under ultra-high vacuum (UHV), where surface-induced band bending destabilizes the metrologically relevant charge-state. Here, we present a robust and reproducible approach for stabilizing shallowly implanted (< 10 nm deep) nitrogen-vacancy (NV) centers in near-UHV conditions (P = 3×10−93 \times 10^{-9}3×10−9 mbar) based on dielectric interface engineering. Through measurements on individually addressable NV centers, we demonstrate that a TiO2 coating on the diamond suppresses surface-induced electrostatic fields, yielding a 79% increase n NV- population and a 45% enhancement in NV-spin resonance contrast at room temperature. Coherent control measurements further reveal suppressed charge-state conversion dynamics. These results establish dielectric screening as a powerful and reproducible strategy to engineer charge transition energetics of NV centers in scanning-probe-compatible geometries under extreme conditions.
High spatial resolution quantum sensing of near-surface nitrogen vacancy (NV) centers in diamond has enabled detection of magnetic, electrical, and thermal signals at the nanoscale. At depths of just a few nanometers, NV centers serve as localized quantum probes for external spins or low-dimensional materials, but their proximity to the surface also enhances decoherence caused by fluctuating nuclear spins. While advances in surface engineering have stabilized the charge state of NV centers at depths of tens of nanometers, achieving both ultra-shallow implantation (0.5-2 nm) and long-term spin coherence remains a central challenge. In this work, we show using first-principles modeling that, by exploiting the interaction of surface-induced strain and weak dc magnetic fields, the spin coherence times of 1-nm-deep NV centers can be greatly improved near the spin-phonon-confined regime at room temperature in 12C-rich diamonds. We also demonstrate that this protocol benefits ~ 10-nm-deep NV centers in natural diamond, enabling vector magnetometry at the nanoscale. Shallow NV centers in diamond are advantageous for quantum sensing but suffer from surface magnetic noise. Using first-principles simulations supported by experiments, the authors show that a combination of small magnetic fields and surface strain can significantly enhance spin coherence of 1 nm-deep NV centers.
We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 to 100 nm display long spin coherence times, T2 > 100 μs at d = 5 nm and T2 > 600 μs at d ≥ 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.
Shallow nitrogen-vacancy (NV) centers in diamond are promising nanoscale quantum sensors, yet their coherence is strongly limited by surface-induced noise. Surface adsorbates are widely believed to be a major source of decoherence. Here, we test this assumption by characterizing shallow single NV centers under ultrahigh vacuum (UHV) conditions, where the diamond surface is kept free of adsorbates, and comparing their behavior to ambient conditions. Surprisingly, we observe a ~4x reduction in the Hahn echo coherence time T2 in UHV. By combining Hahn echo measurements in the single-quantum (SQ) and double-quantum (DQ) bases, we separate contributions from different noise sources and find that both electric and magnetic noise are enhanced in UHV. In contrast, T1 measurements reveal an increased DQ T1 in UHV, indicating suppressed electric field noise in the ~100 MHz frequency regime. These results point to a modification of the surface noise spectrum upon adsorbate removal, with different frequency regimes arising from distinct microscopic mechanisms. Specifically, we find that the low frequency noise is consistent with increased surface charge in UHV that can be compensated by surface adsorbates in ambient conditions. Our findings highlight a complex and previously underappreciated role of surface adsorbates in shaping the noise environment of shallow NV centers, with important implications for nanoscale quantum sensing.