Shallow Nitrogen Vacancy Color Centers in Diamond by Ion Implantation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-11 |
| Journal | Advanced Quantum Technologies |
| Authors | G. Speranza, Alessandro Cian, B. Perlingeiro CorrĂȘa, Elena Missale, Andrea Pedrielli |
| Institutions | Fondazione Bruno Kessler, Netherlands Organisation for Applied Scientific Research |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a controlled fabrication method for creating shallow Nitrogen-Vacancy (NV) color centers in diamond, critical for high-sensitivity quantum sensing applications.
- Core Achievement: Successful creation of NV defects concentrated in the first 0-30 nm subsurface layer of pure Chemical Vapor Deposition (CVD) diamond, with peak nitrogen concentration confirmed to be within the first 5 nm.
- Methodology: Broad-beam 30 keV N+ ion implantation was performed through a 100 nm Plasma-Enhanced CVD (PECVD) SiO2 screening layer, which effectively reduced ion penetration depth and suppressed channeling.
- Depth Control: Oblique incidence (45°) implantation (Sample D2) achieved a shallower projected range (Rp < 2.6 nm) compared to near-normal incidence (7°, Rp < 5 nm), as predicted by SRIM simulations.
- Charge State Control: Shallower centers (D2) exhibited a higher NV0/NV- ratio (0.9 ± 0.2), confirming increased charge neutralization due to stronger interaction with surface acceptor states.
- PL Intensity: The near-normal incidence sample (D1) showed significantly higher overall Photoluminescence (PL) intensity (150.2 kcts s-1 average) compared to the shallower D2 sample (16.3 kcts s-1 average).
- Characterization: Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) qualitatively confirmed the surface enrichment of nitrogen.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Electronic Grade Single Crystal | Diamond | N background <5 ppb |
| Screening Layer Thickness | 100 ± 2 | nm | PECVD SiO2 |
| Implantation Energy | 30 | keV | N+ ions |
| Total N+ Fluence | 9.0 x 1014 | ions cm-2 | Applied to SiO2/Diamond |
| Incidence Angle (D1) | 7 | degrees | Near-normal |
| Incidence Angle (D2) | 45 | degrees | Oblique |
| Annealing Conditions | 1000 | °C | 3 hours, 10-6 mbar vacuum |
| Predicted N Peak Concentration (D1) | ~2.0 x 1020 | at cm-3 | At diamond surface |
| Predicted N Projected Range (D2) | 0-2.6 | nm | Shallower distribution |
| Measured N Depth (ARXPS Max) | 3.4 (D1) / 3.15 (D2) | nm | Estimated using Maximum Entropy Method |
| NV- Zero-Phonon Line (ZPL) | ~637 | nm | Charged NV state |
| NV0 Zero-Phonon Line (ZPL) | ~575 | nm | Neutral NV state |
| Average PL Intensity (D1) | 150.2 ± 95.7 | kcts s-1 | Confocal PL map (7° incidence) |
| Average PL Intensity (D2) | 16.3 ± 8.2 | kcts s-1 | Confocal PL map (45° incidence) |
| NV0/NV- Ratio (D2) | 0.9 ± 0.2 | unitless | Higher ratio indicates surface neutralization |
| Graphitic Layer Thickness (D2) | ~6 | Angstrom | Derived from C 1s ARXPS fitting |
Key Methodologies
Section titled âKey MethodologiesâThe experimental process flow combined simulation, deposition, implantation, etching, and thermal activation, followed by multi-modal characterization:
- SRIM Simulation: Used to optimize the combination of 30 keV energy, 100 nm SiO2 thickness, and incidence angles (7° and 45°) to ensure the nitrogen distribution peaked at the diamond surface.
- SiO2 Screening Layer Deposition: A 100 nm SiO2 film was deposited on the diamond surface using PECVD to slow down the N+ ions and prevent channeling effects.
- N+ Ion Implantation: Broad-beam implantation was performed at 30 keV with a fluence of 9.0 x 1014 ions cm-2, utilizing both near-normal (7°) and oblique (45°) incidence angles to modulate penetration depth.
- SiO2 Removal: The screening layer was removed using Hydrofluoric Acid (HF) etching, a process that does not affect the diamond surface polishing.
- Thermal Annealing: Samples were annealed at 1000 °C for three hours in a 10-6 mbar vacuum to promote vacancy migration and subsequent trapping by substitutional nitrogen atoms, forming NV centers.
- Angle-Resolved XPS (ARXPS): Used to analyze surface composition (C, O, N, Si) and chemical states. Varying the take-off angle allowed for depth profiling, confirming nitrogen enrichment in the topmost surface layers (<4 nm sampling depth).
- ToF-SIMS Depth Profiling: Monitored the CN- species profile to confirm the trend of nitrogen concentration decrease within the first 15 nm of the diamond substrate, consistent with SRIM predictions.
- PL Spectroscopy: Confocal Raman/PL (515 nm laser, NA 0.9) was used to confirm the formation of both NV- (637 nm ZPL) and NV0 (575 nm ZPL) centers and to quantify the relative NV0/NV- ratio, indicating charge state stability near the surface.
Commercial Applications
Section titled âCommercial ApplicationsâThe controlled fabrication of shallow NV centers is foundational for next-generation quantum technologies, particularly those requiring high spatial resolution and sensitivity near a surface.
- Quantum Sensing (Nano-NMR): Enabling highly efficient coupling between the NV spin and external nuclear spins, allowing for nanotesla-range magnetic field detection and single-molecule Nuclear Magnetic Resonance (NMR) spectroscopy.
- Solid-State Quantum Computing: Providing precisely localized, spectrally stable qubits (NV- centers) necessary for scalable quantum processors and simulators.
- Nano-Thermometry: Utilizing the spin properties of shallow NV centers for high-resolution temperature mapping in microelectronic and biological systems.
- Quantum Communication: Fabricating NV centers with stable optical transitions (lifetime-limited linewidths) for use as quantum repeaters or memory nodes in quantum networks.
- Advanced Materials Characterization: Serving as a noninvasive, high-resolution magnetic imaging tool (scanning SQUIDs or magnetic force microscopy alternatives) for characterizing novel materials like 2D materials or topological insulators.
- Deterministic Emitter Fabrication: The screening layer technique provides a pathway toward creating isolated, single NV centers by using extremely low fluence recipes, essential for single-photon source applications.
View Original Abstract
Abstract Recent advancements in quantum technologies are fueled by the ability to engineer materials with specific quantum properties, enabling various applications. The nitrogenâvacancy (NV) center in diamond is a key system for nanoscale sensors, capable of detecting weak magnetic fields with nanoteslaârange sensitivity. To achieve high spatial resolution and sensitivity, NV centers must be placed near the diamond surface. This study investigates the creation of NV defects in a pure chemical vapor deposition (CVD) diamond single crystal via broadâbeam ion implantation. The implantations are performed through thin (100 nm) SiO 2 layers deposited by plasmaâenhanced CVD (PECVD). Both normal and oblique ion beam incidences are used, with the oblique incidence chosen to reduce the nitrogen ion penetration depth. Simulations show a subsurface NV center distribution, with the highest concentration near the surface; the expected trends are confirmed by angleâresolved Xâray photoelectron spectroscopy (ARXPS) and timeâofâflight secondary ion mass spectrometry (ToFâSIMS). This distribution extends to a depth of 30 nm. By adjusting the ion beam incidence angle, NV center density can be modulated. This work contributes to optimizing the fabrication process for shallow color centers through ion implantation using a screening layer.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2013 - Second Edition, Spin Dynamics: Basics of Nuclear Magnetic Resonance