Photoactivation of NV Centers in Diamond via Continuous Wave Laser Illumination of Shallow As‐Implanted Nitrogen
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-05-02 |
| Journal | Advanced Functional Materials |
| Authors | Jens Fuhrmann, Christoph Findler, Michael Olney‐Fraser, Lev Kazak, Fedor Jelezko |
| Institutions | Center for Integrated Quantum Science and Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research introduces a novel, scalable method for creating negatively charged Nitrogen-Vacancy (NV-) centers in diamond using continuous-wave (cw) blue laser photoactivation, entirely bypassing traditional high-temperature thermal annealing.
- Non-Thermal Activation: NV- centers are locally activated in shallow 5 keV 15N+ implanted diamond using a 405 nm cw laser, with estimated local temperature increases remaining low (~114 °C).
- High Coherence: The resulting single NV- centers exhibit long Hahn echo T2 coherence times, reaching up to 331 ± 30 µs, comparable to centers created via conventional high-temperature annealing.
- Competitive Yield: For the lowest implantation dose (1 x 109 15N+ cm-2), the NV- creation yield is estimated at 6 ± 3 %, matching state-of-the-art thermal annealing results for shallow implants.
- Charge Stability: The photoactivated NV- centers demonstrate long-term charge stability, showing no blinking behavior or bleaching over 104 days of observation.
- Localized Control: The activation is confined to the laser focal spot, enabling precise, in-situ, and targeted creation of single or ensemble NV- centers within pre-fabricated photonic structures.
- Mechanism: Activation appears to be governed by a one-photon process related to charge dynamics (ionization of adjacent defects), rather than thermal vacancy diffusion.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Substrate | Type IIa, (100) face | N/A | Electronic-grade single crystal |
| Implantation Ion | 15N+ | N/A | Used for nuclear spin confirmation |
| Implantation Energy | 5 | keV | Shallow implantation |
| NV Median Depth (Measured) | 12 ± 4 | nm | Corresponds to ~15 nm C-TRIM estimate |
| Implantation Dose Range | 1 x 109 to 1 x 1016 | 15N+ cm-2 | Tested range |
| Activation Wavelength | 405 (or 375) | nm | Continuous-wave (cw) laser |
| Activation Power Range | 50 to 1300 | µW | Measured at objective |
| PL Saturation Power (405 nm) | 400 to 800 | µW | Threshold for fluorescence saturation |
| Activation Energy (Saturation Es) | 0.5 ± 0.1 | J | Total energy delivered for half activation |
| Estimated Surface Temperature | ~114 | °C | Max T increase during 1300 µW, 32 min activation |
| NV- Creation Yield (Min Dose) | 6 ± 3 | % | For 1 x 109 15N+ cm-2 dose |
| Hahn Echo T2 (Maximum) | 331 ± 30 | µs | Measured for single NV- centers (lowest dose) |
| Hahn Echo T2 (Median) | 49 ± 42 | µs | Measured for single NV- centers (lowest dose) |
| Rabi Read-Out Contrast | 34 ± 3 | % | Good charge state stability (lowest dose) |
| 15N Nuclear Splitting | ~3.1 | MHz | Confirms activation of implanted 15N species |
Key Methodologies
Section titled “Key Methodologies”The NV- center creation process involves three primary stages: cleaning, ion implantation, and optical photoactivation, followed by characterization.
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Sample Cleaning (Pre- and Post-Implantation):
- The diamond surface was cleaned using a boiling 1:1:1 triacid mixture (Sulfuric acid, Perchloric acid, Nitric acid).
- Process parameters: 170 °C for 30 min, resulting in an oxygen-terminated diamond surface.
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Ion Implantation:
- A gas-source ion implantation system was used with 98% enriched 15N2 gas.
- Ions: Atomic 15N+ species.
- Energy: 5 keV, resulting in shallow implantation (median depth ~12 nm).
- Doses: Logarithmically spaced spots ranging from 1 x 109 to 1 x 1016 15N+ cm-2.
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Photoactivation (Non-Thermal):
- A home-built confocal microscope was used for activation.
- Laser Source: Continuous-wave (cw) 405 nm laser diode (375 nm was also tested for comparison).
- Illumination Parameters: Power varied from 50 µW up to 1300 µW; illumination time up to 32 min per spot.
- Activation Method: Localized illumination within the focal spot (NA = 0.95 objective), sometimes combined with lateral scanning (e.g., 6 x 6 µm2 area).
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Characterization:
- PL Measurement: 532 nm cw laser (300 µW) used to probe NV concentration and fluorescence saturation behavior.
- Single Emitter Confirmation: Second-order correlation measurement (g(2)(τ)) showing anti-bunching (g(2)(0) less than 0.5).
- Coherence Measurement: Pulsed optically detected magnetic resonance (ODMR) using a 532 nm excitation laser and microwave pulses (B ≈ 500 G external magnetic field) to determine T1, Ramsey T2*, and Hahn echo T2 times.
Commercial Applications
Section titled “Commercial Applications”The ability to create stable, high-coherence NV- centers locally without high-temperature annealing is crucial for integrating quantum emitters into complex, pre-fabricated devices.
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Quantum Sensing and Metrology:
- Room Temperature Operation: NV- centers are ideal for high-sensitivity magnetic, electric field, strain, and temperature sensing protocols at ambient conditions.
- Shallow Emitters: The 12 nm depth is optimal for sensing external signals (e.g., biological samples, material surfaces).
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Integrated Quantum Photonics:
- Targeted Integration: Enables deterministic placement of NV- centers into pre-fabricated photonic nanostructures (e.g., cavities, waveguides) for enhanced light collection and quantum networking.
- Time Efficiency: Bypasses the lengthy and energy-intensive thermal annealing step, accelerating device fabrication cycles.
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Hybrid Device Manufacturing:
- Temperature-Sensitive Components: Allows NV- activation after the integration of temperature-sensitive materials (e.g., gold microwave structures, metal electrodes, or semiconductor layers) that would be damaged by 1000 °C annealing.
- Charge Environment Engineering: The photoactivation mechanism, relying on charge dynamics, offers a pathway for optimizing the local charge environment around the NV center post-implantation.
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Scalable Fabrication:
- The use of readily available cw laser diodes and confocal microscopy makes the activation process simple, cost-effective, and potentially scalable for localized processing.
View Original Abstract
Abstract Negatively charged nitrogen‐vacancy (NV − ) centers in diamond are appealing for quantum sensing applications due to their environmental sensitivity and long coherence times. Precise and scalable shallow color center creation is essential yet challenging for technological quantum applications. This is due to the involvement of several lengthy processes, such as ion implantation and thermal annealing of the samples. The latter process can be addressed by application of an alternative activation technique that bypasses the high‐temperature annealing. For this, nitrogen‐implanted regions on a diamond substrate are exposed to continuous‐wave 405 nm laser radiation. The illumination leads to local activation of NV − centers with photoluminescence yield saturation for regions activated with laser power at around 800 µW. For low implantation doses, single NV − centers are created with corresponding mean T 2 coherence time value around 71 µs. The NV − creation yield for the lower implantation doses match conventional creation methods, while higher doses show reduced yield values. However, the coherent properties are comparable to NV − centers within annealed samples. This shows that the activated NV − centers are well‐suited for advanced applications in quantum sensing and related technologies.