Generation of shallow nitrogen-vacancy centers in diamond with carbon ion implantation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Acta Physica Sinica |
| Authors | Jian He, Yanwei Jia, Ju-Ping Tu, Tian Xia, Xiaohua Zhu |
| Institutions | University of Science and Technology Beijing |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a high-purity, low-energy carbon ion implantation method combined with vacuum annealing to reliably generate shallow Nitrogen-Vacancy (NV) centers in high-nitrogen Ib diamond.
- Core Achievement: Successful creation of shallow NV centers (identified by 575 nm and 637 nm PL peaks) using 180 keV C-ion implantation followed by optimal 950 °C vacuum annealing.
- Method Advantage: Utilizing C-ions avoids introducing foreign impurities, maintaining high chemical purity, and allows the use of lower-cost, high-nitrogen Ib diamond.
- Implantation Damage: C-ion implantation creates a shallow damage layer (simulated depth ~215 nm) characterized by amorphous carbon (91.5% sp2 bonding) and carbon-vacancy cluster defects.
- Mechanism of Formation: The 950 °C annealing process drives solid-phase epitaxy, repairing the crystal lattice (sp2 content drops to 13.6%). Simultaneously, carbon-vacancy clusters dissociate, releasing single vacancies (V).
- NV Center Synthesis: These released single vacancies are captured by native substitutional nitrogen atoms (Ns) present in the Ib diamond, forming the desired NsV quantum defects.
- Defect Analysis: Positron annihilation spectroscopy confirmed the presence of large carbon-vacancy clusters (S parameter = 0.50) in the implanted region, distinct from simple single vacancies.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Substrate Type | Ib (HPHT) | N/A | High-nitrogen single crystal. |
| Initial Nitrogen Concentration | ~100 x 106 | N/A | Calculated from IR absorption (1130 cm-1). |
| Implantation Ion | Carbon (C+) | N/A | Used to create vacancies. |
| Implantation Energy | 180 | keV | Energy of the C-ion beam. |
| Implantation Dose | 5 x 1016 | C+/cm2 | Total implanted dose. |
| Simulated Maximum Range (Rmax) | 284 | nm | SRIM simulation result. |
| Simulated Peak Damage Depth | 215 | nm | Depth of maximum cascade collision. |
| Optimal Annealing Temperature | 950 | °C | Required for full damage recovery and NV formation (Sample S3). |
| Annealing Duration | 2 | h | Time held at annealing temperature (in vacuum). |
| Initial sp2 Content (Post-Implant) | 91.5 | % | XPS result, indicating amorphous carbon layer. |
| Final sp2 Content (950 °C Annealed) | 13.6 | % | XPS result, indicating near-complete crystal recovery. |
| Neutral NV Center PL Peak (NV0) | 575 | nm | Photoluminescence signature. |
| Negative NV Center PL Peak (NV-) | 637 | nm | Photoluminescence signature. |
| Positron S Parameter (Damage Zone) | 0.50 | N/A | Measured at 4-6 keV, indicative of C-vacancy clusters. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment followed a precise sequence of material processing and advanced characterization techniques:
- Substrate Preparation: Commercial Ib single-crystal diamond was mechanically polished on both sides.
- Chemical Cleaning: Samples were cleaned in a hot acid mixture (Nitric acid:Sulfuric acid, 1:4 ratio) at 300 °C to remove surface graphite and metallic contaminants resulting from polishing.
- Carbon Ion Implantation: Implantation was performed using a 400 keV accelerator. Parameters were fixed at 180 keV energy, 5 x 1016 C+/cm2 dose, and vertical incidence.
- Vacuum Annealing: Implanted samples were annealed in a vacuum furnace for 2 hours at three distinct temperatures (850 °C, 900 °C, and 950 °C) to induce defect mobility and lattice repair.
- Raman and Photoluminescence (PL) Spectroscopy: Used a HORIBA system with a 532 nm excitation laser to monitor crystal quality (Raman shift) and NV center formation (PL peaks at 575 nm and 637 nm).
- X-ray Photoelectron Spectroscopy (XPS): Used an ultra-DLD system to analyze the surface bonding state, quantifying the ratio of sp2 (amorphous/graphitic) to sp3 (diamond) carbon bonds.
- Positron Annihilation Spectroscopy (PAS): Employed a mono-energetic slow positron beam (22Na source) to profile vacancy-type defects (carbon-vacancy clusters) as a function of depth (S-E and W-E curves).
Commercial Applications
Section titled âCommercial ApplicationsâThe controlled generation of shallow NV centers is critical for next-generation quantum technologies, particularly those requiring defects close to the diamond surface.
- Quantum Sensing and Magnetometry: Shallow NV centers offer superior sensitivity and spatial resolution for detecting weak magnetic fields (e.g., in biological systems or integrated circuits) compared to bulk NV centers.
- Bio-Imaging and Diagnostics: NV centers are stable, non-photobleaching fluorescent markers suitable for high-resolution bio-labeling and tracking within living cells.
- Solid-State Quantum Devices: The ability to precisely engineer the near-surface defect layer is essential for fabricating quantum registers and spin-based memory elements used in quantum computing prototypes.
- High-Resolution Electric Field Sensing: Shallow NV centers can be used to measure local electric fields with high precision, relevant for microelectronics and materials characterization.
- Diamond Material Engineering: This methodology provides a scalable, high-purity technique for manufacturing specialized quantum-grade diamond substrates, a key component for companies focused on advanced diamond materials.
View Original Abstract
The shallow nitrogen-vacancy center of diamond exhibits excellent sensitivity and resolution in the magnetic detection and quantum sensing areas. Compared with other methods, low-energy carbon ion implantation does not need high-purity diamond nor introduce new impurity atoms, but the formation mechanism of nitrogen-vacancy center is not clear. In this work, shallow nitrogen-vacancy centers are created in the diamond by low energy carbon ion implantation and vacuum annealing, and the transformation mechanism of nitrogen-vacancy centers in diamond is studied by Raman spectroscopy, X-ray photoelectron spectroscopy, and positron annihilation analysis. The results show that shallow nitrogen-vacancy centers can be obtained by carbon ion implantation combined with vacuum annealing. After implantation, superficial layer of diamond shows the damage zone including lattice distortion and amorphous carbon, and carbon-vacancy cluster defects (carbon atoms are surrounded by vacancy clusters) are generated. In the vacuum annealing process, the damaged area gradually transforms into the diamond structure through the recovery of the distortion area and the solid-phase epitaxy of the amorphous carbon area, accompanied by the continuous dissociation of carbon-vacancy cluster defects. When samples are annealed at 850 and 900 â, the structure of the damaged area is partially repaired. While annealing at 950 â, not only the damaged layer is basically recovered, but also nitrogen atoms capture the single vacancy obtained by the dissociation of carbon vacancy clusters, forming the nitrogen-vacancy centers.