Perfectly aligned shallow ensemble nitrogen-vacancy centers in (111) diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-07-24 |
| Journal | Applied Physics Letters |
| Authors | Hitoshi Ishiwata, Makoto Nakajima, Kosuke Tahara, Hayato Ozawa, Takayuki Iwasaki |
| Institutions | Tokyo Institute of Technology |
| Citations | 56 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation for 6CCVD
Section titled âTechnical Analysis and Documentation for 6CCVDâExecutive Summary
Section titled âExecutive SummaryâThis study demonstrates a critical advancement in quantum material engineering, utilizing step-flow Microwave Plasma Chemical Vapor Deposition (MPCVD) to produce perfectly aligned, high-density, shallow Nitrogen-Vacancy (NV) center ensembles on (111) diamond. This material platform is immediately applicable to high-sensitivity quantum magnetometry and nanoscale nuclear magnetic resonance (NMR).
- Perfect Alignment: Achieved greater than 99% alignment of NV centers along the [111] crystal direction, confirmed by Optically Detected Magnetic Resonance (ODMR).
- Shallow and Precise Depth: NV centers were confined to a precise depth of 9-10.7 nm from the surface, with an error margin of less than ±0.8 nm, suitable for surface-sensitive detection.
- High Ensemble Density: NV concentration reached $6.1 \times 10^{15}$ to $3.1 \times 10^{16}$ cm-3, overcoming the low density limitations of previous CVD methods.
- High Coherence/Contrast: The aligned ensembles demonstrated a high Rabi contrast (approximately 30%), comparable to single NV center experiments, while maintaining a T2 coherence time of up to 6 ”s.
- Methodology Validation: Step-flow growth on off-angle (111) substrates, combined with a high N:C ratio (>6.4), proved effective for atomic-level control of nitrogen incorporation and alignment.
- Application Ready: The resultant material enables surface-sensitive nanoscale NMR detection of nuclear spins (Proton 1H and Fluorine 19F), pioneering large-area quantum magnetometry.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context / Measurement |
|---|---|---|---|
| Substrate Orientation | (111) IIa | N/A | Essential for step-flow alignment |
| Substrate Off-Angle | 2 - 3 | ° | Along the <1Ì1Ì2> direction |
| NV Center Alignment Ratio | >99 | % | Confirmed via CW-ODMR spectrum |
| NV Center Depth (Shallow) | 9 - 10.7 (±0.8) | nm | Nanoscale NMR (XY8-80 sequence) and SIMS |
| Ensemble NV Concentration | 6.1 x 1015 to 3.1 x 1016 | cm-3 | Calculated from confocal photon counts |
| Nitrogen Delta Doping Density | >1019 | cm-3 | SIMS measurement of the doping layer |
| Spin Coherence Time (T2) | 6 | ”s | Hahn Echo measurement (at 3.2 sccm N2 flow) |
| Rabi Oscillation Contrast | ~30 | % | Observed on perfectly aligned NV ensembles |
| CVD Growth Pressure | 75 | Torr | MPCVD conditions |
| CVD Growth Temperature | 900 | °C | MPCVD conditions |
| Growth Rate (Doping Layer) | 0.29 - 0.3 | nm s-1 | Determined by SIMS thickness profile |
| N2 Flow Rate (Doping) | 3.2 - 4 | sccm | Key parameter for controlling density and T2 |
| N:C Ratio (High) | 8 - 6.4 | N/A | High ratio used to induce high N incorporation |
Key Methodologies
Section titled âKey MethodologiesâThe perfect alignment and shallow depth control of NV ensembles were achieved through highly specific step-flow MPCVD parameters:
- Substrate Preparation: Utilized high-purity Diamond IIa (111) substrates with a controlled off-angle corresponding to 2-3° along the <1Ì1Ì2> direction. This off-angle is critical for enabling lateral step-flow growth.
- Intrinsic Layer Growth: A thick intrinsic diamond layer was grown for 7 hours using MPCVD prior to NV formation to ensure a high-quality bulk material and low background nitrogen concentration (< 5 x 1016 cm-3).
- Shallow Delta Doping: NV centers were formed via a short, precise doping pulse (30-120 seconds) of nitrogen during step-flow growth, targeting a growth rate of 0.29-0.3 nm s-1.
- Optimized Gas Recipe: Growth conditions included 75 Torr pressure, 620 W power, and 900 °C temperature, with a total flow of 1000 sccm.
- Methane (CH4) flow: 0.5 sccm.
- Nitrogen (N2) flow: 3.2-4 sccm (resulting in an effective N:C ratio of 8-6.4).
- Hydrogen (H2) acted as the carrier gas.
- Alignment Mechanism: The combination of the (111) orientation and the step-flow growth kinetics ensures that nitrogen incorporation occurs preferentially at step edges, resulting in the desired NV axis alignment (more than 99%).
- Characterization: The resulting films were rigorously characterized using SIMS (depth/concentration), AFM (surface morphology/step height), and ODMR/Rabi/Hahn echo measurements (alignment, contrast, and T2 coherence).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis breakthrough research highlights the critical importance of ultra-high quality, precisely engineered diamond substrates for advancing quantum sensing. 6CCVD specializes in the materials required to replicate and scale this methodology, offering full material customization and engineering support.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the perfect alignment achieved via step-flow epitaxy, researchers require substrates with stringent crystallographic specifications.
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Optical Grade Single Crystal Diamond (SCD): Required Material. 6CCVD supplies ultra-pure, low-strain SCD wafers. Specifically, for this application, researchers need:
- (111) Orientation: Absolute necessity for replicating the NV alignment demonstrated in the paper.
- High Purity (IIa Equivalent): Essential for maintaining a long spin coherence time (T2) by minimizing background impurities.
- Thickness: SCD Substrates up to 10 mm are available, providing robust handles for subsequent MPCVD re-growth and processing.
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Customization Potential:
- Precision Substrate Off-Angle Engineering: The paper relies on a specific 2-3° off-angle along the <1Ì1Ì2> direction to induce the necessary step-flow growth. 6CCVD offers custom-oriented SCD wafers with tight angular tolerance specifications to optimize step density and NV alignment.
- Ultra-Polished Surfaces: The quality of the surface preparation impacts step-flow. 6CCVD guarantees SCD polishing to a surface roughness of Ra < 1 nm, critical for atomic-scale epitaxial control.
- Controlled Doping & Re-growth: Our MPCVD capability allows for precise ultra-thin film deposition and delta doping layers, providing the atomic-level control required to embed NV centers 9-10 nm from the surface.
- Integrated Device Features (Metalization): Quantum magnetometry devices frequently require integrated microwave transmission lines (striplines) for coherent manipulation. 6CCVD offers full in-house metalization services including Au, Pt, Ti, and Pd deposition, enabling rapid prototyping of functional quantum sensors on the newly grown NV layers.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team can assist with material selection for similar quantum magnetometry and nanoscale NMR projects, providing expertise in:
- Optimizing substrate off-angle specifications for specific step-flow kinetics.
- Designing precise CVD recipes for shallow, high-density delta-doping layers.
- Balancing high nitrogen concentration (for stable NV- formation) against P1 center formation (which limits T2 coherence time).
- Post-growth processing, including custom etching and metalization for device integration.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).
View Original Abstract
We report the formation of perfectly aligned, high-density, shallow nitrogen vacancy (NV) centers on the (111) surface of a diamond. The study involved step-flow growth with a high flux of nitrogen during chemical vapor deposition (CVD) growth, which resulted in the formation of a highly concentrated (&gt;1019 cmâ3) nitrogen layer approximately 10 nm away from the substrate surface. Photon counts obtained from the NV centers indicated the presence of 6.1 Ă 1015-3.1 Ă 1016 cmâ3 NV centers, which suggested the formation of an ensemble of NV centers. The optically detected magnetic resonance (ODMR) spectrum confirmed perfect alignment (more than 99%) for all the samples fabricated by step-flow growth via CVD. Perfectly aligned shallow ensemble NV centers indicated a high Rabi contrast of approximately 30% which is comparable to the values reported for a single NV center. Nanoscale nuclear magnetic resonance demonstrated surface-sensitive nuclear spin detection and provided a confirmation of the NV centersâ depth. Single NV center approximation indicated that the depth of the NV centers was approximately 9-10.7 nm from the surface with error of less than ±0.8 nm. Thus, a route for material control of shallow NV centers has been developed by step-flow growth using a CVD system. Our finding pioneers on the atomic level control of NV center alignment for large area quantum magnetometry.