Contributed Review - Camera-limits for wide-field magnetic resonance imaging with a nitrogen-vacancy spin sensor
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-03-01 |
| Journal | Review of Scientific Instruments |
| Authors | Adam M. Wojciechowski, MĂŒrsel Karadas, Alexander Huck, Christian Osterkamp, Steffen Jankuhn |
| Institutions | Technical University of Denmark, Leipzig University |
| Citations | 33 |
| Analysis | Full AI Review Included |
Wide-Field Nanotesla Magnetometry via MPCVD NV Diamond
Section titled âWide-Field Nanotesla Magnetometry via MPCVD NV DiamondâResearch Paper Analysis: Camera-limits for wide-field magnetic resonance imaging of a nitrogen-vacancy spin sensor (arXiv:1708.06317v1)
Executive Summary
Section titled âExecutive SummaryâThis research establishes the critical role of detector technologyâspecifically Full Well Capacity (FWC) and Frame Rate (FPS)âin achieving real-time, high-sensitivity wide-field magnetometry using Nitrogen-Vacancy (NV) centers in diamond.
- Application Validation: Confirms the feasibility of nanotesla-level magnetic field sensing at video frame rates (60 FPS) with micrometer spatial resolution using ensembles of NV centers.
- Sensitivity Achieved: Demonstrated a bandwidth-normalized magnetic sensitivity of 142 nT Hz-1/2 per single pixel, achieving 1 ”T sensitivity in a single 16.7 ms frame.
- Material Requirements: Success hinges on using high-purity, isotopically engineered Single Crystal Diamond (SCD) with a thin, controlled NV sensing layer (1 ”m thickness) grown via MPCVD.
- Technological Advancement: Proves the significant advantage of specialized lock-in CMOS cameras, which enable phase-sensitive demodulation and background subtraction, drastically improving Signal-to-Noise Ratio (SNR) compared to standard scientific cameras.
- SNR Limitation: The practical sensitivity is limited by the maximum number of photoelectrons a pixel can collect (FWC), dictating the achievable optical shot-noise limit ($\text{SNR} \propto \sqrt{\text{FWC}}$).
- 6CCVD Value Proposition: 6CCVD specializes in the precise SCD engineering required for NV ensemble sensing, offering custom growth, isotopic purification, and post-processing services (implantation, annealing, metalization).
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the material parameters and performance metrics required and achieved in the study:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensing Volume Dimensions | 2 x 2 x 0.5 | mm3 | SCD Substrate Size |
| NV Layer Thickness | 1 | ”m | MPCVD Grown Layer |
| Isotopic Purity (12C) | > 99.99 | % | Required for long spin coherence time ($T_2$) |
| Nitrogen Doping (15N) | ~10 | ppm | Concentration in the sensing layer |
| Vacancy Implantation Dose | ~1015 | cm-2 | 1.8 MeV Helium ions |
| NV Concentration (Estimated) | ~1 | ppm | Resulting sensor density |
| ODMR Contrast (C) | ~5 | % | Used in sensitivity calculations |
| Resonance Linewidth ($\Gamma/2\pi$) | 1 | MHz | Assumed value for sensitivity estimation |
| Single-Frame Sensitivity ($\delta B^{exp}_{px, \max}$) | 1 | ”T | Single pixel, 60 FPS acquisition |
| Bandwidth-Normalized Sensitivity | 142 | nT Hz-1/2 | Lock-in camera performance at 59.7 FPS |
| Pixel Size (at Diamond Plane) | ~0.9 | ”m | High-magnification setup |
| Spatial Resolution (Actual) | ~2 | ”m | Limited by objective optics (NA=0.7) |
| Required Optical Power (Full Sensor) | 1.0 | mW | For lock-in camera (#5) maximum sensitivity |
| Lock-in Camera FWC | 3.5 x 105 | e- | Heliotis heliCam C3 |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on highly controlled material preparation combined with specialized optical detection:
- Diamond Substrate: Used electronic-grade SCD (2x2x0.5 mm3).
- MPCVD Growth: A 1 ”m thick layer of isotopically purified 12C diamond (purity > 99.99%) containing 15N (~10 ppm) was grown via MPCVD on the substrate surface.
- Vacancy Creation: Vacancies were introduced by 1.8 MeV Helium ion implantation (~1015 cm-2 dose).
- Annealing: Samples were annealed for 2 hours in vacuum at 900°C to mobilize vacancies and form NV centers (estimated final concentration ~1 ppm).
- Surface Engineering:
- The top surface (excitation/collection side) was coated with a 300 nm aluminum layer to act as a reflective mirror for increased excitation and fluorescence collection efficiency.
- The bottom side was anti-reflection coated with silica to minimize internal reflection losses.
- ODMR Measurement: Continuous-wave (cw) ODMR was performed in an inverted microscope setup (NA=0.7 objective). A uniform 2 mT bias magnetic field was applied parallel to the [110] direction.
- MW Delivery: MWs were generated, TTL-modulated at 3.7 kHz, amplified, and delivered via a printed circuit-board antenna located 1 mm from the NV layer.
- Detection: A specialized lock-in CMOS camera (Heliotis heliCam C3, sensor #5) was used, set to accumulate charge over 62 modulation periods (59.7 FPS), employing phase-sensitive demodulation and background subtraction to maximize SNR and effective FWC usage.
- Data Processing: ODMR spectra were fitted to double-Lorentzian curves to extract frequency shift (proportional to field change) and calculate SNR maps from fitted amplitude parameters and noise data acquired without MWs.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research demonstrates a clear demand for highly customized, precision-engineered MPCVD diamond layers. 6CCVD is uniquely positioned to supply the materials necessary to replicate and advance this nanotesla wide-field magnetometry work.
Applicable Materials
Section titled âApplicable MaterialsâReplicating this high-sensitivity NV sensor requires diamond engineered specifically to maximize ODMR contrast ($C$) and spin coherence ($T_2$).
| Material Requirement (Paper) | 6CCVD Optimized Solution | Value Proposition |
|---|---|---|
| Isotopic Purity (12C > 99.99%) | High-Purity Isotopic SCD Wafers | Essential for achieving long $T_2$ times (> 1 ”s), which fundamentally limit spin-projection noise ($\delta B \propto 1/\sqrt{T_2}$). |
| Controlled 15N Doping | Precision N-Doped SCD Layer (1-10 ppm) | 6CCVD offers tight control over 15N concentration and depth during MPCVD growth, ensuring high, uniform NV density and maximizing the magnetic signal contrast. |
| Thin Sensing Layer (1 ”m) | Custom Epitaxial Layer Thickness (SCD) | We guarantee SCD growth thicknesses down to 0.1 ”m with high uniformity, vital for 2D field mapping and micrometer spatial resolution. |
| Substrates | MPCVD Substrates (up to 10 mm thick) | Supplied high-quality SCD or PCD substrates suitable for subsequent growth, implantation, and annealing processes. |
Customization Potential
Section titled âCustomization PotentialâThe experiment utilized complex post-processing steps, all of which fall within 6CCVDâs advanced engineering scope.
- Custom Dimensions: The 2x2 mm2 sample size is achievable via our precision laser cutting service. We provide custom plates/wafers up to 125 mm (PCD) and full SCD wafers for wide-field imaging arrays.
- Precision Metalization: The use of a 300 nm reflective aluminum (Al) layer is critical for photon collection. 6CCVD offers custom thin-film metalization services including Au, Pt, Ti, W, and, specifically, Al deposition tailored for optimized reflection/anti-reflection coatings or antenna contacts.
- Surface Finish: Achieving high collection efficiency requires minimal light scattering. 6CCVD guarantees ultra-smooth SCD surface polishing with Ra < 1 nm, critical for integrating reflection coatings and high-NA imaging optics.
- Post-Processing Integration: While ion implantation is often outsourced, 6CCVDâs process control ensures that our materials are optimized for subsequent high-temperature annealing (900°C) cycles required for high NV conversion yield.
Engineering Support
Section titled âEngineering SupportâThe trade-off between NV concentration, coherence time, layer thickness, and ODMR contrast is complex. 6CCVDâs in-house PhD team provides expert support to optimize these parameters for specific research goals.
- Application-Specific Material Design: Our engineers assist clients designing diamond layers for similar quantum sensing and wide-field magnetometry projects, ensuring the MPCVD growth recipe maximizes the figure of merit ($\delta B \propto \Gamma / (C \cdot \text{SNR})$).
- Detector Matching: We provide consultation on optimizing diamond layer thickness and NV concentration to match the FWC limits of specific high-speed or deep-well cameras, maximizing the optical power utilization (up to 10 mW total optical power required for the highest sensitivity camera analyzed).
- Global Logistics: We provide global shipping (DDU default, DDP available) to ensure timely delivery of custom-engineered materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Sensitive, real-time optical magnetometry with nitrogen-vacancy centers in diamond relies on accurate imaging of small (âȘ10â2), fractional fluorescence changes across the diamond sample. We discuss the limitations on magnetic field sensitivity resulting from the limited number of photoelectrons that a camera can record in a given time. Several types of camera sensors are analyzed, and the smallest measurable magnetic field change is estimated for each type. We show that most common sensors are of a limited use in such applications, while certain highly specific cameras allow achieving nanotesla-level sensitivity in 1 s of a combined exposure. Finally, we demonstrate the results obtained with a lock-in camera that paves the way for real-time, wide-field magnetometry at the nanotesla level and with a micrometer resolution.