Optical hyperpolarization of nitrogen donor spins in bulk diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-02-14 |
| Journal | Physical review. B./Physical review. B |
| Authors | M. Loretz, H. Takahashi, Takuya F. Segawa, J. M. Boss, Christian L. Degen |
| Institutions | ETH Zurich |
| Citations | 17 |
| Analysis | Full AI Review Included |
Technical Documentation: Hyperpolarized Diamond Materials for DNP
Section titled âTechnical Documentation: Hyperpolarized Diamond Materials for DNPâSource Paper: Optical hyperpolarization of nitrogen donor spins in bulk diamond (Loretz et al., 2016/2022)
6CCVD Ref: Hyperpolarization of P1 Centers for Enhanced Dynamic Nuclear Polarization (DNP)
Executive Summary
Section titled âExecutive SummaryâThis study successfully demonstrates a critical step toward enhancing the efficiency of diamond-based Dynamic Nuclear Polarization (DNP) devices by hyperpolarizing bulk substitutional nitrogen (P1) defects.
- Mechanism Demonstrated: Hyperpolarization of P1 centers (N°) achieved through optical pumping of Nitrogen-Vacancy (NV¯) centers coupled via rapid cross-relaxation at an energy level matching condition ($B = 51 \text{ mT}$).
- Performance Metrics: Achieved a substantial P1 spin polarization of 0.9%, corresponding to a robust enhancement factor of 25x relative to the thermal Boltzmann polarization.
- Material Utilization: This approach leverages the high concentration of P1 centers (up to 77 ppm), which act as an abundant resource for high electronic spin polarization in bulk diamond.
- Application Relevance: Hyperpolarized P1 centers form a useful resource for charge state conversion processes, significantly increasing the efficiency and feasibility of room-temperature, diamond-based DNP systems for high-sensitivity NMR.
- Technical Challenge: The observed polarization enhancement unexpectedly saturates at very low laser intensities (~10 mW/mmÂČ), indicating the necessity of advanced defect engineering and pulsed excitation schemes to overcome charge state conversion limitations.
Technical Specifications
Section titled âTechnical SpecificationsâThe following critical parameters and performance metrics were extracted from the experimental data, focusing on Chip A.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Magnetic Bias Field (B) | 51 | mT | Required for NV¯/N° cross-relaxation matching |
| Optical Pumping Wavelength | 532 | nm | CW Green Laser Illumination |
| Maximum N° (P1 Center) Polarization | 0.9 | % | Achieved at 300 mW laser power |
| N° Polarization Enhancement Factor | 25 | N/A | Enhancement over Boltzmann polarization |
| Maximum NVÂŻ Polarization | 3.5 | % | Achieved at 300 mW laser power |
| NVÂŻ Polarization Enhancement Factor | 103 | N/A | Enhancement over Boltzmann polarization |
| Material Used | Type Ib HPHT Diamond | N/A | Bulk diamond material |
| N° (P1 Center) Density (Chip A) | 77 | ppm | 1020 cm-3 density achieved |
| NVÂŻ Center Density (Chip A) | 9 | ppm | Total density post-irradiation/annealing |
| Anomalous Saturation Threshold | ~10 | mW/mm2 | Polarization ceases to increase above this intensity |
| Annealing Temperature | 850 | °C | Required step for defect formation |
| Operating Temperature | ~200 | K | Achieved via cold N2 gas flow |
| Chip Dimensions (Lateral) | 3 x 3 | mm2 | Used in the EPR setup |
| Chip Thickness (Chip A) | 0.3 | mm | Sample thickness |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material preparation, controlled defect creation, and low-frequency EPR spectroscopy.
- Diamond Selection: High-nitrogen (Type Ib) diamond chips grown by High-Pressure/High-Temperature (HPHT) synthesis were selected, featuring exposed (100) surfaces.
- Defect Creation: Samples were irradiated using a 2 MeV electron beam for a total duration of 30 h to 40 h to create vacancies, which subsequently formed NV and P1 centers upon annealing.
- Post-Irradiation Annealing: Annealing was performed in high vacuum at 850°C for 2 h to mobilize vacancies and convert P1 centers into NV centers (while retaining high P1 concentrations).
- EPR Setup: In situ Electron Paramagnetic Resonance (EPR) spectroscopy was conducted at 51 mT using a custom-built low-frequency setup (1.44 MHz) utilizing an inductively coupled loop gap resonator.
- Magnetic Field Orientation: The diamond crystal was precisely oriented (35° tilt, 45° rotation) to align the magnetic field along one of the [111] crystal axes, maximizing the efficiency of the optical pumping mechanism for aligned NV centers.
- Optical Pumping and Cooling: CW 532 nm laser light (up to 1 W) was directed onto the diamond surface. Absorptive heating was managed by flowing cold nitrogen gas (~200 K) over the chip.
- Polarization Transfer: Hyperpolarization was achieved by driving the cross-relaxation process between the optically pumped NV¯ centers (ms = 0 $\leftrightarrow$ ms = -1 transition) and the substitutional nitrogen defects (N°).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the engineered diamond platforms required to replicate, optimize, and scale this groundbreaking work in hyperpolarization and quantum technologies. Our Microwave Plasma Chemical Vapor Deposition (MPCVD) materials offer enhanced control over crystal purity, orientation, and defect concentration compared to the HPHT material used in the study.
| Applicable Materials & Requirements | 6CCVD Solution & Capability | Engineering and Sales Advantage |
|---|---|---|
| Type Ib Material Replication (High N content, 77 ppm) | High-Nitrogen SCD & PCD (Custom Doped) | We offer highly controlled nitrogen incorporation during MPCVD growth, providing far greater spatial uniformity and repeatable P1 concentrations compared to bulk HPHT. This ensures consistent defect creation post-irradiation. |
| Precise Dimensions (3 x 3 mm2, 0.3 mm thickness) | Custom Dimensions & Thickness Control | 6CCVD delivers SCD plates (0.1 ”m - 500 ”m) and PCD wafers up to 125 mm lateral size. We can provide materials pre-cut or laser-etched to fit specific EPR/DNP resonator geometries. |
| Superior Crystal Quality & Orientation ([100] surface used) | High-Purity SCD (Ra < 1 nm Polishing) | To minimize surface traps (which affect charge state conversion), we provide ultra-low roughness SCD (Ra < 1 nm) and precision-oriented crystals, including standard [100] and optimized [111] cuts. |
| Mitigating Saturation / Charge State Control | Boron-Doped Diamond (BDD) Wafers | The saturation is linked to charge state conversions (NVÂŻ $\leftrightarrow$ NV°, N° $\leftrightarrow$ Nâș). Integrating BDD material into the device stack allows for electrical tuning of the Fermi level, which can suppress or mitigate undesirable charge state conversions, thereby increasing the maximum achievable polarization. |
| Future DNP Integration (Surface transfer / spin labels) | Custom Metalization Capabilities | For advanced DNP devices requiring integrated control structures or micro-coils, we offer in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu deposition, crucial for creating reliable surface interfaces and electrodes. |
| Scale-Up and Volume Requirements | Global Shipping & Supply Chain | We support academic and commercial partners with reliable, DDU or DDP global shipping of high-volume and custom diamond orders, reducing logistical burden for international research teams. |
Engineering Support: 6CCVDâs in-house PhD team specializes in optimizing defect creation protocols (nitrogen insertion and post-growth processing) necessary for maximizing the T1 and T2 coherence times required for efficient bulk hyperpolarization and subsequent transfer in Dynamic Nuclear Polarization (DNP) projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We report hyperpolarization of the electronic spins associated with\nsubstitutional nitrogen defects in bulk diamond crystal. Hyperpolarization is\nachieved by optical pumping of nitrogen vacancy centers followed by rapid cross\nrelaxation at the energy level matching condition in a 51 mT bias field. The\nmaximum observed donor spin polarization is 0.9 \% corresponding to an\nenhancement by 25 compared to the thermal Boltzmann polarization. A further\naccumulation of polarization is impeded by an anomalous optical saturation\neffect that we attribute to charge state conversion processes. Hyperpolarized\nnitrogen donors may form a useful resource for increasing the efficiency of\ndiamond-based dynamic nuclear polarization devices.\n