| Metadata | Details |
|---|
| Publication Date | 2020-09-09 |
| Journal | Advanced Quantum Technologies |
| Authors | Max Gierth, Valentin Krespach, Alexander I. Shames, Priyanka Raghavan, Emanuel Druga |
| Institutions | City College of New York, Lawrence Berkeley National Laboratory |
| Citations | 13 |
| Analysis | Full AI Review Included |
- Record Hyperpolarization: High Temperature Annealing (HTA) at 1720 °C yields up to a 36x increase in 13C Dynamic Nuclear Polarization (DNP) enhancement compared to conventional 850 °C annealing, achieving an absolute 13C polarization of ~0.3%.
- Material Healing Mechanism: The significant DNP gain is attributed to HTA-driven healing of radiation damage in the diamond lattice, specifically suppressing adverse paramagnetic triplet defects (W33, W16-W18).
- Lifetime Improvement: HTA simultaneously increases the 13C nuclear spin-lattice relaxation time (T1) by 3-5x and the NV electron spin-lattice relaxation time (T1e) by ~10x, enabling higher saturation polarization levels.
- Optimal Recipe: The optimal HTA condition identified is 1720 °C for 15 minutes, which successfully harnesses high NV concentrations (up to 7 ppm) without the typical performance degradation seen in high-fluence, conventionally annealed samples.
- Multi-Modal Capability: HTA fortuitously endows the particles with multi-color fluorescence (UV, blue, green excitation) due to the formation of H3 and N3 centers, enabling simultaneous optical and enhanced MRI tracking.
- Guided Materials Production: This work establishes a systematic methodology, combining EPR and NMR relaxometry, for the guided production of high-quality, fluorescent, hyperpolarized nanodiamonds optimized for enhanced spectroscopy and imaging.
| Parameter | Value | Unit | Context |
|---|
| Optimal HTA Temperature | 1720 | °C | High Temperature Annealing condition |
| Optimal HTA Time | 15 | min | HTA duration for maximum DNP gain |
| Max DNP Enhancement (ε) | 230 | x | Relative to 7T Boltzmann (18 µm particles) |
| Absolute 13C Polarization | ~0.3 | % | Highest reported optical DNP level for crushed particles |
| Max DNP Signal Gain (HTA vs 850 °C) | 36 | x | Observed for high electron fluence (5x1019 e/cm2) samples |
| DNP Polarization Field (Bpol) | ~38 | mT | Optimal low magnetic field for optical pumping |
| NMR Detection Field | 7 | T | High magnetic field detection |
| Polarization Buildup Time | ~60 | s | Time to DNP saturation |
| 13C T1 Lifetime Increase | 3-5 | x | Factor increase due to HTA |
| NV T1e Lifetime Increase | ~10 | x | Factor increase due to HTA |
| Particle Size | 18 ± 3 | µm | Type Ib HPHT diamond microparticles used |
| Total Nitrogen Content | ~100 | ppm | Starting material specification |
| Optimal Electron Fluence | ~5 x 1018 | e/cm2 | Corresponds to ~4 ppm NV concentration (pre-HTA) |
| Optical Excitation Wavelength | 520 | nm | Laser pumping wavelength |
| Optical Power Density | ~570 | mW/mm2 | Excitation geometry (9 lasers) |
| Sample Shuttling Time | ~640 | ms | Time from DNP field to 7T detection field |
- Material Selection and Irradiation: Used Type Ib HPHT diamond particles (18 ± 3 µm, ~100 ppm N). Samples were subjected to controlled electron irradiation (1 MeV or 3 MeV) to generate vacancies, followed by conventional (850 °C for 2 hrs) or high-temperature annealing.
- High Temperature Annealing (HTA): Performed using an all-graphite furnace (MEO Engineering HTT-G10) capable of precise temperature control and rapid ramping.
- Conditions: Focused on the 1700-1800 °C range (optimal 1720 °C).
- Atmosphere: Majority of experiments performed in hydrogen atmosphere; vacuum environment was also tested for comparison.
- Ramping: Rapid heating (3 min) and cooling (3-5 min) times were employed to control defect evolution.
- Optical DNP Setup: Used a custom field cycling instrument interfaced with a 7T NMR magnet.
- Pumping: Continuous laser pumping (520 nm, 9 fiber-coupled diodes) was applied in an octagonal geometry to ensure uniform, near-hemispherical excitation of the sample (5-30 mg mass immersed in water).
- Transfer: Polarization transfer was achieved at a low field (~38 mT) using chirped microwave (MW) irradiation (200 sweeps/s) over the NV- EPR spectrum.
- NMR Detection and Relaxometry: Hyperpolarized 13C NMR signals were measured at 7T after rapid sample shuttling (~640 ms).
- T1 Mapping: A home-built field cycler device was used to map the 13C relaxation rate R1(B) across a wide field range (100 mT to 3 T) to spectrally fingerprint the relaxation mechanisms.
- Defect Characterization (EPR): Continuous wave X-band (9.4 GHz) EPR measurements were used to quantify concentrations of paramagnetic species, including NV- (W15), P1 centers, and secondary triplet defects (W33, W16-W18).
- Hyperpolarized MRI Agents: The 36x enhancement in 13C polarization drastically increases the signal-to-noise ratio (SNR) of diamond-based contrast agents, enabling substantial acceleration of MR imaging protocols for disease diagnosis and monitoring.
- Multi-Modal Bio-Imaging: HTA-optimized particles function as dual-mode agents, combining high-contrast hyperpolarized 13C MRI with bright, photostable, multi-color fluorescence (due to NV, H3, and N3 centers), crucial for high-fidelity particle tracking in-vivo.
- Quantum Magnetometry and Sensing: The significant increase in NV electron T1e and T2e coherence times resulting from HTA lattice healing is essential for developing high-density NV ensembles for ultrasensitive quantum sensors (e.g., magnetic and electric field, temperature, inertial rotation).
- Spin Polarization Relay Systems: Nanodiamonds (NDs) with enhanced 13C T1 lifetimes and high surface area are optimized to serve as efficient spin polarization relay channels, transferring polarization to external liquid nuclei (e.g., liquid coatings) via Overhauser contact for external DNP applications.
- Solid-State Quantum Computing: The demonstrated ability to precisely manipulate and optimize lattice defects (NV centers) and coherence times via HTA opens new avenues for fabricating materials suitable for quantum computing platforms in solids.
View Original Abstract
Abstract Methods of optical dynamic nuclear polarization open the door to the replenishable hyperpolarization of nuclear spins, boosting their nuclear magnetic resonance/imaging signatures by orders of magnitude. Nanodiamond powder rich in negatively charged nitrogen vacancy defect centers has recently emerged as one such promising platform, wherein 13 C nuclei can be hyperpolarized through the optically pumped defects completely at room temperature. Given the compelling possibility of relaying this 13 C polarization to nuclei in external liquids, there is an urgent need for the engineered production of highly “hyperpolarizable” diamond particles. Here, a systematic study of various material dimensions affecting optical 13 C hyperpolarization in diamond particles is reported on. It is discovered surprisingly that diamond annealing at elevated temperatures ∼1720 °C has remarkable effects on the hyperpolarization levels enhancing them by above an order of magnitude over materials annealed through conventional means. It is demonstrated these gains arise from a simultaneous improvement in NV − electron relaxation/coherence times, as well as the reduction of paramagnetic content, and an increase in 13 C relaxation lifetimes. This work suggests methods for the guided materials production of fluorescent, 13 C hyperpolarized, nanodiamonds and pathways for their use as multimodal (optical and magnetic resonance) imaging and hyperpolarization agents.