Electron spin resonance of NV-=SUP=-(-)-=/SUP=--centers in synthetic fluorescent diamond microcrystals under conditions of optical spin polarization
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Оптика и спектроскопия |
| Authors | V. Yu. Osipov, Kirill Bogdanov, Arfaan Rampersaud, Kazuyuki Takai, Yasushi Ishiguro |
| Institutions | Hosei University, Tokyo Denki University |
| Analysis | Full AI Review Included |
Electron Spin Resonance of NV--Centers in Synthetic Fluorescent Diamond Microcrystals under Conditions of Optical Spin Polarization
Section titled “Electron Spin Resonance of NV--Centers in Synthetic Fluorescent Diamond Microcrystals under Conditions of Optical Spin Polarization”Executive Summary
Section titled “Executive Summary”This research investigates the use of Optical Spin Polarization (OSP) to enhance the diagnostic capabilities of Electron Paramagnetic Resonance (EPR) spectroscopy for synthetic Nitrogen-Vacancy (NV-) diamond microcrystals.
- Core Achievement: Demonstrated significant amplification of NV- EPR signals (up to 6 times) by illuminating the material with broadband light (xenon lamp) at low temperatures (~100 K).
- Amplification Results: The low-field allowed transitions (Δms = 1) were amplified 5-6 times, while the “forbidden” transitions (Δms = 2) increased 2.5-3 times.
- Mechanism Confirmation: The amplification is attributed to a change in the population of the ground triplet state (3A2) levels, specifically the optical polarization of spins into the ms = 0 sublevel.
- Selectivity: The EPR signals from other major defects, such as paramagnetic nitrogen (P1 centers) and impurity nickel (Nis-), remained practically unchanged (within 2%), confirming the effect is specific to the NV- centers.
- Diagnostic Value: This OSP-enhanced EPR technique serves as a sensitive diagnostic method for selecting premium diamond microcrystals characterized by high crystalline quality, low internal stresses, and low foreign metal impurity content, crucial for advanced sensor applications.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Type | Synthetic Ib HPHT | N/A | Starting material (Columbus Nanoworks Ltd.) |
| NV- Concentration | ~3.8 | ppm | Measured defect density in final material |
| Substitutional N (P1) Concentration | 140 ± 10 | ppm | Primary dopant concentration |
| Impurity Nickel Concentration | 4.3 | ppm | Measured Nis- concentration |
| Initial Crystal Size | 200-350 | µm | Before mechanical processing |
| Milled Particle Size (Average) | ~13 | µm | Final sample size (#7381-b) |
| Electron Irradiation Energy | > 2 | MeV | Used for vacancy creation |
| Electron Irradiation Dose | ~6 x 1018 | e-/cm2 | Required dose for NV formation |
| Annealing Temperature | 800 | °C | Post-irradiation treatment (6 hours) |
| Etching Temperature | 450 | °C | Gas-phase oxidation in air (1 hour) to remove sp2 carbon |
| EPR Measurement Temperature | 90-100 | K | Operating temperature range (stabilized to 0.03 K) |
| EPR Microwave Frequency | ~9.04 | GHz | X-band spectrometer |
| EPR Microwave Power | 0.003 | mW | Power used for spectral recording |
| Δms = 1 Signal Amplification | 5-6 | Times | Enhancement factor under OSP (low-field allowed transitions) |
| Δms = 2 Signal Amplification | 2.5-3 | Times | Enhancement factor under OSP (“forbidden” transitions) |
| Effective OSP Photon Energy | 2 to 3 | eV | Corresponds to light with wavelength λ < 640 nm |
| Diamond Raman Shift | 1332 | cm-1 | Indicates high crystalline quality |
Key Methodologies
Section titled “Key Methodologies”The study involved a multi-step process for sample preparation and advanced EPR/optical characterization:
- HPHT Synthesis: Microcrystals were grown under high pressures (> 5 GPa) and high temperatures (> 1350 °C) using a nickel-containing metal catalyst.
- NV- Center Formation:
- Crystals were irradiated with a high-energy electron beam (> 2 MeV) at a dose of ~6 x 1018 e-/cm2 to create vacancies.
- Irradiated crystals were subsequently annealed at 800 °C for 6 hours in an inert atmosphere to mobilize vacancies and form NV centers.
- Milling and Purification:
- Crystals were powdered in a planetary mill to an average size of ~13 µm.
- The powder was cleaned in boiling acids to remove metal inclusions.
- Surface defects (sp2 carbon) were removed via gas-phase etching (oxidation in air) at 450 °C for 1 hour.
- EPR Spectroscopy Setup:
- Measurements were performed using a JEOL-JES-FA300 EPR spectrometer equipped with a flow-type cryostat (T = 100 K).
- Standard parameters: 9.04 GHz microwave frequency, 0.07 mT magnetic field modulation, 0.003 mW microwave power.
- Optical Spin Polarization (OSP) Induction:
- The sample was illuminated in situ using a 500 W xenon discharge lamp.
- Broadband (HA30 filter, 300-900 nm) and short-wavelength (L42 filter, λ > 420 nm) light were used, confirming that photons with energies between 2 and 3 eV are responsible for the OSP effect.
- Luminescence and Raman Analysis:
- Luminescence spectra (excited by 488 nm laser) confirmed the predominant presence (up to 98%) of the negatively charged NV- state (Zero-Phonon Line at 638 nm).
- Raman spectroscopy confirmed high lattice quality via a narrow 1332 cm-1 line (3.4 cm-1 wide).
Commercial Applications
Section titled “Commercial Applications”The ability to accurately diagnose and select high-quality NV- diamond microcrystals using OSP-enhanced EPR is critical for several high-tech engineering fields:
- Quantum Sensing and Metrology:
- High-Sensitivity Magnetometers: NV- centers are the basis for highly sensitive magnetic field sensors used in medical diagnostics (MRI), fundamental physics, and non-destructive testing.
- Temperature and Strain Sensors: Utilizing the spin properties of NV- centers to create robust, localized sensors for measuring temperature and mechanical strain in extreme environments.
- Quantum Information Technology (QIT):
- Solid-State Qubits: High-quality NV- centers with long spin coherence times are essential for developing solid-state quantum memory and quantum computing architectures.
- Micro- and Nanophotonics:
- Single-Photon Sources: NV- centers are stable single-photon emitters, crucial for quantum cryptography and quantum communication systems.
- Fiber Optic Integration: Small NV- microcrystals (< 30 µm) can be integrated directly into the core or ends of optical fibers, creating active sensing elements for remote monitoring.
- Bio-Imaging and Nanomedicine:
- Intracellular Tracking: NV- diamond nanoparticles are used as biocompatible, non-toxic fluorescent markers for high-resolution visualization and tracking of single organelles and neurons in vivo.
- Material Quality Control (QC):
- The OSP-EPR method provides a powerful QC tool for manufacturers of synthetic diamond, allowing them to verify low levels of internal stress and foreign impurities (Ni, N) necessary for premium-grade sensor materials.
View Original Abstract
Electron paramagnetic resonance (EPR) spectra of synthetic diamond microcrystals with NV (-) -centers have been studied. It is shown that under the conditions of irradiation of the material with the light of a xenon lamp at low temperatures ~ 100 K, the intensities of the EPR signals corresponding to the &quot;forbidden&quot; (Delta m s =2) and low field allowed (Delta m s =1) transitions are amplified several times, while the EPR signals from paramagnetic nitrogen and impurity nickel in the charge state -1 practically do not change. This is due to a change in the population of levels of the ground triplet state of the NV (-) - center and the optical polarization of spins in the state m s =0 of the triplet level. Keywords: nitrogen-vacancy centers, synthetic diamond, electron paramagnetic resonance, spin polarization, luminescence.