Идентификация NV-центров в синтетических флуоресцентных наноалмазах и контроль дефектности кристаллитов методом электронного парамагнитного резонанса
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-12-09 |
| Journal | Оптика и спектроскопия |
| Authors | В.Ю. Осипов, К.В. Богданов, François Treussart, Arfaan Rampersaud, А.В. Баранов |
| Institutions | Columbus NanoWorks (United States), Centre National de la Recherche Scientifique |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study investigates Nitrogen-Vacancy (NV) centers in synthetic fluorescent nanodiamonds (FNDs) to establish quality control metrics for advanced applications.
- Material Focus: Synthetic HPHT Ib nanodiamond particles (average size ~100 nm) containing high concentrations of NV centers (up to 5.5 ppm).
- Core Achievement: Successful identification and quantification of NV- triplet centers (W15) using Electron Paramagnetic Resonance (EPR) spectroscopy, specifically monitoring the forbidden (Delta ms = 2) and allowed (Delta ms = 1) transitions.
- Quality Control Method: The saturation curve of the forbidden Delta ms = 2 EPR transition is shown to be highly sensitive to the local crystalline quality and the presence of near-surface defects. This method enables the selection of FND batches with superior crystal quality.
- Correlation Established: The integrated intensity of the EPR signal (g = 4.27) correlates directly with the overall photoluminescence (PL) intensity in the 600-800 nm range, confirming the effectiveness of electron irradiation dose in creating active NV- centers.
- Defect Tolerance: The 100 nm FNDs, despite mechanical milling, show high crystal quality near the NV centers, suggesting that surface defects (like multi-vacancies) do not significantly quench the NV- luminescence or drastically shorten spin relaxation times.
- Engineering Value: The EPR saturation technique provides a non-optical diagnostic tool for rapid assessment and selection of high-quality FND powders for use in nanophotonics and quantum sensing.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nanodiamond Size (Mean) | 104 | nm | Submicron fraction used for irradiation. |
| Nanodiamond Size (FWHM) | ~76 | nm | Width of particle size distribution. |
| Starting Nitrogen Conc. | 150 ± 10 | ppm | In bulk HPHT Ib microcrystals. |
| Irradiation Energy | 5 | MeV | High-energy electron beam used to create vacancies. |
| Electron Current Density | 32 | µA/cm2 | Used during irradiation process. |
| Annealing Temperature | 800 | °C | Used in inert atmosphere to mobilize vacancies. |
| Max NV- Concentration | 5.5 | ppm | Achieved in the highest dose sample (FND-3). |
| EPR Frequency (X-band) | ~9.43 | GHz | Operating frequency of the JEOL JES-FA 300 spectrometer. |
| NV- ZFS Parameter (D) | 954 x 10-4 | cm-1 | Zero-Field Splitting of the 3A2 ground state. |
| NV- ZFS (Frequency) | 2.87 | GHz | Equivalent frequency of the zero-field splitting. |
| PL Excitation Wavelength | 532 | nm | Used for micro-Raman/PL measurements. |
| NV- ZPL Emission | 638 | nm | Zero Phonon Line (ZPL) of the NV- center. |
| Raman Line Width (FND) | 2.0-2.7 | cm-1 | Observed in 75-100 nm FNDs (compared to <1 cm-1 in bulk). |
| EPR Saturation Power (FMD) | 0.2-0.3 | mW | Power at which the g = 4.27 signal saturates in micron-sized diamonds (FMD). |
| EPR Saturation Power (FND) | >0.4 | mW | Power at which the g = 4.27 signal saturates in 100 nm FNDs. |
Key Methodologies
Section titled “Key Methodologies”The fluorescent nanodiamonds (FNDs) were synthesized and characterized using a multi-step process combining mechanical, thermal, and spectroscopic techniques:
-
Milling and Sizing:
- Starting material: HPHT Ib diamond microcrystals (up to 150 µm grain size).
- Process: Intensive crushing and milling (grinding) to produce submicron powder.
- Selection: Centrifugation in aqueous media was used to isolate the desired 100 nm fraction (mean size 104 nm).
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Vacancy Creation (Irradiation):
- Method: High-energy electron beam irradiation (5 MeV).
- Purpose: To displace carbon atoms and create vacancies in the diamond lattice.
- Doses: Samples FND-1, FND-2, and FND-3 received increasing cumulative exposures (16 h, 32 h, 40 h, respectively).
-
NV Center Formation (Annealing):
- Method: Thermal annealing (отжиг).
- Conditions: 800 °C in an inert atmosphere.
- Purpose: To mobilize the created vacancies, allowing them to migrate and be captured by isolated substitutional nitrogen impurities (P1 centers), forming the NV- centers.
-
Purification:
- Method: Intensive chemical cleaning in boiling acids.
- Purpose: Removal of parasitic metallic impurities, primarily iron-containing complexes, which interfere with EPR measurements.
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EPR Spectroscopy (Characterization):
- Instrument: JEOL JES-FA 300 spectrometer (X-band, ~9.43 GHz).
- Measurements: Spectra were recorded at room temperature.
- Quantification: NV- concentration was determined by double integration of the g = 4.27 signal (Delta ms = 2 forbidden transition) relative to known standards.
- Quality Assessment: Saturation curves (EPR intensity vs. square root of microwave power) were analyzed to assess spin relaxation times and local crystal quality.
-
Optical Characterization (PL):
- Instrument: Renishaw inVia micro-Raman system and custom video-microscopes (TIRF, DIC).
- Measurements: PL spectra (600-800 nm) were recorded using 532 nm excitation.
- Purpose: To confirm the presence of optically active NV- centers (ZPL at 638 nm) and correlate PL intensity with EPR-derived NV- concentration.
Commercial Applications
Section titled “Commercial Applications”The characterized high-quality fluorescent nanodiamonds containing high concentrations of NV centers are critical enabling materials for several high-tech and emerging industries:
| Industry/Sector | Specific Application | Technical Requirement Met |
|---|---|---|
| Quantum Sensing | Magnetic field, temperature, and strain sensing at the nanoscale (e.g., cellular level). | High NV- concentration and long spin coherence times (indicated by favorable EPR saturation behavior). |
| Nanophotonics | Single-photon sources, integrated optical circuits, and protected communication channels. | Stable, bright, and non-quenched luminescence from NV centers embedded in nanostructures. |
| Biomedicine | Bioimaging, cellular tracking (tracking movement of cells), and targeted drug delivery. | Small particle size (~100 nm) for cellular uptake, combined with bright, non-toxic fluorescence. |
| Telecommunications | Quantum repeaters and memory elements in quantum networks. | High crystal quality in the vicinity of the NV center, ensuring stable electronic properties and long relaxation times. |
| Materials Diagnostics | Non-optical quality control of diamond powders and films. | Use of EPR saturation curves as a rapid, non-destructive method to screen material quality before deployment. |
View Original Abstract
A 100 nm synthetic diamond particle with a large (> 4 ppm) amount of nitrogen vacancy (NV) centers has been studied. The latter exhibit lines associated with forbidden Delta m_s = 2 and allowed Delta m_s = 1 transitions in the electron paramagnetic resonance (EPR) spectra of the ground state of the NV(-) center. The luminescence intensity of particles in the range 550-800 nm increases with an increase in the irradiation dose of 5 MeV electrons and correlates with the integrated intensity of the EPR line with a g-factor g = 4.27.This value is used to estimate the concentration of NV(-) centers and to select diamond powders with the highest fluorescence intensity. The dependence of the EPR signal intensity of the Delta m_s = 2 transition of the NV(-) center on the microwave power has the form of a curve with saturation and subsequent decay, and rather well characterizes the crystal quality of the local environment of the centers under study in these particles. The intensity of the x,y Delta m_s = 1 transition (at ~281.2 mT, 9.444 GHz) turns out to be more sensitive to changes in particle size in the submicron range and the appearance of near-surface defects obtained during mechanical processing.