Determination of local defect density in diamond by double electron-electron resonance
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-09-24 |
| Journal | Physical review. B./Physical review. B |
| Authors | Li Shang, Huijie Zheng, Zaili Peng, Mizuki Kamiya, Tomoyuki Niki |
| Institutions | University of Southern California, GSI Helmholtz Centre for Heavy Ion Research |
| Citations | 21 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details a local measurement technique utilizing Double Electron-Electron Resonance (DEER) combined with Optically Detected Magnetic Resonance (ODMR) to quantitatively determine defect concentrations in diamond.
- Core Achievement: Developed a local, quantitative method to measure the concentration of specific paramagnetic defect species, including single substitutional nitrogen (P1 centers), negatively charged nitrogen-vacancy (NV-) centers, and other g ~ 2 spins ([Ex]).
- Methodology: The technique uses NV- centers as probe spins (MW1) and applies a DEER pulse (MW2) to excite target defect spins (P1, Ex). The resulting phase shift in the NV- spin echo signal is analyzed to extract concentration data.
- Spatial Resolution: The ODMR setup provides high spatial resolution (laser spot size ~10 µm), enabling the characterization of local inhomogeneity.
- Key Finding (Inhomogeneity): Measurements on HPHT diamond samples revealed significant spatial variations in P1 concentration, ranging over an order of magnitude (e.g., 13 ppm to 322 ppm in sample S5).
- Engineering Relevance: This method is critical for understanding and controlling spin relaxation pathways (T1 and T2) in diamond, which directly limits the sensitivity of NV-based quantum sensors.
- Material Focus: The study characterized five HPHT synthetic diamond plates (S2, S5, D12, F32, E6) processed via electron-beam irradiation and thermal annealing.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Ground State Splitting (D) | 2.87 | GHz | Zero-field splitting constant |
| Laser Excitation Wavelength | 532 | nm | ODMR illumination source |
| Laser Spot Size (Resolution) | ~10 | µm | Confocal spatial resolution |
| External Magnetic Field (B0) | 22.7 | mT | Typical field used for ODMR/DEER |
| E-beam Irradiation Dose | ~1018 | cm-2 | Used for NV- creation |
| E-beam Energy Range | 3 to 14 | MeV | Used for NV- creation |
| Annealing Temperature Range | 700 to 1050 | °C | Thermal treatment post-irradiation |
| S5-1 T2 Coherence Time | 1.22 ± 0.02 | µs | Measured via Spin-Echo decay |
| S5-1 P1 Concentration ([P1]) | 37.5 ± 0.7 | ppm | Determined via DEER fit |
| S5-1 Ex Concentration ([Ex]) | 4.1 ± 0.2 | ppm | Determined via DEER fit (g ~ 2 spin) |
| S5-1 NV- Concentration ([NV-]) | 17 | ppm | Determined via DEER fit |
| Maximum P1 Spin-Flip Rate (Wmax) | 11 x 103 | s-1 | For [P1] = 37 ppm |
| P1 Concentration Range (S5 Sample) | 13 to 322 | ppm | Observed spatial inhomogeneity |
Key Methodologies
Section titled “Key Methodologies”The experiment relies on precise sample preparation and a specialized dual-microwave ODMR setup to perform DEER measurements.
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Sample Preparation (HPHT Diamond):
- Base Material: High-Pressure High-Temperature (HPHT) synthesized diamond plates.
- Orientation: Samples were either [100]-cut (D12, F32, E6, S5) or [111]-cut (S2).
- Vacancy Creation: Samples were irradiated using electron beams (3 MeV to 14 MeV) at high doses (~1018 cm-2) to create vacancies.
- NV Formation: Thermal annealing (700 °C to 1050 °C) was performed in forming gas (Ar/H2) for 2 to 16 hours to mobilize vacancies, allowing them to combine with nitrogen impurities (P1 centers) to form NV centers.
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ODMR/DEER Measurement Setup:
- Optical System: Confocal ODMR setup using a 532 nm laser for NV- initialization and readout (via photoluminescence, PL). PL is collected and filtered using a dichroic mirror and long-pass filter, detected by an avalanche photo-detector (APD).
- Microwave System: Two independent microwave sources (MW1 and MW2) are used, connected via transmission lines (~200 µm diameter, ~200 µm gap) placed on the diamond surface.
- Probe Sequence (MW1): MW1 drives the NV- centers (A spins) using a standard Spin Echo sequence (π/2 - τ - π - τ - π/2).
- DEER Pulse (MW2): MW2 drives the target spins (B spins, e.g., P1 centers) using a π pulse applied during the evolution time (τ) of the NV- Spin Echo.
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Data Acquisition and Analysis:
- Spectral Measurement: The DEER signal (change in NV- PL intensity) is recorded as a function of the MW2 frequency. Peaks in this spectrum correspond to the Electron Spin Resonance (ESR) frequencies of the target defects.
- Normalization: The raw signal (SIG) is normalized against two references (REF0, measured at very long evolution time; and REF1, measured without the DEER pulse) to obtain the normalized DEER signal (IDEER).
- Concentration Fitting: Defect concentration (n) is determined by fitting the IDEER spectrum using a theoretical model based on dipolar coupling and effective population transfer (Equation 5), treating n and the ESR linewidth (Δω) as fitting parameters.
Commercial Applications
Section titled “Commercial Applications”The ability to locally and quantitatively characterize defect concentrations is vital for optimizing diamond materials for advanced technological applications.
- Quantum Sensing and Metrology:
- Sensor Optimization: Guiding the synthesis of diamond with specific, low concentrations of P1 centers to maximize NV- spin coherence time (T2), thereby improving the sensitivity of magnetic, electric, and temperature sensors.
- Dense Ensembles: Essential for developing high-density NV ensembles required for high-sensitivity bulk sensing applications.
- Solid-State Quantum Computing:
- Decoherence Mitigation: Characterizing and controlling the concentration of parasitic spin baths (P1 centers) that cause decoherence in NV-based qubits.
- Advanced Material Characterization:
- Quality Control: Providing a high-resolution tool for mapping spatial homogeneity of impurities in large-area diamond wafers used in electronics or optics.
- Controlled Doping: Offering feedback for optimizing nitrogen incorporation and post-growth processing (irradiation, annealing) recipes to achieve desired defect ratios (e.g., high [NV-]/[P1] ratio).
- Diamond Electronics:
- Understanding how defect concentrations affect carrier mobility and thermal properties in diamond used for high-power RF or thermal management applications.
View Original Abstract
Magnetic impurities in diamond influence the relaxation properties and thus limit the sensitivity of magnetic, electric, strain, and temperature sensors based on nitrogen-vacancy color centers. Diamond samples may exhibit significant spatial variations in the impurity concentrations hindering the quantitative analysis of relaxation pathways. Here, we present a local measurement technique which can be used to determine the concentration of various species of defects by utilizing double electron-electron resonance. This method will help to improve the understanding of the physics underlying spin relaxation and guide the development of diamond samples, as well as offering protocols for optimized sensing.