Electron–electron double resonance detected NMR spectroscopy using ensemble NV centers at 230 GHz and 8.3 T
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-08-23 |
| Journal | Journal of Applied Physics |
| Authors | Benjamin Fortman, Laura Mugica-Sanchez, Noah Tischler, Cooper Selco, Yuxiao Hang |
| Institutions | University of Southern California, University of California, Los Angeles |
| Citations | 25 |
| Analysis | Full AI Review Included |
Technical Documentation: High-Field NV-Detected EDNMR Spectroscopy
Section titled “Technical Documentation: High-Field NV-Detected EDNMR Spectroscopy”This document analyzes the research demonstrating Electron-Electron Double Resonance Detected NMR (EDNMR) using ensemble Nitrogen-Vacancy (NV) centers at high magnetic fields (8.3 Tesla, 230 GHz). This breakthrough establishes a critical methodology for nanoscale NMR, directly aligning with 6CCVD’s expertise in high-purity, custom MPCVD diamond materials for quantum and magnetic sensing applications.
Executive Summary
Section titled “Executive Summary”- High-Field Sensing Demonstrated: Successful implementation of Optically Detected Magnetic Resonance (ODMR) and the first measurement of Electron-Electron Double Resonance Detected NMR (EDNMR) using ensemble NV centers at 8.3 Tesla (230 GHz).
- Nanoscale NMR Feasibility: The technique successfully detected 13C nuclear bath spins, validating a robust method for nanoscale NMR at high magnetic fields, which significantly improves spectral resolution over low-field methods.
- T1 Limited Advantage: EDNMR is limited by the longitudinal relaxation time (T1 ~ 3.9 ms), rather than the shorter transverse relaxation time (T2), allowing for longer High Turning Angle (HTA) pulses and enhanced sensitivity, especially at cryogenic temperatures where T1 can extend to seconds.
- Material Purity Critical: Spectral linewidth (Δω) was found to be limited by the concentration of paramagnetic impurities, specifically P1 centers (~70 ppm), necessitating the use of high-purity, isotopically engineered diamond for future improvements.
- Future Applications: The method is directly applicable to detecting external spins (e.g., 1H, 19F) near the diamond surface, requiring high-quality SCD substrates optimized for shallow NV creation (> 8 nm depth).
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Magnetic Field (B0) | 8.306 | Tesla (T) | Operating field for ODMR/EDNMR |
| NV Larmor Frequency | 230 | GHz | Highest frequency demonstrated to date |
| Equivalent 1H NMR Frequency | 350 | MHz | Corresponds to the 230 GHz NV Larmor frequency |
| Lower ODMR Transition (v0) | 229.953 | GHz | Used for MW1 detection pulse |
| Upper ODMR Transition | 235.687 | GHz | Observed transition frequency |
| Longitudinal Relaxation Time (T1) | 3.9 ± 0.2 | ms | Measured for ensemble NV centers (Sample 1) |
| Rabi π Pulse Length | 1.9 | µs | Used for spin manipulation (MW1) |
| HTA Pulse Length (MW2) | 500 | µs | Used for population transfer in EDNMR |
| Detected Bath Spins | 13C, 14N | N/A | Nuclear bath spins in the diamond lattice |
| Nearest Neighbor 13C Hyperfine Coupling | 129 | MHz | Consistent with EDNMR signals at ±65 MHz |
| P1 Center Concentration (Estimated) | ~70 | ppm | Primary source of linewidth broadening (Δω ~ 3.2 MHz) |
| Sample 1 Dimensions | 2.0 x 2.0 x 0.3 | mm3 | (111)-cut HPHT Type Ib diamond |
Key Methodologies
Section titled “Key Methodologies”The experiment relied on precise material engineering and advanced high-frequency microwave spectroscopy techniques:
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Material Selection and Preparation:
- Used (111)-cut high pressure, high temperature (HPHT) Type Ib diamond samples.
- Samples were subjected to high-energy (4 MeV) electron beam irradiation with a total fluence of 1.2 x 1018 e-/cm2.
- Post-irradiation annealing was performed at 1000 °C to mobilize vacancies and form ensemble NV centers at a concentration greater than 1 ppm.
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High-Field Spectrometer Setup:
- A custom-built, high-field ODMR spectrometer was utilized, operating in the 215-240 GHz band.
- The system incorporated a 12.1 T superconducting magnet, with the magnetic field (B0) aligned with the optical axis.
- Microwave (MW) excitation was generated by a solid-state source (Virginia Diodes) and directed via quasioptics and a corrugated waveguide.
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Pulsed ODMR and T1 Measurement:
- Pulsed laser excitation (20 µs initialization, 15 µs readout) was used to optically initialize and read out the NV spin state.
- T1 relaxation time was measured by varying the duration (τ) between initialization and readout, with and without a MW π pulse.
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EDNMR Pulse Sequence:
- The EDNMR sequence involved an initialization laser pulse, followed by a High Turning Angle (HTA) MW2 pulse (v1), a MW1 π pulse (v0) fixed at the lower NV resonance, and a final laser readout pulse.
- The frequency v1 was swept relative to v0 to drive forbidden transitions involving simultaneous electron and nuclear spin flips (Δms = 1, ΔmI = 1).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research highlights a critical need for ultra-high purity, isotopically controlled diamond materials to maximize spectral resolution and sensitivity in high-field NV-detected NMR. 6CCVD is uniquely positioned to supply the necessary SCD substrates to advance this research.
| Research Requirement | 6CCVD Material Solution | Customization Potential & Technical Advantage |
|---|---|---|
| Ultra-High Purity & Linewidth Reduction (Need to minimize P1 centers/N concentration) | Optical Grade Single Crystal Diamond (SCD) | 6CCVD provides SCD with nitrogen concentrations typically < 1 ppb, drastically reducing the P1 center concentration (~70 ppm used in the paper) that limits the EDNMR linewidth (Δω). |
| Isotopic Engineering for Resolution (Need to reduce natural abundance 13C) | Isotopically Purified SCD | We offer SCD with controlled 13C abundance (e.g., < 0.1%). This minimizes dipolar broadening from the 13C bath, enabling T2 extension and superior spectral resolution for detecting external spins. |
| Surface Sensing Capability (Need shallow NVs, > 8 nm depth, for 1H/19F detection) | Custom Thin SCD Layers & Polishing | We supply SCD wafers with precise thickness control (down to 0.1 µm) and exceptional surface quality (Ra < 1 nm). These substrates are ideal for subsequent precise shallow implantation and surface functionalization techniques. |
| Custom Dimensions for Integration (Used non-standard 2x2 mm2 and 4x4 mm2 plates) | Precision Cutting and Custom Dimensions | 6CCVD provides custom laser cutting services to meet exact experimental requirements, delivering plates and wafers up to 125 mm (PCD) or custom SCD plates up to 500 µm thick, ensuring compatibility with specialized high-field magnet systems. |
| Integrated Microwave Circuitry (Required for high-frequency MW delivery) | In-House Metalization Services | We offer custom metalization (Au, Pt, Pd, Ti, W, Cu) directly onto the diamond surface, facilitating the integration of high-frequency microwave transmission lines and antennas necessary for generating the 230 GHz MW pulses. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in optimizing diamond material properties for quantum sensing and high-frequency ESR applications. We can assist researchers in selecting the optimal SCD growth parameters (e.g., orientation, nitrogen doping, isotopic purity) required to replicate or extend this high-field NV-detected EDNMR research, particularly for projects targeting external 1H and 19F spins.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of specialized materials worldwide.
View Original Abstract
The nitrogen-vacancy (NV) center has enabled widespread study of nanoscale nuclear magnetic resonance (NMR) spectroscopy at low magnetic fields. NMR spectroscopy at high magnetic fields significantly improves the technique’s spectral resolution, enabling clear identification of closely related chemical species. However, NV-detected NMR is typically performed using AC sensing through electron spin echo envelope modulation, a hyperfine spectroscopic technique that is not feasible at high magnetic fields. Within this paper, we have explored an NV-detected NMR technique for applications of high field NMR. We have demonstrated optically detected magnetic resonance with the NV Larmor frequency of 230 GHz at 8.3 T, corresponding to a proton NMR frequency of 350 MHz. We also demonstrated the first measurement of electron-electron double resonance detected NMR using the NV center and successfully detected 13C nuclear bath spins. The described technique is limited by the longitudinal relaxation time (T1), not the transverse relaxation time (T2). Future applications of the method to perform nanoscale NMR of external spins at 8.3 T and even higher magnetic fields are also discussed.