Demonstration of NV-detected ESR spectroscopy at 115 GHz and 4.2 T

At a Glance

Metadata	Details
Publication Date	2020-04-27
Journal	Applied Physics Letters
Authors	Benjamin Fortman, Junior Peña, Karoly Holczer, Susumu Takahashi, Benjamin Fortman
Institutions	University of Southern California
Citations	15
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Frequency NV-Detected ESR

Executive Summary

This research demonstrates a significant advancement in high-field quantum sensing by successfully implementing Nitrogen-Vacancy (NV) detected Electron Spin Resonance (ESR) spectroscopy at 115 GHz and 4.2 Tesla. This breakthrough provides a critical foundation for high-resolution nanoscale magnetic sensing.

High-Field Quantum Sensing: NV-ESR was successfully demonstrated at a high Larmor frequency (115 GHz) and corresponding magnetic field (4.2 Tesla), overcoming limitations associated with spectral overlap at low fields.
Nanoscale Detection: The technique utilized NV centers in diamond to detect single-substitutional nitrogen (P1) centers, proving the capability for nanoscale characterization of external spins.
Enhanced Coherent Control: The application of linear frequency-swept chirp pulses achieved near 100% population inversion of the NV spin state, drastically improving signal-to-noise ratio and excitation bandwidth compared to conventional rectangular pulses.
Methodology: The experiment employed a Double Electron-Electron Resonance (DEER) sequence on both ensemble and single NV systems.
Material Requirement: The study relied on high-quality, (111)-cut Type-Ib diamond substrates optimized via 4 MeV electron irradiation and 1000 °C annealing to achieve an optimal NV/N ratio (~8%).
Future Applications: This work paves the way for high-resolution High-Frequency (HF) NV-detected Nuclear Magnetic Resonance (NMR) spectroscopy, enabling structural and dynamic studies of biomacromolecules and complex solid-state interfaces.

Technical Specifications

The following hard data points were extracted from the research paper, highlighting the critical operational parameters and material performance metrics.

Parameter	Value	Unit	Context
NV Larmor Frequency	115	GHz	Operating frequency for NV-ESR measurement
Magnetic Field (B₀)	4.2	Tesla	Corresponding magnetic field for 115 GHz operation
Maximum Magnet Field	12.1	Tesla	Maximum capability of the superconducting magnet system
Ensemble Sample Dimensions	2.0 x 2.0 x 0.3	mm³	Size of the (111)-cut Type-Ib diamond substrate
Electron Irradiation Energy	4	MeV	Used for NV center creation
Annealing Temperature	1000	°C	Used to increase NV center density
Electron Fluence	1.2 x 10¹⁸	e-/cm²	Total exposure for ensemble NV creation
NV/N Ratio (Resulting)	~8	%	Ratio achieved after irradiation and annealing
Ensemble T₂ (Decoherence Time)	2.4 ± 0.3	µs	Measured using spin echo decay (without chirp pulses)
Single NV T₂ (Estimated)	~20	µs	Measured using spin echo (with chirp pulses)
Chirp Pulse Efficiency	~100	%	Estimated population inversion achieved
Future Extension Frequency	230	GHz	Target frequency for higher spectral resolution (8.2 Tesla)

Key Methodologies

The successful demonstration of HF NV-ESR relied on precise material preparation and advanced microwave control techniques.

Material Selection and Preparation:
- (111)-cut Type-Ib diamond substrates were utilized to align the NV axis with the high magnetic field.
- Ensemble samples were subjected to high-energy (4 MeV) electron beam irradiation and subsequent high-temperature annealing (1000 °C) to control and maximize the NV center density relative to P1 centers.
System Integration:
- A custom High-Frequency (HF) Optically Detected Magnetic Resonance (ODMR) system was built, incorporating a 12.1 Tesla cryogenic-free superconducting magnet and quasioptical microwave propagation for low-loss, broadband transmission.
Spin Characterization:
- Initial characterization of the NV centers included pulsed ODMR, Rabi oscillation measurements, and spin echo sequences to determine the spin decoherence time (T₂).
Advanced Pulse Shaping:
- Linear frequency-swept chirp pulses were implemented at 115 GHz to overcome the limited excitation bandwidth of rectangular pulses, achieving near 100% population inversion and high-fidelity coherent control.
High-Resolution Spectroscopy:
- A Double Electron-Electron Resonance (DEER) sequence was employed to perform NV-ESR spectroscopy, enabling the detection of weakly coupled P1 centers in the nanometer vicinity of the NV center.

6CCVD Solutions & Capabilities

The research highlights the critical need for ultra-high-purity diamond substrates with precise crystallographic orientation and controlled defect engineering. 6CCVD is uniquely positioned to supply the next generation of materials required to replicate and extend this high-field quantum sensing research, particularly towards the 230 GHz (8.2 Tesla) target.

Applicable Materials

To achieve the long coherence times (T₂) and high spectral resolution demonstrated, 6CCVD recommends the following materials, offering superior purity and control compared to the HPHT Type-Ib used in the study:

Optical Grade Single Crystal Diamond (SCD): Our high-purity MPCVD SCD offers extremely low intrinsic nitrogen content (< 1 ppb), providing a pristine host lattice. This is essential for maximizing T₂, which is critical for high-resolution NMR/ESR applications.
Custom Nitrogen-Doped SCD: We can precisely incorporate nitrogen during the MPCVD growth process to control the concentration of P1 centers (the precursor to NV centers), allowing researchers to fine-tune the NV/P1 ratio for optimal sensing performance.

Customization Potential

The success of this high-field experiment relies on specific material geometry and defect engineering, capabilities that 6CCVD provides as standard services:

Research Requirement	6CCVD Capability	Technical Advantage for HF-ESR
Crystal Orientation	Custom (111) SCD Plates	We supply SCD plates in standard (100) or custom (111) orientation, ensuring the NV axis is optimally aligned with the high magnetic field (B₀) for maximum spectral resolution.
Custom Dimensions	Precision Laser Cutting & Polishing	We provide plates in any custom dimension (e.g., 2.0 x 2.0 x 0.3 mm³) up to 500 µm thickness for SCD, ensuring compatibility with specialized cryogenic magnet bores and quasioptical setups.
Surface Quality	Ultra-Low Roughness Polishing (Ra < 1 nm)	Essential for minimizing optical scattering and maximizing photon collection efficiency in the ODMR system, especially for single NV detection.
Defect Engineering	Post-Growth Irradiation & Annealing	We offer controlled high-energy electron irradiation and high-temperature annealing services (up to 1000 °C) to achieve the specific NV/N ratios (>8%) required for ensemble or single-spin experiments.
Microwave Integration	Custom Metalization (Au, Ti/Pt/Au)	For future integration of on-chip microwave structures (e.g., coplanar waveguides) necessary for high-power delivery at 230 GHz, 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu).

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing diamond material properties for quantum applications. We can assist researchers in designing custom substrates to meet the stringent requirements of high-frequency NV-detected NMR and ESR projects, including:

T₂ Maximization: Consulting on nitrogen concentration and isotopic purity (e.g., ¹²C enrichment) to extend spin coherence times beyond the 20 µs demonstrated.
High-Field Compatibility: Material selection and geometry optimization for integration into high-Tesla cryogenic systems.
Defect Control: Tailoring irradiation and annealing protocols to achieve optimal NV/P1 ratios for specific sensing targets (e.g., external surface spins or intracellular environments).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

High frequency electron spin resonance (ESR) spectroscopy is an invaluable tool for identification and characterization of spin systems. Nanoscale ESR using the nitrogen-vacancy (NV) center has been demonstrated down to the level of a single spin. However, NV-detected ESR has exclusively been studied at low magnetic fields, where the spectral overlap prevents clear identification of spectral features. In this work, we demonstrate NV-detected ESR measurements of single-substitutional nitrogen impurities in diamond at a NV Larmor frequency of 115 GHz and the corresponding magnetic field of 4.2 T. The NV-ESR measurements utilize a double electron-electron resonance sequence and are performed using both ensemble and single NV spin systems. In the single NV experiment, chirp pulses are used to improve the population transfer and for NV-ESR measurements. This work provides the basis for NV-based ESR measurements of external spins at high magnetic fields.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0006014