Optical detection of paramagnetic defects in diamond grown by chemical vapor deposition

At a Glance

Metadata	Details
Publication Date	2021-03-24
Journal	Physical review. B./Physical review. B
Authors	Clément Pellet-Mary, Paul Huillery, M. Perdriat, Alexandre Tallaire, G. Hétet
Institutions	Université Paris Sciences et Lettres, Sorbonne Université
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Optical Detection of Paramagnetic Defects in CVD Diamond

Executive Summary

This research demonstrates a critical advancement in quantum material characterization by achieving all-optical detection of key paramagnetic defects (VH⁻ and WAR1) in high-purity MPCVD diamond using the Nitrogen-Vacancy (NV⁻) center as an internal sensor.

Core Achievement: Successful optical detection of hydrogen-related complexes (VH⁻) and unknown defects (WAR1) in CVD diamond via resonant cross-relaxation (CR) with a high-density NV⁻ ensemble.
Methodology: Confocal laser microscopy combined with precise magnetic field scanning (B || [100] axis) to monitor NV photoluminescence (PL) drops corresponding to CR events.
Material Requirement: High-quality, high-purity Single Crystal Diamond (SCD) grown via CVD, requiring controlled nitrogen doping (500 ppm N₂O) and post-growth high-energy electron irradiation (10 MeV) and annealing (900 °C) to optimize NV concentration (3-5 ppm).
Precision: Achieved high accuracy in determining the Zero-Field Splitting (ZFS) parameters (D) for VH⁻ (2694(5) MHz) and WAR1 (2470(10) MHz), offering a factor of 6 improvement over previous measurements.
Quantum Relevance: The ability to optically detect and hyper-polarize these defects opens pathways for employing them as novel quantum bits (qubits) and enhances the magnetic sensing capabilities of NV centers.
6CCVD Value Proposition: 6CCVD specializes in providing the necessary high-purity, custom-doped SCD substrates and post-processing consultation required to replicate and extend this foundational quantum research.

Technical Specifications

The following hard data points were extracted from the analysis of the CVD diamond material and experimental parameters:

Parameter	Value	Unit	Context
Diamond Growth Method	MPCVD	N/A	Used for high-purity material
Nitrogen Doping (N₂O)	500	ppm	Added to H₂/CH₄ (96/4) gas phase
Target NV Concentration	3 to 5	ppm	Required for high-density ensemble
Electron Irradiation Energy	10	MeV	Post-growth treatment for vacancy creation
Electron Irradiation Fluence	2 x 10¹⁸	cm^-2	Post-growth treatment
Annealing Temperature	900	°C	Post-irradiation treatment
NV⁻ Zero-Field Splitting (D)	2870	MHz	Ground state ZFS (2π * 2.87 GHz)
VH⁻ Zero-Field Splitting (D)	2694(5)	MHz	Detected hydrogen-related complex
WAR1 Zero-Field Splitting (D)	2470(10)	MHz	Detected unknown defect
Magnetic Field Scan Direction	[100]	Crystalline Axis	Used to maximize NV degeneracy
Magnetic Field Range (CR)	15 to 145	G	Range for cross-relaxation detection
Confocal Laser Power	1	mW	Green laser excitation
Objective Numerical Aperture (NA)	0.25	N/A	Used for focusing and PL collection

Key Methodologies

The experiment relied on precise material engineering and advanced optical spectroscopy techniques:

CVD Growth and Doping: Diamond was grown using the Chemical Vapor Deposition (CVD) method. Nitrogen doping was introduced by adding 500 ppm of N₂O to the H₂/CH₄ (96/4) gas mixture to achieve the required NV precursor concentration.
NV Center Creation: Post-growth processing involved high-energy (10 MeV) electron irradiation at a fluence of 2 x 10¹⁸ cm^-2 to create vacancies, followed by annealing at 900 °C to mobilize vacancies and form the negatively charged NV⁻ centers.
Confocal Microscopy Setup: A homebuilt confocal microscope was used, featuring a 1 mW green laser and a low NA (0.25) objective for focusing and photoluminescence (PL) collection.
Magnetic Field Control: Magnetic field scans were performed using a C-shaped electromagnet driven by a current generator. The field was precisely aligned along the diamond’s [100] crystalline direction using a dual-axis goniometer (Thorlabs GNL20-Z8).
Cross-Relaxation (CR) Detection: NV PL was monitored synchronously with the magnetic field changes. Drops in the normalized PL signal were observed at specific magnetic field amplitudes (20 G, 56 G, 122 G), indicating resonant energy transfer (CR) between the polarized NV⁻ spins and the target paramagnetic defects (VH⁻, WAR1, ¹³C-NV pairs).
Data Analysis: A 4^th-order polynomial fit was subtracted from the raw PL data to isolate the narrow CR features, allowing for precise determination of the defect Zero-Field Splitting (D) parameters.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and engineering services required to replicate and extend this critical quantum research.

Applicable Materials

To achieve the high purity, controlled doping, and high NV density demonstrated in this paper, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for high-fidelity quantum experiments. Our SCD material ensures low strain and minimal background impurities, crucial for achieving the long coherence times (T₂) necessary for sensitive CR detection.
Custom Nitrogen Doped SCD: We offer precise control over nitrogen incorporation during the MPCVD growth process, enabling researchers to target the 3-5 ppm NV concentration range specified in the paper via controlled N₂O doping.
Isotopically Purified ¹²C SCD: While the paper notes the benefit of ¹²C enrichment for removing ¹³C spin fluctuations, 6CCVD can supply isotopically purified SCD (e.g., < 1% ¹³C) to further enhance the sensing capabilities and coherence time of the NV centers.

Customization Potential

The success of this experiment hinges on precise material geometry and orientation. 6CCVD offers full customization capabilities:

Research Requirement	6CCVD Custom Capability	Benefit to Researcher
Crystal Orientation	Custom orientation cuts (e.g., [100], [111])	Enables precise alignment of the magnetic field (B) relative to the NV axis for specific CR studies.
Polishing	SCD Polishing to Ra < 1 nm	Ensures optimal optical access and minimal scattering losses for confocal microscopy and PL collection.
Dimensions	Custom plates/wafers up to 125 mm (PCD)	While SCD is preferred here, we offer large-area PCD for scaling up quantum device fabrication. SCD thickness available from 0.1 µm to 500 µm.
Post-Processing Consultation	Assistance with high-energy irradiation and annealing protocols (10 MeV, 900 °C)	Our PhD engineering team can advise on optimal post-growth treatments to maximize NV yield and control defect formation (VH⁻, WAR1).
Device Integration	Custom Metalization (Au, Pt, Pd, Ti, W, Cu)	Although not used for detection here, future quantum devices based on these coupled spins will require electrodes. We offer in-house metalization services for device integration.

Engineering Support

6CCVD’s in-house PhD team provides expert engineering support for material selection and optimization for similar NV-based Quantum Sensing and Defect Spectroscopy projects. We ensure that the material properties—including purity, doping profile, and surface finish—are optimized for demanding quantum applications requiring long coherence times and high spin contrast.

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

View Original Abstract

The electronic spins of the nitrogen-vacancy centers (NV centers) in\nChemical-Vapor-Deposition (CVD) grown diamonds form ideal probes of magnetic\nfields and temperature, as well as promising qu-bits for quantum information\nprocessing. Studying and controlling the magnetic environment of NV centers in\nsuch high purity crystals is thus essential for these applications. We\ndemonstrate optical detection of paramagnetic species, such as hydrogen-related\ncomplexes, in a CVD-grown diamond. The resonant transfer of the NV centers’\npolarized electronic spins to the electronic spins of these species generates\nconspicuous features in the NV photoluminescence by employing magnetic field\nscans along the [100] crystal direction. Our results offer prospects for more\ndetailed studies of CVD-grown processes as well as for coherent control of the\nspin of novel classes of hyper-polarized paramagnetic species.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.103.l100411