Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond

At a Glance

Metadata	Details
Publication Date	2015-12-14
Journal	Applied Physics Letters
Authors	Andrey Jarmola, Andris Bērziņš, Jānis Šmits, Krišjānis Šmits, Juris Prikulis
Institutions	University of Latvia, Johannes Gutenberg University Mainz
Citations	48
Analysis	Full AI Review Included

Technical Documentation & Analysis: Longitudinal Spin-Relaxation in NV Centers

This document analyzes the research paper “Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond” and outlines how 6CCVD’s advanced MPCVD diamond materials and fabrication capabilities can support, replicate, and extend this critical quantum research.

Executive Summary

Core Achievement: Systematic measurement of the longitudinal spin relaxation rate (1/T₁) of NV⁻ centers in synthetic diamond as a function of concentration and magnetic field (B).
Material & Method: NV⁻ centers were generated in a Type 1b single-crystal diamond (3x3x0.3 mm) via 200 keV electron irradiation (TEM) along the [100] axis, followed by 800 °C annealing.
Concentration Range: Measurements were performed across 17 distinct spots, achieving an NV⁻ concentration range spanning an order of magnitude (0.2 ppm to 7.1 ppm).
Key Finding (Relaxation): The relaxation rate (1/T₁) showed a strong, nearly linear dependence on NV⁻ concentration, increasing by a factor of five across the tested range.
Key Finding (Purity): Lower NV⁻ concentrations resulted in a better-defined relaxation rate (stretched exponential parameter β approaching unity), indicating reduced interaction with nearby spins.
Application Relevance: The methodology validates TEM irradiation for creating microscale NV structures, guiding the preparation of high-performance NV sensors for quantum information and magnetometry.
6CCVD Value Proposition: 6CCVD provides superior, low-strain, custom-doped Single Crystal Diamond (SCD) substrates necessary for achieving the highest quality NV⁻ ensembles and single-spin devices.

Technical Specifications

The following hard data points were extracted from the experimental setup and results:

Parameter	Value	Unit	Context
Base Material Type	Type 1b (HPHT)	N/A	Single-crystal diamond plate
Initial Nitrogen Concentration	200	ppm	Starting material impurity level
Sample Dimensions	3 x 3 x 0.3	mm	[100] cut orientation
Thickness	300	µm	Sample thickness
Electron Accelerating Voltage	200	kV	TEM irradiation source
Effective Vacancy Creation Depth	~20	µm	Estimated depth for NV formation
Annealing Temperature	800	°C	Post-irradiation thermal treatment
Annealing Time	3	hours	In nitrogen gas (N₂)
NV⁻ Concentration Range (Estimated)	0.2 to 7.1	ppm	Achieved via varying electron doses
Electron Dose Range	1.1 x 10¹⁹ to 2.5 x 10²¹	cm^-2	Used to create varying NV⁻ spots
Excitation Wavelength	512	nm	External cavity diode laser
Zero-Field Splitting (D)	~2.87	GHz	NV ground state resonance frequency
Maximum Strain Splitting (2E)	~6	MHz	Observed at highest NV concentration
Relaxation Rate Increase (Factor)	~5	N/A	Increase in 1/T₁ across concentration range

Key Methodologies

The experiment relied on precise material preparation and advanced optical/microwave control for Optically Detected Magnetic Resonance (ODMR) measurements.

Material Selection: A [100] cut Type 1b single-crystal diamond (3mm x 3mm x 0.3 mm) with 200 ppm initial nitrogen concentration was selected.
Irradiation: The sample was irradiated along the [100] axis using a Transmission Electron Microscope (TEM) at 200 kV. Seventeen circular spots (10 µm diameter) were created using varying electron doses to control the resulting NV concentration.
Annealing: The sample was annealed at 800 °C for three hours in a nitrogen gas atmosphere to mobilize vacancies and form NV⁻ centers.
Magnetic Field Alignment: A three-axis Helmholtz coil system was used to align the magnetic field (B) along the [111] crystallographic direction.
Spin Polarization: NV centers were pumped into the m_s = 0 ground state using a 50 µs green laser pulse (512 nm).
Longitudinal Relaxation Measurement (T₁): T₁ was measured using a pump-probe sequence: pump pulse, variable dark time (τ), followed by fluorescence readout. The decay curve was fit using a stretched exponential function, exp [-(τ/T₁)^β].
Microwave Delivery: Microwaves (MW) were delivered via a 0.071 mm copper wire placed close to the diamond surface, terminated into 50 Ω.

6CCVD Solutions & Capabilities

This research demonstrates the critical need for high-quality, precisely engineered diamond substrates for quantum applications. 6CCVD’s MPCVD capabilities offer significant advantages over the HPHT Type 1b material used in this study, enabling higher performance and scalability for microscale NV sensors.

Applicable Materials

To replicate and advance this research, 6CCVD recommends the following materials:

Material Grade	Application Focus	6CCVD Advantage
Quantum Grade SCD	Low-strain, high-coherence NV⁻ centers (single-spin or low-ensemble).	Ultra-low intrinsic nitrogen (N < 1 ppb) for superior T₂ coherence times, ideal for creating NV centers via external implantation/irradiation.
Custom N-Doped SCD	Controlled ensemble NV⁻ centers (as used in this paper).	Precise, in-situ nitrogen doping during MPCVD growth, allowing for specific, uniform N concentrations (e.g., 0.5 ppm to 10 ppm) far superior to the high, uncontrolled 200 ppm of Type 1b.
Optical Grade SCD	Minimizing scattering losses for high-NA optical collection.	High transparency and low birefringence, critical for maximizing fluorescence collection efficiency.

Customization Potential

6CCVD’s advanced fabrication services directly address the requirements for microscale quantum device preparation:

Custom Dimensions and Thickness: The paper used a 300 µm thick, 3x3 mm sample. 6CCVD routinely supplies SCD wafers up to 500 µm thick and PCD plates up to 125 mm in custom geometries, ensuring scalability for industrial sensor development.
Ultra-Low Roughness Polishing: Achieving high-fidelity optical coupling requires exceptional surface quality. 6CCVD guarantees Ra < 1 nm for Single Crystal Diamond (SCD) surfaces, minimizing scattering and maximizing signal-to-noise ratio in ODMR experiments.
Integrated Metalization Services: While the paper used a simple external copper wire for MW delivery, advanced NV experiments require integrated microwave structures (e.g., coplanar waveguides). 6CCVD offers in-house custom metalization using materials including Au, Pt, Pd, Ti, W, and Cu, directly patterned onto the diamond surface.
Substrate Preparation: 6CCVD can supply substrates pre-cut and polished to specific crystallographic orientations ([100], [111], etc.), ready for immediate electron irradiation or ion implantation processes.

Engineering Support

The relationship between NV concentration, strain (2E), and relaxation time (1/T₁) is complex. 6CCVD’s in-house PhD team specializes in optimizing diamond material parameters (initial N concentration, crystal orientation, and surface termination) for similar NV-based Quantum Sensing and Magnetometry projects. We provide consultation to ensure the starting material is perfectly matched to the desired NV density and coherence requirements.

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

View Original Abstract

We present systematic measurements of longitudinal relaxation rates (1/T1) of spin polarization in the ground state of the nitrogen-vacancy (NV-) color center in synthetic diamond as a function of NV- concentration and magnetic field B. NV- centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV- center concentrations. Values of (1/T1) were measured for each spot as a function of B.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4937489