Optimization of the coherence properties of diamond samples with an intermediate concentration of NV centers

At a Glance

Metadata	Details
Publication Date	2021-01-19
Journal	Results in Physics
Authors	O. R. Rubinas, V.V. Soshenko, S. V. Bolshedvorskii, A. I. Zeleneev, A.S. Galkin
Institutions	Texas A&M University, Technological Institute for Superhard and Novel Carbon Materials
Citations	15
Analysis	Full AI Review Included

Technical Documentation & Analysis: Optimization of NV Center Coherence

This document analyzes the research paper, “Optimization of the coherence properties of diamond samples with an intermediate concentration of NV centers,” and outlines how 6CCVD’s advanced MPCVD diamond materials and processing capabilities can meet and exceed the requirements for high-sensitivity quantum sensing applications.

Executive Summary

This research successfully demonstrates a methodology for optimizing the coherence properties of Nitrogen-Vacancy (NV) center ensembles in diamond, crucial for high-sensitivity magnetometry.

Core Challenge Addressed: Compensating for the increased decoherence rate ($T_{2}^{*}$ decrease) that typically accompanies higher substitutional nitrogen donor ($P_1$) concentrations necessary for high NV ensemble density.
Material Focus: Investigation of diamond plates with intermediate nitrogen concentrations ($10^{17} - 10^{18}$ cm⁻³, or 0.6 - 5.6 ppm).
Key Optimization: Efficient conversion of substitutional nitrogen donors into NV centers (specifically the useful $NV^{-}$ state) via optimized electron irradiation and annealing post-processing.
Optimal Parameters: An electron irradiation dose of approximately $15 \cdot 10^{17}$ cm⁻² (at 3 MeV) followed by 800 °C annealing was found to be optimal.
Performance Achievement: The optimized process yielded a dephasing time ($T_{2}^{*}$) of 0.7 µs, closely approaching the theoretical ¹³C decoherence limit (0.9 µs).
Sensitivity Gain: This post-processing optimization resulted in an approximately 2 times improvement in potential sensor sensitivity compared to non-optimal procedures.

Technical Specifications

The following hard data points were extracted from the research paper, detailing the material properties and experimental results.

Parameter	Value	Unit	Context
Nitrogen Concentration Range ($P_1$)	$10^{17} - 10^{18}$	cm⁻³	Intermediate range investigated (0.6 - 5.6 ppm)
Optimal Electron Irradiation Dose	$15 \cdot 10^{17}$	cm⁻²	Optimal dose for NV center fraction saturation
Electron Energy	3	MeV	Used for vacancy creation
Annealing Temperature	800	°C	Post-irradiation thermal treatment
Maximum Dephasing Time ($T_{2}^{*}$)	0.7	µs	Achieved at optimal dose (15V sample)
Maximum Coherence Time ($T_2$)	179.88	µs	Achieved at $4 \cdot 10^{17}$ cm⁻² dose
Target Decoherence Limit (¹³C)	0.9	µs	Theoretical limit for natural abundance diamond
NV⁻ Concentration (Optimal Dose)	$44.9 \pm 2.8$	ppb	Concentration at $15 \cdot 10^{17}$ cm⁻² dose
NV⁰ Concentration (Optimal Dose)	$273.1 \pm 7.9$	ppb	Concentration at $15 \cdot 10^{17}$ cm⁻² dose
Sensitivity Improvement	2	times	Compared to non-optimal post-processing

Key Methodologies

The experiment relied on precise material preparation and advanced quantum characterization techniques to achieve optimal NV center coherence.

Diamond Growth: Diamond plates were grown using the High-Pressure High-Temperature (HPHT) technique, focusing on low strain characteristics.
Vacancy Creation: Samples were subjected to high-energy electron beam irradiation (3 MeV) across a wide dose range ($2\cdot10^{17}$ to $20\cdot10^{17}$ cm⁻²) to generate vacancies.
NV Conversion: Post-irradiation annealing was performed at 800 °C to mobilize vacancies, facilitating their capture by substitutional nitrogen donors ($P_1$) to form NV centers.
Substitutional Nitrogen Measurement: Concentration of $P_1$ centers was determined using continuous wave Electron Paramagnetic Resonance (CW-EPR) spectroscopy, normalized against a known calibration sample.
NV Charge State Measurement: Concentrations of $NV^{-}$ (637 nm peak) and $NV^{0}$ (575 nm peak) were measured via optical transmission spectroscopy at cryogenic temperature (-77 K).
Dephasing Time ($T_{2}^{*}$) Measurement: Measured via the fitting decay of Ramsey fringes, implemented using a $\pi/2-\tau-\pi/2$ microwave and optical pulse sequence.
Coherence Time ($T_2$) Measurement: Measured using the Hahn echo sequence ($\pi/2-\tau-\pi-\tau-\pi/2$) under a high magnetic field (80 Gauss) to decouple the NV ensemble from the ¹³C spin bath.

6CCVD Solutions & Capabilities

6CCVD specializes in providing high-purity, low-strain MPCVD diamond, offering superior control over nitrogen incorporation and crystal quality compared to the HPHT material used in this study. Our capabilities are perfectly suited to replicate, refine, and scale this high-coherence NV ensemble research.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials, optimized for quantum sensing:

Optical Grade Single Crystal Diamond (SCD): Our SCD material is grown via MPCVD, offering extremely low strain and high purity, which is critical for achieving long intrinsic coherence times.
- Controlled Nitrogen Doping: We offer precise, controlled nitrogen incorporation during growth, allowing researchers to target the exact intermediate concentration range ($10^{17} - 10^{18}$ cm⁻³) investigated in this paper, ensuring uniform $P_1$ distribution.
Isotopically Pure Diamond (Optional Extension): For research aiming to surpass the 0.9 µs ¹³C decoherence limit, 6CCVD can supply SCD grown with depleted ¹²C precursors, enabling $T_2$ times significantly longer than those reported here.

Customization Potential

The success of this research hinges on precise material dimensions and post-processing readiness. 6CCVD provides comprehensive customization services:

Requirement from Paper	6CCVD Capability	Benefit to Researcher
Custom Dimensions	Plates/wafers up to 125mm (PCD) and custom SCD sizes.	Enables scaling from research samples to large-area sensor arrays.
Thickness Control	SCD thickness from 0.1 µm to 500 µm.	Allows optimization of NV layer depth and total active volume for specific sensing geometries (e.g., shallow NV for surface sensing).
Post-Processing Readiness	Low-strain, high-purity material optimized for subsequent electron irradiation and high-temperature annealing (800 °C).	Ensures maximum conversion efficiency of $P_1$ centers to $NV^{-}$ centers without introducing new defects.
Advanced Integration	Internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu).	Allows for direct integration of microwave antennas (as used in Figure 3B) and electrical contacts onto the diamond surface for ODMR experiments.
Polishing	SCD polishing to Ra < 1 nm.	Essential for minimizing surface scattering losses and ensuring high-efficiency optical collection required for magnetometry.

Engineering Support

6CCVD’s in-house PhD team specializes in defect engineering and material science for quantum applications. We offer consultation services to assist researchers in:

Material Selection: Determining the optimal nitrogen concentration and growth parameters to achieve specific $T_{2}^{*}$ and $NV^{-}$ concentration targets for DC Magnetometry and Quantum Sensing projects.
Post-Processing Optimization: Advising on the necessary pre- and post-growth treatments (including irradiation and annealing protocols) to maximize the yield of the desired $NV^{-}$ charge state.
Integration Design: Supporting the design and implementation of custom metalization patterns for microwave delivery and signal readout.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.rinp.2021.103845

References

2013 - Nanoscale magnetometry with NV centers in diamond [Crossref]
2012 - Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array [Crossref]
2008 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
2018 - Spin properties of NV centers in high-pressure, high-temperature grown diamond [Crossref]
2009 - Diamonds with a high density of nitrogen-vacancy centers for magnetometry applications [Crossref]
2018 - Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control
2014 - Statistical investigations on nitrogen-vacancy center creation [Crossref]
2016 - Electron spin decoherence of nitrogen-vacancy center coupled to multiple spin baths [Crossref]
2011 - Magnetic field imaging with nitrogen-vacancy ensembles [Crossref]