Universal Dependence of Nuclear Spin Relaxation on the Concentration of Paramagnetic Centers in Nano- and Microdiamonds

At a Glance

Metadata	Details
Publication Date	2022-08-21
Journal	Materials
Authors	A. M. Panich
Institutions	Ben-Gurion University of the Negev
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nuclear Spin Relaxation in Diamond

Reference: Panich, A.M. Universal Dependence of Nuclear Spin Relaxation on the Concentration of Paramagnetic Centers in Nano- and Microdiamonds. Materials 2022, 15, 5774.

Executive Summary

This research establishes a fundamental, universal relationship between nuclear spin relaxation (T₁, T₂) and the concentration of paramagnetic centers (C) in various diamond materials, providing critical insights for advanced applications.

Universal Law Established: The study confirms that nuclear spin relaxation rates (R₁ = 1/T₁, R₂ = 1/T₂) depend linearly on the concentration of paramagnetic centers (C), while the relaxation times (T₁, T₂) exhibit a hyperbolic dependence on C.
Material Scope: This law is validated across diverse diamond forms, including purified detonation nanodiamonds (DNDs), DNDs grafted with metal ions (Gd³⁺, Cu²⁺), and powdered micro/nanodiamonds produced by milling HPHT bulk diamond (SYP series).
Paramagnetic Centers: Key centers investigated include intrinsic P1 nitrogen defects, unpaired electron spins of dangling bonds (surface defects), and grafted Gd(III) and Cu(II) ions.
Application Relevance: The findings are directly applicable to optimizing diamond materials for high-impact fields, including quantum computing (NV centers), spintronics, nanophotonics, and biomedical Magnetic Resonance Imaging (MRI) contrast agents.
Defect Engineering Necessity: The research underscores the critical need for precise control over paramagnetic defect concentration and surface functionalization to achieve predictable relaxation behavior in solid-state and suspension applications.

Technical Specifications

The following hard data points were extracted from the analysis of the diamond materials and NMR measurements:

Parameter	Value	Unit	Context
Average DND Particle Size	4.5 - 5	nm	Determined by DLS, TEM, and AFM
Milled HPHT ND Particle Size Range (SYP)	18 to 386	nm	Various fractions used in the study
Total Intrinsic Paramagnetic Defect Density (DND)	(4 - 7) x 10¹⁹	spin/g	Measured by EPR in purified DNDs
Paramagnetic Defect Density (SYP NDs)	6.7 x 10¹⁸ to 3.3 x 10¹⁹	spin/g	Varies inversely with particle size
¹H NMR Resonance Frequency	340.52	MHz	Corresponding to B₀ = 8.0 T
¹³C NMR Resonance Frequency	85.62	MHz	Corresponding to B₀ = 8.0 T
Powder Sample Measurement Temperature	295	K	Solid-state NMR measurements
Suspension Measurement Temperature	310.1 (37)	K (°C)	Relevant for biomedical/MRI studies
Gd(III) Magnetic Moment	7.9	µ_B	Large unpaired electron spin S = 7/2

Key Methodologies

The study utilized a combination of material synthesis, surface modification, and advanced magnetic resonance techniques to characterize the spin relaxation phenomena:

Material Sourcing and Preparation: Detonation nanodiamonds (DNDs) and micro/nanodiamonds produced by milling initial High-Temperature High-Pressure (HTHP) microdiamond crystallites (SYP series) were used.
Purification and Impurity Control: Samples underwent rigorous purification to exclude ferro- and paramagnetic impurities, monitored via Electron Paramagnetic Resonance (EPR) and SQUID techniques.
Surface Grafting: Paramagnetic ions (Cu²⁺ and Gd³⁺) were chemically grafted onto the DND surface via ion exchange with hydrogen atoms of surface carboxyl groups, creating Cu-DND and Gd-DND.
Physical Characterization: Particle size was determined using Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM).
NMR Spectroscopy: ¹H and ¹³C NMR measurements were performed on both powder samples (solid-state) and aqueous suspensions (liquid-state) at a high magnetic field (8.0 T).
T₁ Measurement: Spin-lattice relaxation times (T₁) were measured using inversion recovery (¹H) or a saturation comb pulse sequence (¹³C). Magnetization recovery was fitted using a stretched exponential function, characteristic of paramagnetic defect relaxation.
T₂ Measurement: Spin-spin relaxation times (T₂) were measured using the Carr-Purcell-Meiboom-Gill (CPMG) sequence (¹H) or the Hahn echo method (¹³C).

6CCVD Solutions & Capabilities

The research highlights the critical role of controlled paramagnetic centers and material purity in enabling advanced diamond applications. While the paper focuses on nanodiamond powders, 6CCVD specializes in high-quality, large-area MPCVD diamond wafers (SCD and PCD), offering superior platforms for integrated quantum, spintronic, and nanophotonic devices.

Applicable Materials for Advanced Research

To replicate or extend this research into integrated solid-state devices, 6CCVD recommends materials engineered for precise defect control and high purity:

6CCVD Material	Application Focus	Key Advantage over Powder
High Purity Single Crystal Diamond (SCD)	Quantum Computing, Spintronics	Ultra-low intrinsic defect density (P1 centers) allows for precise, controlled creation of NV centers via ion implantation or tailored MPCVD growth, minimizing background noise.
Optical Grade SCD	Nanophotonics, Integrated Optics	High transmission and low birefringence, ideal for integrating NV centers into waveguides and photonic structures.
Boron-Doped Diamond (BDD)	Electrochemical Sensing, MRI Relaxivity Studies	Tunable conductivity and robust surface chemistry, providing a stable platform for studying grafted paramagnetic ions and electrochemical spin dynamics.
Large-Area Polycrystalline Diamond (PCD)	MRI Phantoms, High-Power Electronics	Available in plates up to 125mm, offering uniform, large-scale substrates for developing MRI phantoms or high-thermal-conductivity components.

Customization Potential for Device Integration

The transition from powder-based research to functional devices requires precise material engineering and integration capabilities, which 6CCVD provides:

Custom Dimensions and Thickness: Unlike milled powders, 6CCVD offers MPCVD diamond plates and wafers with highly controlled dimensions.
- SCD Thickness: From 0.1µm (thin films for membranes) up to 500µm.
- PCD Dimensions: Wafers up to 125mm in diameter.
- Substrates: Bulk substrates up to 10mm thick.
Precision Polishing: Achieving ultra-smooth surfaces is critical for minimizing surface dangling bonds (a source of paramagnetic defects identified in the paper) and enabling high-fidelity device fabrication.
- SCD Polishing: Surface roughness (Ra) < 1nm.
- PCD Polishing: Surface roughness (Ra) < 5nm (for inch-size wafers).
Custom Metalization Services: For integrating diamond into spintronic or sensor architectures, 6CCVD provides in-house deposition of standard and specialized metals, including Au, Pt, Pd, Ti, W, and Cu. This capability is essential for creating reliable electrical contacts and surface functionalization layers.

Engineering Support & Defect Control

The universal law demonstrated in this paper confirms that precise control over paramagnetic center concentration is paramount. 6CCVD’s expertise in MPCVD growth offers a superior method for defect engineering compared to the mechanical milling used to create the SYP nanodiamonds:

Controlled Nitrogen Incorporation: Our in-house PhD team can precisely control the nitrogen concentration during MPCVD growth, allowing researchers to tailor the density of P1 centers (NV precursors) for optimal quantum sensing performance.
Material Selection Consultation: We provide expert consultation to assist engineers and scientists in selecting the optimal diamond grade, thickness, and orientation required to meet the specific T₁ and T₂ relaxation targets for their quantum computing, spintronics, or biomedical projects.
Global Logistics: We ensure reliable, global delivery of custom diamond materials, with DDU (Delivered Duty Unpaid) as the default and DDP (Delivered Duty Paid) available upon request.

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

View Original Abstract

An analysis of our data on 1H and 13C spin-lattice and spin-spin relaxation times and rates in aqueous suspensions of purified nanodiamonds produced by detonation technique (DNDs), DNDs with grafted paramagnetic ions, and micro- and nanodiamonds produced by milling bulk high-temperature high-pressure diamonds is presented. It has been established that in all the studied materials, the relaxation rates depend linearly on the concentration of diamond particles in suspensions, the concentration of grafted paramagnetic ions, and surface paramagnetic defects produced by milling, while the relaxation times exhibit a hyperbolic dependence on the concentration of paramagnetic centers. This is a universal law that is valid for suspensions, gels, and solids. The results obtained will expand the understanding of the properties of nano- and microdiamonds and will be useful for their application in quantum computing, spintronics, nanophotonics, and biomedicine.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15165774

References

2015 - Science and engineering of nanodiamond particle surfaces for biological applications (Review) [Crossref]
2018 - Fluorescent Single-Digit Detonation Nanodiamond for Biomedical Applications [Crossref]
2006 - Processing Quantum Information in Diamond [Crossref]
2013 - The Nitrogen-Vacancy Color Centre in Diamond [Crossref]
2019 - Review Article: Synthesis, Properties, and Applications of Fluorescent Diamond Particles [Crossref]
2014 - Diamond Nanophotonics [Crossref]
2021 - Background-Free Dual-Mode Optical and 13C Magnetic Resonance Imaging in Diamond Particles [Crossref]
2019 - High Temperature Treatment of Diamond Particles Toward Enhancement of Their Quantum Properties [Crossref]