High Temperature Treatment of Diamond Particles Toward Enhancement of Their Quantum Properties

At a Glance

Metadata	Details
Publication Date	2020-06-10
Journal	Frontiers in Physics
Authors	Marco D. Torelli, Nicholas Nunn, Zachary R. Jones, Thea Vedelaar, Sandeep K. Padamati
Institutions	University of Wisconsin–Madison, College of Staten Island
Citations	15
Analysis	Full AI Review Included

6CCVD Technical Documentation: RTA Enhancement of Diamond Quantum Properties

Reference: Torelli et al. (2020). High Temperature Treatment of Diamond Particles Toward Enhancement of Their Quantum Properties. Frontiers of Physics, 8, Article 205. DOI: 10.3389/fphy.2020.00205

Executive Summary

This research demonstrates that Rapid Thermal Annealing (RTA) is a critical post-synthesis processing step for significantly enhancing the quantum properties of Nitrogen-Vacancy (NV^-) centers in diamond particles, crucial for advanced quantum sensing and bio-imaging applications.

4x Performance Improvement: RTA treatment increased the maximum achievable magnetic modulation contrast of NV fluorescence by approximately 4x (from ~5% to ~20%) compared to standard 850°C annealing.
Lattice Healing & Defect Elimination: High-temperature RTA (up to 1740°C) efficiently eliminates parasitic paramagnetic impurities, specifically negatively charged vacancies (V^-) and other triplet defects, leading to improved NV performance.
Optimized Recipe: The highest magnetic modulation contrast was achieved using a short-duration, high-temperature RTA recipe (1740°C for 8 minutes).
Multicolor Sensing Capability: RTA treatment simultaneously increases the concentration of H3 centers (NVN), providing a stable, non-modulated reference peak (420 nm excitation) for self-calibration in environments with rapidly changing fluorescent backgrounds.
Application Focus: The enhanced magnetic modulation contrast enables high-fidelity, background-free imaging and sensing, particularly relevant for intracellular probes and hyperpolarization agents in complex biological matrices.

Technical Specifications

The following hard data points were extracted from the study detailing the material processing and resulting quantum performance metrics.

Parameter	Value	Unit	Context
Starting Material Type	Type Ib HPHT	N/A	Diamond particles
Initial Substitutional Nitrogen (P1)	~110	ppm	Pre-irradiation concentration
Particle Sizes Tested	20, 140	µm, nm	Micro- and Nanodiamonds
Electron Irradiation Fluence	1.5 x 10¹⁹	e/cm²	Used 3 MeV high-energy electrons
Standard Annealing Condition	850°C / 2	°C / h	Control sample for NV formation
Optimal RTA Condition (Modulation)	1740°C / 8	°C / min	Achieved highest magnetic contrast
RTA Temperature Range Tested	1500 to 1900	°C	Short dwell times (1 to 8 min)
Maximum Magnetic Modulation Contrast	~20	%	1740°C/8 min sample, 532 nm excitation
Standard Magnetic Modulation Contrast	~5	%	850°C/2h control sample, 532 nm excitation
Highest NV^- Content (EPR)	9.8	ppm	Achieved at 1500°C/5 min RTA
V^- Defect Content (RTA 1900°C)	0	ppm	V^- defects practically quenched

Key Methodologies

The experimental procedure focused on optimizing the post-irradiation thermal treatment to control defect formation and lattice quality.

Material Preparation: Type Ib HPHT diamond particles (20 µm and 140 nm) containing ~110 ppm substitutional nitrogen were selected.
Vacancy Introduction: Particles were irradiated with high-energy electrons (3 MeV) to a fluence of 1.5 x 10¹⁹ e/cm² to create lattice vacancies.
Rapid Thermal Annealing (RTA): Irradiated particles were rapidly annealed in a high-temperature furnace across a range of conditions:
- 1500°C / 5 min
- 1700°C / 3 min
- 1900°C / 1 min
- 1740°C / 8 min (High-performing sample)
Purification and Surface Treatment: Following RTA, particles were oxidized in air (up to 850°C) to remove graphitic carbon, followed by acid reflux (concentrated H₂SO₄:HNO₃ 3:1) to achieve a carboxylated (-COOH) surface chemistry.
Characterization: Samples were analyzed using Continuous Wave X-band (9.4 GHz) Electron Paramagnetic Resonance (EPR) at 50 K and Room Temperature (RT) to quantify paramagnetic defects (P1, V^-, Ni, NV^-).
Quantum Performance Measurement: Magnetic modulation of fluorescence was measured under static magnetic fields (~150 mT) using 514 nm, 532 nm, and 420 nm excitation wavelengths to determine contrast percentage.

6CCVD Solutions & Capabilities

The findings of Torelli et al. underscore the critical role of high-purity diamond material and precise thermal processing in achieving superior quantum properties. 6CCVD is uniquely positioned to supply and engineer the necessary materials to replicate and advance this research, particularly for scaling up quantum sensor production.

Applicable Materials for Quantum Sensing

To achieve the high-quality NV^- centers and lattice healing demonstrated by RTA, researchers require diamond with exceptional purity and controlled nitrogen content.

6CCVD Material Recommendation	Description & Relevance to Research
Electronic Grade SCD	Ideal for maximizing spin coherence times (T₂) and T₁ relaxation. Our SCD material offers extremely low intrinsic nitrogen and defect content, allowing researchers to precisely control NV^- formation via targeted ion implantation and RTA, minimizing parasitic defects.
Optical Grade PCD	Suitable for large-area sensing arrays or high-volume particle production. Our PCD wafers (up to 125mm) can be processed, irradiated, and then milled into high-quality micro- or nanodiamonds, offering superior uniformity compared to HPHT precursors.
Custom Nitrogen Doping	While the paper used ~110 ppm N, 6CCVD can tailor nitrogen incorporation during MPCVD growth to optimize the NV^- yield for specific RTA recipes, ensuring maximum performance without quenching.

Customization Potential for Advanced Quantum Devices

The successful implementation of RTA-enhanced diamond requires precise control over geometry and integration into device architectures.

Custom Dimensions: 6CCVD provides SCD and PCD plates/wafers up to 125mm in diameter, with thicknesses ranging from 0.1 µm to 500 µm. This enables the fabrication of large-scale sensing platforms or substrates for subsequent particle generation.
Precision Processing: We offer advanced laser cutting and milling services to produce custom-sized micro- or nanodiamond particles from high-purity CVD material, ensuring geometric uniformity critical for reproducible quantum performance.
Integrated Metalization: For integrating NV sensors into functional devices (e.g., for microwave delivery in ODMR or magnetic field generation), 6CCVD offers in-house metalization capabilities, including Ti, Pt, Au, Pd, W, and Cu thin films.

Engineering Support

The RTA process is highly sensitive to material quality and temperature profiles. 6CCVD’s in-house team of PhD material scientists specializes in defect engineering and thermal processing of CVD diamond.

RTA Recipe Optimization: We provide consultation on optimizing RTA parameters (temperature, dwell time, atmosphere) to maximize NV^- yield and magnetic modulation contrast based on the specific starting material and desired application (e.g., maximizing T₁ for relaxometry or maximizing contrast for imaging).
Material Selection Guidance: Our experts assist in selecting the optimal diamond type (SCD vs. PCD) and purity level to ensure successful replication and extension of high-temperature annealing research for quantum sensing projects.

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

View Original Abstract

Fluorescence of the negatively charged nitrogen-vacancy (NV-) center of diamond is sensitive to external electromagnetic fields, lattice strain, and temperature due to the unique triplet configuration of its spin states. Their use in particulate diamond allows for the possibility of localized sensing and magnetic-contrast-based differential imaging in complex environments with high fluorescent background. However, current methods of NV- production in diamond particles are accompanied by the formation of a large number of parasitic defects and lattice distortions resulting in deterioration of the NV- performance. Therefore, there are significant efforts to improve the quantum properties of diamond particles to advance the field. Recently it was shown that rapid thermal annealing (RTA) at temperatures much exceeding the standard temperatures used for NV- production can efficiently eliminate parasitic paramagnetic impurities and, as a result, by an order of magnitude improve the degree of hyperpolarization of 13C via polarization transfer from optically polarized NV- centers in micron-sized particles. Here, we demonstrate that RTA also improves the maximum achievable magnetic modulation of NV- fluorescence in micron-sized diamond by about 4x over conventionally produced diamond particles endowed with NV-. This advancement can continue to bridge the pathway toward developing nano-sized diamond with improved qualities for quantum sensing and imaging.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphy.2020.00205

References

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2013 - The nitrogen-vacancy colour centre in diamond [Crossref]
2014 - Nitrogen-vacancy centers in diamond: nanoscale sensors for physics and biology [Crossref]
2019 - Targeting fluorescent nanodiamonds to vascular endothelial growth factor receptors in tumor [Crossref]
2019 - Brilliant blue, green, yellow, and red fluorescent diamond particles: synthesis, characterization, and multiplex imaging demonstrations [Crossref]
2014 - Multi-color imaging of fluorescent nanodiamonds in living hela cells using direct electron-beam excitation [Crossref]
2019 - Optical detection of intracellular quantities using nanoscale technologies [Crossref]
2018 - Nanodiamonds and their applications in cells [Crossref]
2018 - Diamond nanothermometry [Crossref]
2018 - Toward using fluorescent nanodiamonds to study chronological aging in Saccharomyces cerevisiae [Crossref]