Hyperfine Coupling Constants of Photoinduced Axial Symmetry NV Centers in a 6H Silicon Carbide - DFT and High-Field ENDOR Spectroscopy Study

At a Glance

Metadata	Details
Publication Date	2025-10-31
Journal	Applied Nano
Authors	Yuliya Ermakova, Ekaterina Dmitrieva, I. N. Gracheva, D. V. Shurtakova, Margarita A. Sadovnikova
Institutions	Ioffe Institute, Plekhanov Russian University of Economics
Analysis	Full AI Review Included

Technical Documentation & Analysis: NV Centers in 6H Silicon Carbide

This document analyzes the research on Nitrogen-Vacancy (NV) centers in 6H Silicon Carbide (SiC) using high-field Electron Nuclear Double Resonance (ENDOR) spectroscopy. While the study focuses on SiC, the findings directly validate the critical role of stable, high-coherence spin defects—a core application area for 6CCVD’s Single Crystal Diamond (SCD) materials.

Executive Summary

Core Achievement: Experimental determination of hyperfine (HFI) and nuclear quadrupole interaction (NQI) constants for photoinduced axial NV centers (hh position) in 6H-SiC using high-frequency (94 GHz) EPR and ENDOR spectroscopy.
Microscopic Model Validation: Density Functional Theory (DFT) calculations confirmed the NV center’s microscopic structure as a nearest N-V_Si pair, with spin density predominantly localized on the planar Si-C plane.
Quantum Stability Demonstrated: The spin Hamiltonian parameters (Zero-Field Splitting D, NQI Q, HFI A) exhibit remarkable temperature stability, particularly below 100 K, which is critical for reliable quantum control.
Temperature Sensitivity: The hyperfine interaction parameter (A) showed a weak temperature dependence quantified at $\delta$A/$\delta$T $\approx$ 180 Hz/K, necessitating temperature compensation in high-precision quantum devices.
Practical Quantum Platform: The established temperature stability of spin Hamiltonian values validates 6H-SiC NV centers as promising, scalable solid-state qubits capable of room-temperature operation for RF sensing and quantum information processing, mirroring key advantages of diamond NV centers.
6CCVD Relevance: This research underscores the demand for high-purity, engineered wide-bandgap materials, directly aligning with 6CCVD’s expertise in producing SCD and PCD substrates optimized for NV defect creation and quantum applications.

Technical Specifications

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

Parameter	Value	Unit	Context
Host Material Polytype	6H-SiC (²⁸Si enriched)	N/A	Substrate for NV center formation
EPR Operating Frequency	94	GHz	W-band high-field spectroscopy
Primary Magnetic Field (B₀)	3397.5 (≈ 3.4)	mT (T)	High-field ENDOR measurement
Hyperfine Interaction (A_\|\|)	-1.175	MHz	Experimental value (hh position, T=150 K)
Quadrupole Coupling (C_q)	2.523	MHz	Experimental value (hh position, T=150 K)
Isotropic Fermi Interaction (a_iso)	-1.175	MHz	Experimental value (hh position, T=150 K)
HFI Temperature Sensitivity	$\approx$ 180	Hz/K	$\delta$A/$\delta$T (measured between 100 K and 280 K)
Electron Irradiation Energy	2	MeV	Used to form vacancy defects
Electron Irradiation Fluence	4 x 10¹⁸	cm^-2	Defect creation dosage
Annealing Temperature	900	°C	Stabilization of negatively charged NV complexes
Sample Dimensions	450 x 450 x 670	µm³	Sample size for W-band EPR

Key Methodologies

The experiment combined advanced material synthesis, defect engineering, and high-resolution magnetic resonance techniques:

Material Synthesis: 6H-SiC crystals enriched with ²⁸Si (I=0) were grown via high-temperature sublimation (Physical Vapor Transport).
Doping: Nitrogen concentration was controlled to approximately C $\approx$ 10¹⁷ cm^-3.
Defect Creation: Samples were irradiated using high-energy (2 MeV) electrons at a fluence of 4 x 10¹⁸ cm^-2 to introduce vacancy defects.
Defect Stabilization: Irradiated crystals were annealed at T = 900 °C in an Argon atmosphere for 2 hours to form stable, negatively charged NV complexes.
Spectroscopy: High-frequency (94 GHz) EPR and ENDOR measurements were performed using a Bruker Elexsys E680 spectrometer.
- EPR utilized the Hahn pulse sequence ($\pi$MW/2-$\tau$-$\pi$MW-$\tau$-ESE).
- ENDOR utilized the Mims pulse sequence ($\pi$MW/2-$\tau$-$\pi$MW/2-$\tau$RF-$\pi$MW/2-$\tau$-ESE) with an RF source (1-250 MHz, 150 kW output).
Optical Pumping: Continuous wave IR laser ($\lambda$ = 980 nm, up to 500 mW) was used for photoinduced spin polarization, enabling Optically Detected Magnetic Resonance (ODMR) principles.
Computational Modeling: Density Functional Theory (DFT) calculations were executed using the Quantum ESPRESSO package (PBE functional) on a 36-unit cell supercell to derive theoretical HFI and NQI constants and map spin density distribution.

6CCVD Solutions & Capabilities

The research highlights the critical need for highly controlled, wide-bandgap materials for quantum technology. While the paper uses SiC, 6CCVD specializes in the industry-leading platform for NV centers: MPCVD Diamond. We offer materials and services essential to replicate, extend, and optimize this type of quantum research.

Applicable Materials for Quantum Spin Defects

To achieve the highest coherence times and stability required for advanced quantum registers, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): The ideal host matrix for NV centers. Our high-purity SCD substrates (low native nitrogen) are optimized for subsequent controlled defect creation (e.g., ion implantation followed by annealing) to produce high-coherence NV^- ensembles.
Engineered Nitrogen Doping: We offer SCD wafers with precise, controlled nitrogen concentrations (ppm to ppb level) grown in situ via CVD, allowing researchers to bypass the high-fluence irradiation steps used in the SiC study and achieve superior defect uniformity.
Boron-Doped Diamond (BDD): For applications extending into electrochemical sensing or high-temperature electronics, our BDD materials provide robust, conductive platforms compatible with quantum sensing protocols.

Customization Potential & Fabrication Services

The SiC study utilized a small, custom-cut sample (450 x 450 x 670 µm³) for W-band EPR. 6CCVD excels at providing materials tailored to specific experimental setups:

Research Requirement	6CCVD Capability	Specification Range
Custom Dimensions	Precision laser cutting and shaping of plates/wafers.	SCD (0.1 µm - 500 µm thickness); PCD (up to 125mm diameter).
Surface Quality	Ultra-smooth polishing essential for minimizing surface noise in high-resolution spectroscopy.	SCD: Ra < 1 nm; Inch-size PCD: Ra < 5 nm.
High-Frequency Integration	In-house metalization for creating microwave striplines or contact pads directly on the diamond surface.	Au, Pt, Pd, Ti, W, Cu metalization stacks available.
Substrate Thickness	Providing robust substrates for high-energy irradiation and annealing processes.	Substrates available up to 10 mm thickness.

Engineering Support & Global Logistics

Defect Engineering Consultation: 6CCVD’s in-house PhD team provides expert consultation on material selection, doping strategies, and post-processing optimization (e.g., annealing recipes) for similar Solid-State Qubit and Quantum Sensing projects. We help clients transition from SiC research to high-performance diamond platforms.
Global Supply Chain: We ensure reliable, timely delivery of custom diamond materials worldwide, offering DDU (default) and DDP shipping options to meet international research deadlines.

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

View Original Abstract

Solid-state spin centers are at the forefront of developing advanced quantum technologies, engaging in applications of sensing, communication and computing. A semiconductor host matrix compatible with existing silicon technology provides a robust platform for holding spin defects and an opportunity for external manipulation. In this article, negatively charged nitrogen-vacancy (NV) centers in the hexagonal hh position in a 6H polytype silicon carbide crystal was studied using high-frequency (94 GHz) electron paramagnetic (EPR) and electron nuclear double resonances (ENDOR) spectroscopy. Experimentally determined values of hyperfine and quadrupole interactions of 14N were compared with the values obtained for the centers in NVk2k1 positions. The distribution of spin density of the defect within a supercell of the SiC crystal lattice was calculated using the density functional theory approach. The theoretical estimation of electron-nuclear interaction constants turned out to be in close agreement with the experimental values, which allows us to refine the microscopic model of a point defect. The temperature dependence of the spin Hamiltonian values (δA/δT ≅ 180 Hz/K) was studied with the possibility of observing the 14N NMR signal at room temperature. The fundamental knowledge gained about interactions’ parameters’ behavior lays the foundation for the creation of promising quantum platforms.

Tech Support

Original Source

DOI: https://doi.org/10.3390/applnano6040023

References

2016 - Control of Spin Defects in Wide-Bandgap Semiconductors for Quantum Technologies
2018 - Material platforms for spin-based photonic quantum technologies [Crossref]
2021 - Quantum computer based on color centers in diamond [Crossref]
2015 - Optimal control of fast and high-fidelity quantum gates with electron and nuclear spins of a nitrogen-vacancy center in diamond [Crossref]
2020 - Silicon carbide color centers for quantum applications [Crossref]
2021 - Optical spin initialization of spin-3/2 silicon vacancy centers in 6H-SiC at room temperature [Crossref]
2017 - Characterization and formation of NV centers in 3 C, 4 H, and 6 H SiC: An ab initio study [Crossref]
2022 - Silicon carbide photonics bridging quantum technology [Crossref]