Localized nitrogen-vacancy centers generated by low-repetition rate fs-laser pulses

At a Glance

Metadata	Details
Publication Date	2022-10-07
Journal	Diamond and Related Materials
Authors	Charlie Oncebay, Juliana M. P. Almeida, Gustavo F. B. Almeida, Sérgio Ricardo Muniz, Cléber Renato Mendonça
Institutions	Universidade Federal de Uberlândia, Universidade de São Paulo
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Localized NV Center Generation

This documentation analyzes the research on generating localized Nitrogen-Vacancy (NV) centers using low-repetition rate femtosecond (fs) laser pulses in CVD diamond. The findings are leveraged to highlight 6CCVD’s superior material solutions for advanced quantum technology applications.

Executive Summary

This study successfully demonstrates a method for creating spatially localized NV centers in synthetic CVD diamond using low-repetition rate fs-laser irradiation, an important step for scalable quantum device fabrication.

Core Achievement: Generation of active, localized NV centers confirmed by Optically Detected Magnetic Resonance (ODMR) using 150 fs pulses at 775 nm and a 1 kHz repetition rate.
Material Used: Type-Ib CVD diamond (5x5x1 mm³) with nitrogen impurity level below 1 ppm.
Optimal Processing: Identified the optimal irradiation regime as 11-34 mJ/cm² fluence, with the best results (minimal damage) achieved at 14 mJ/cm² and the laser focus positioned 15-20 µm above the surface.
Post-Processing: Required annealing at 680 °C for 30 minutes and subsequent acid cleaning (HCl:HNO₃:H₂SO₄) to remove amorphous carbon and surface impurities.
Quantum Challenge: Zero-field ODMR spectra revealed a broad dual-dip (~25 MHz splitting), attributed to significant lattice strain induced by the fs-laser ablation process.
Implication for 6CCVD: The observed lattice strain necessitates the use of ultra-high purity, low-strain Single Crystal Diamond (SCD) to achieve the long coherence times required for practical quantum information applications.

Technical Specifications

The following table summarizes the critical experimental parameters and measured values extracted from the research paper.

Parameter	Value	Unit	Context
Initial Material Type	Type-Ib Synthetic CVD	N/A	Used for NV generation
Nitrogen Impurity Level	< 1	ppm	Material specification
Laser Pulse Duration	150	fs	Ti:sapphire laser source
Laser Wavelength	775	nm	Excitation source for defect generation
Laser Repetition Rate	1	kHz	Low-repetition rate regime
Damage Threshold Fluence (F_th)	1.3 ± 0.1	mJ/cm²	Determined by zero-damage method
Optimal Fluence Range	11 - 34	mJ/cm²	For active defect generation with minimal damage
Optimal Focus Position (Z)	15 - 20	µm	Above the sample surface
Annealing Temperature	680	°C	Post-irradiation thermal treatment
Annealing Duration	30	minutes	Post-irradiation thermal treatment
ODMR Resonance Frequency	~2870	MHz	Ground state NV^- center transition
ODMR Strain-Induced Splitting	~25	MHz	Zero-field dual-dip broadening

Key Methodologies

The generation and characterization of localized NV centers involved precise fs-laser microfabrication and advanced spectroscopic analysis.

Material Preparation: Use of 5x5x1 mm³ Type-Ib CVD diamond with nitrogen impurity below 1 ppm.
Fs-Laser Irradiation: Sample exposed to 150 fs, 775 nm laser pulses at a 1 kHz repetition rate. The sample was translated at a constant speed of 10 µm/s.
Parameter Mapping: Systematically varied pulse fluence (F) and laser focus position (Z) to determine the damage threshold (F_th) and the optimal conditions for defect creation with minimal surface damage.
Thermal Annealing: Post-irradiation annealing performed at 680 °C for 30 minutes to mobilize laser-generated vacancies, allowing them to bind with substitutional nitrogen impurities (V + N → NV).
Chemical Cleaning: Final cleaning stage using a 1:1:1 mixture of hydrochloric acid, nitric acid, and sulfuric acid to remove amorphous carbon and surface residues.
Characterization: NV center generation confirmed using Photoluminescence (PL) (543 nm and 532 nm excitation), Raman Spectroscopy (514 nm), and Optically Detected Magnetic Resonance (ODMR) at room temperature (300 K).

6CCVD Solutions & Capabilities

The research successfully demonstrated localized NV center generation but highlighted a critical limitation: significant lattice strain caused by the fs-laser process, which negatively impacts quantum coherence. 6CCVD provides ultra-high purity MPCVD diamond materials and precision engineering services specifically designed to mitigate these issues and advance quantum diamond research.

Applicable Materials for Quantum Applications

The Type-Ib material used (< 1 ppm N) is insufficient for high-coherence quantum applications. 6CCVD recommends the following material upgrade:

Electronic Grade Single Crystal Diamond (SCD):
- Purity: Nitrogen concentration < 5 ppb (parts per billion).
- Advantage: This ultra-low nitrogen content drastically reduces background paramagnetic impurities and minimizes residual lattice strain, which is essential for achieving long NV center coherence times (T₂) and mitigating the strain-induced ODMR broadening observed in the paper.
- Format: Available as plates/wafers up to 500 µm thick, or substrates up to 10 mm thick, suitable for bulk or thin-film quantum device integration.

Customization Potential & Engineering Services

To replicate or extend this fs-laser microfabrication technique for practical quantum devices, 6CCVD offers comprehensive customization capabilities:

Research Requirement / Challenge	6CCVD Solution & Capability	Technical Specification
Surface Quality for Fs-Laser (Minimizing surface damage and strain)	Ultra-Precision Polishing	SCD surfaces polished to Ra < 1 nm, ensuring minimal surface defects that could exacerbate strain during laser ablation.
Custom Device Integration (Need for specific chip sizes)	Custom Dimensions & Laser Cutting	Plates/wafers available up to 125 mm (PCD). Custom laser cutting services to achieve precise sample dimensions (e.g., 5x5 mm²) or complex geometries for integrated photonics.
Microwave Control Integration (ODMR requires MW delivery)	Custom Metalization Services	In-house deposition of thin films (Au, Pt, Pd, Ti, W, Cu) for fabricating on-chip microwave waveguides or electrical contacts necessary for efficient ODMR/ESR control.
Strain Mitigation Support (Optimizing post-processing)	In-House PhD Engineering Support	Our team provides consultation on optimizing post-growth and post-irradiation annealing recipes (like the 680 °C step used here) to minimize residual strain and maximize the yield of high-quality NV^- centers.
Scalability (Moving beyond small samples)	Large Area PCD Wafers	For scalable sensor arrays or integrated devices, we offer Polycrystalline Diamond (PCD) wafers up to 125 mm diameter, polished to Ra < 5 nm.

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.diamond.2022.109426

References

2009 - The ‘type’ classification system of diamonds and its importance in gemology (vol 45, pg 96, 2009)
1997 - Electron paramagnetic resonance imaging of the distribution of the single substitutional nitrogen impurity through polycrystalline diamond samples grown by chemical vapor deposition [Crossref]
2011 - Properties of nitrogen-vacancy centers in diamond: the group theoretic approach [Crossref]
2010 - Optical properties of the nitrogen-vacancy singlet levels in diamond [Crossref]
2006 - Single defect centres in diamond: a review [Crossref]
2006 - Processing quantum information in diamond [Crossref]
2006 - Room-temperature coherent coupling of single spins in diamond [Crossref]
2013 - Quantum logic readout and cooling of a single dark electron spin [Crossref]
2013 - Heralded entanglement between solid-state qubits separated by three metres [Crossref]