Determining the Dependence of Single Nitrogen−Vacancy Center Light Extraction in Diamond Nanostructures on Emitter Positions with Finite−Difference Time−Domain Simulations

At a Glance

Metadata	Details
Publication Date	2023-12-31
Journal	Nanomaterials
Authors	Tianfei Zhu, Jia Zeng, Feng Wen, Hongxing Wang
Institutions	Xi’an Jiaotong University
Analysis	Full AI Review Included

Technical Analysis and Documentation: Optimized NV Center Light Extraction in Diamond Nanostructures

6CCVD Material Science Division Application Focus: Quantum Sensing, Single-Photon Sources, Nano-Optics

Executive Summary

This research validates critical design parameters for maximizing photon extraction efficiency (PEE) from single Nitrogen-Vacancy (NV) centers embedded in diamond nanostructures. The findings provide essential guidance for engineers developing high-performance quantum devices.

Peak Performance Achieved: Simulated PEE reached 57.96% in a nanocone geometry, significantly exceeding the performance of bulk diamond emitters (critical angle 24.4°).
Geometry Dependence: Nanocone structures demonstrated superior performance for s-polarized emitters, while nanopillars were better suited for p-polarized emitters (38.40% PEE).
Critical Design Factors: PEE is highly sensitive to nanostructure geometry, emitter depth (optimal depth identified at 25 nm from the top), and dipole polarization angle.
Material Requirement: Successful fabrication requires high-quality, low-defect density IIa-type (001) Single Crystal Diamond (SCD) grown via Chemical Vapor Deposition (CVD).
Methodology: Finite-Difference Time-Domain (FDTD) simulations were used to model the optical coupling differences, supported by experimental fabrication using thermal annealing and Inductively Coupled Plasma (ICP) etching.
Commercial Impact: These results directly inform the design and fabrication of next-generation NV center-based micro- and nano-optics for quantum information processing and high-precision sensing.

Technical Specifications

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

Parameter	Value	Unit	Context
Peak PEE (Nanocone)	57.96	%	s-polarized dipole, 25 nm depth
Peak PEE (Nanopillar)	38.40	%	p-polarized dipole
Emitter Wavelength	637	nm	NV Center zero-phonon line (ZPL)
Diamond Refractive Index (n)	2.42	N/A	Used in FDTD simulation
Objective Numerical Aperture (NA)	0.95	N/A	Photon collection setting
Nanocone Actual Height	415	nm	Measured via SEM
Nanocone Base Diameter	290	nm	Measured via SEM
Nanocone Cone Angle	33.01	°	Calculated from SEM
CVD Growth Pressure	100	Torr	Total gas pressure during growth
CVD H₂ Flow Rate	500	sccm	Hydrogen carrier gas
CVD O₂ Flow Rate	2.9	sccm	Used to suppress defect formation
CVD CH₄ Flow Rate	40	sccm	Carbon source gas

Key Methodologies

The nanostructures were fabricated on high-quality SCD using a combination of CVD growth, lithography, thermal annealing, and dry etching.

Material Growth: IIa-type Single Crystal Diamond (SCD) was grown via CVD on a High-Pressure/High-Temperature (HPHT) diamond substrate (3 mm x 3 mm x 0.5 mm). The growth process included the addition of O₂ gas (2.9 sccm) to maintain high material quality and restrain defect formation.
Mask Preparation: A standard photolithography process was used to define 1 µm diameter round hole patterns in a 3 µm thick SPR-220 photoresist layer.
Gold Deposition and Lift-Off: A 10 nm thick gold film was deposited via electron beam evaporation, followed by a lift-off process to create gold disks.
Thermal Annealing: Samples were annealed at 1100 °C for 5 minutes. This process utilized the metal dewetting effect, transforming the micro-sized gold disks into nanoscale gold spheres, which served as the hard etch mask.
Nanostructure Etching (ICP): The diamond was etched using Inductively Coupled Plasma (ICP) etching to form the nanocones.
- Etching Gas: O₂ (50 sccm flow rate).
- Chamber Parameters: 10 mTorr pressure, 450 W coil power.
- Bias Control: 25 W platen power (critical for achieving the nanocone morphology).
Simulation: FDTD software (Lumerical Solutions 2017a) was used to model the emission properties of electric dipoles (NV centers) at various depths (25 nm to 100 nm) and polarization angles (0° to 90°).

6CCVD Solutions & Capabilities

This research highlights the critical need for ultra-high-purity, low-defect Single Crystal Diamond (SCD) and precise nanostructure fabrication control—core competencies of 6CCVD. Our capabilities are perfectly aligned to replicate, optimize, and scale the production of these high-performance quantum materials.

Applicable Materials

To replicate or extend this research, the material must possess extremely low nitrogen content and high crystalline quality to ensure long coherence times (T₂) and stable NV center formation.

6CCVD Material Recommendation	Specification Alignment	Customization Potential
Optical Grade SCD (001)	Ultra-low nitrogen concentration (IIa type) is essential for high-coherence NV centers and minimal background fluorescence.	We offer SCD plates in standard (001) orientation, crucial for aligning the NV center axis, up to 500 µm thick.
Custom Substrates	The paper used 3 mm x 3 mm substrates.	6CCVD provides custom dimensions and thicknesses, including substrates up to 10 mm thick, allowing for robust handling during complex processing steps like ICP etching and annealing.
Polycrystalline Diamond (PCD)	While the paper focused on SCD, PCD may be suitable for large-area, cost-sensitive applications where random crystal orientation is acceptable.	We offer PCD wafers up to 125 mm diameter with high uniformity, suitable for scaling up nanostructure arrays.

Customization Potential for Advanced Nano-Optics

The success of this research hinges on precise control over nanostructure geometry and surface quality. 6CCVD offers specialized services to meet these demands:

Precision Polishing: Achieving uniform nanostructure arrays requires an atomically smooth starting surface. We guarantee SCD polishing to Ra < 1 nm and inch-size PCD polishing to Ra < 5 nm, ensuring optimal conditions for subsequent lithography and etching processes (e.g., photoresist spinning and gold deposition).
Custom Metalization Services: Although the paper used gold only as an etch mask, future integrated quantum devices will require electrical contacts. 6CCVD offers internal metalization capabilities, including:
- Metals: Au, Pt, Pd, Ti, W, and Cu.
- Application: Custom layer stacks (e.g., Ti/Pt/Au) can be deposited and patterned for integrated microwave control lines or electrical readout structures adjacent to the nanostructures.
Advanced Processing Support: We offer laser cutting and shaping services to produce custom-sized substrates or probe tips, facilitating integration into complex experimental setups (e.g., AFM probes or micro-optical systems).

Engineering Support & Call to Action

The complex dependence of PEE on geometry, depth, and polarization demonstrated in this paper requires expert material selection and process optimization.

Expert Consultation: 6CCVD’s in-house PhD team specializes in quantum materials and can assist engineers and scientists with material selection, defect engineering (e.g., optimizing nitrogen incorporation for NV creation), and surface preparation for similar NV Center Quantum Sensing and Single-Photon Source projects.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) for time-sensitive research and development projects.

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

View Original Abstract

In this study, we obtained a diamond nanocone structure using the thermal annealing method, which was proposed in our previous work. Using finite-difference time-domain (FDTD) simulations, we demonstrate that the extraction efficiencies of nitrogen-vacancy (NV) center emitters in nanostructures are dependent on the geometries of the nanocone/nanopillar, emitter polarizations and axis depths. Our results show that nanocones and nanopillars have advantages in extraction from emitter dipoles with s− and p−polarizations, respectively. In our simulations, the best results of collection efficiency were achieved from the emitter in a nanocone with s−polarization (57.96%) and the emitter in a nanopillar with p−polarization (38.40%). Compared with the nanopillar, the photon extraction efficiency of the emitters in the nanocone is more sensitive to the depth and polarization angle. The coupling differences between emitters and the nanocone/nanopillar are explained by the evolution of photon propagation modes and the internal reflection effects in diamond nanostructures. Our results could have positive impacts on the design and fabrication of NV center−based micro− and nano−optics in the future.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano14010099

References

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