Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-07-14 |
| Journal | Scientific Reports |
| Authors | Ranjith Rajasekharan Unnithan, GĂŒnter Kewes, Amir Djalalian-Assl, Kumaravelu Ganesan, Snjezana TomljenovicâHanic |
| Institutions | Humboldt-UniversitÀt zu Berlin, The University of Melbourne |
| Citations | 13 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: High-Efficiency Photon Extraction from NV Centers in Nanodiamond
Section titled â6CCVD Technical Documentation: High-Efficiency Photon Extraction from NV Centers in NanodiamondâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the design and performance of a micro-concave waveguide antenna developed to achieve highly efficient, directional photon extraction from negatively charged Nitrogen Vacancy (NV-) centers in nanodiamond (ND).
The design successfully mitigates the key challenges associated with NV center emission: two orthogonal dipoles and a high refractive index medium (diamond, n=2.4).
- High Collection Efficiency: The waveguide antenna achieves collection efficiency exceeding 80% (81% to 85% demonstrated for perpendicular and parallel dipoles, respectively) within a narrow 90° full cone angle.
- Spontaneous Emission Rate (SPE) Enhancement: The device significantly enhances the spontaneous emission rate, providing a maximum calculated enhancement factor of up to 30x (with a highly efficient operating point of 18x cited).
- Orientation Insensitivity: Collection efficiency is robust and largely independent of the NV dipole orientation (parallel, perpendicular, or 45°), a critical achievement for integrated quantum devices using randomly oriented nanodiamonds.
- Positional Robustness: The geometry is robust against offsets in dipole positioning (within 80 nm offset in the x-axis, SPE reduction is <20%), accommodating typical nanodiamond size and fabrication tolerances.
- Target Wavelength: Optimized for the spectral peak of NV- luminescence in nanodiamonds at room temperature, corresponding to 700 nm vacuum wavelength.
- Core Structure: Utilizes a semiconductor substrate (Si), thick reflective metal layer (Ag), and a high-index dielectric waveguide layer (SiNx, n=2.0) shaped into a micro-concave mirror.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Emitter Type | NV- Center in Nanodiamond | - | Single photon source. |
| ND Refractive Index (n) | 2.4 | - | High-index medium challenge. |
| ND Sphere Radius | 40 | nm | Used for simulation model. |
| Emission Wavelength (λvac) | 700 | nm | Spectral peak of NV- luminescence. |
| SiNx Refractive Index (n) | 2.0 | - | Dielectric waveguide layer. |
| Optimized Cavity Radius (RAg) | 900 | nm | Radius of curvature of silver film. |
| Substrate Radius (Rs) | 1200 | nm | Required for geometry calculation (RAg = Rs - TAg). |
| Silver Thickness (TAg) | 300 | nm | Used as reflective mirror. |
| SiNx Layer 1 Thickness (TSiNx) | 365 / 315 | nm | Optimized thickness for |
| Collection Efficiency (NA=0.8) | 87.0% | - | For parallel dipole orientation. |
| Collection Efficiency (NA=0.8) | 83.8% | - | For perpendicular dipole orientation. |
| Max SPE Enhancement | ~30 | x | Maximum spontaneous emission rate enhancement achieved. |
| Efficient SPE Enhancement | 18 | x | Accompanying efficiency increase factor. |
| Output Cone Angle (Full) | 90 | ° | Achieved collection angle (50° to 140° range). |
| NA of Collected Light | 0.707 | - | Corresponding to the 90° full cone angle. |
| Axial Position Tolerance (FWHM) | 195 ( | ) / 144 (⊥) |
Key Methodologies
Section titled âKey MethodologiesâThe theoretical study utilized a rigorous 3D computational approach, followed by physical fabrication to confirm feasibility:
- Modeling Platform: The micro-cavity antenna was computationally investigated in 3D using the Finite Element Method (FEM) implemented in COMSOL MULTIPHYSICS 4.3b.
- Geometry Definition: A semi-spherical concave cavity structure was defined on a Silicon (Si) substrate, forming the base of the antenna.
- Reflective Layer Deposition: A thick 300 nm Silver (Ag) film was coated onto the concave Si surface to act as the reflecting mirror (Radius RAg=900 nm).
- Dielectric Waveguide Layer: A first layer of Silicon Nitride (SiNx, n=2.0) was deposited to form the base waveguide and set the critical height (De) for the NV emitter (TSiNx varied between 315 nm and 365 nm based on dipole orientation).
- Emitter Placement: A 40 nm radius nanodiamond sphere containing the NV center dipole was placed at the center of the cavity at the optimal height De (near the focal point f=RAg/2n).
- Full Waveguide Formation: A second layer of SiNx (TâSiNx=300 nm) was deposited on top of the emitter to fully encapsulate the nanodiamond and complete the waveguide structure.
- Fabrication Demonstration: A cavity antenna of similar dimensions was fabricated on a silicon substrate using Focused Ion Beam (FIB) to demonstrate technical feasibility.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced diamond materials and engineering services required to replicate, refine, and integrate these high-performance quantum antennas into operational devices.
Applicable Materials
Section titled âApplicable MaterialsâThe successful operation of this antenna relies on integrating a high-quality emitter (NV center) within a stable, high-index host (diamond). 6CCVD provides the optimal platform material for this research area:
- Optical Grade Single Crystal Diamond (SCD): Required for applications demanding extremely low strain and high crystal purity essential for stable, high-coherence NV center formation (either via implantation or in-situ growth).
- Recommendation: High-purity, electronic or optical grade SCD wafers, ideal for establishing stable NV centers and supporting complex lithographic structures on ultra-flat surfaces.
- Polycrystalline Diamond (PCD) Substrates: For larger scale, cost-sensitive integration projects where nanodiamonds or implanted NV layers are integrated onto a durable platform.
- Capability Match: We offer PCD plates/wafers up to 125 mm diameter, enabling scalable manufacturing trials for quantum devices.
- Custom Thicknesses: We provide SCD and PCD materials with thicknesses ranging from 0.1 ”m up to 500 ”m, allowing engineers to fine-tune material properties (like substrate thermal management or proximity to surface) precisely to the antennaâs design requirements.
Customization Potential
Section titled âCustomization PotentialâThe device detailed in the research utilizes complex layering and specific geometric parameters (concave mirrors, optimized dielectric thickness). 6CCVD provides essential capabilities needed for replicating and advancing this structure:
| Requirement from Paper | 6CCVD Capability | Engineering Value Proposition |
|---|---|---|
| Precise Layering (Ag mirror) | Custom Metalization Services | We offer in-house deposition of metals including Au, Pt, Pd, Ti, W, and Cu. We can consult on the subsequent deposition of Ag or provide the metal stack required for adhesion and electrical contact prior to SiNx deposition. |
| Complex Geometry (Concave Cavity) | Advanced Diamond Shaping & Cutting | While the cavity was fabricated on Si, for diamond-integrated antennas, 6CCVD offers precision laser micro-machining and custom shaping services to meet unique R&D geometry requirements (e.g., custom mesa structures or localized material removal). |
| Ultra-Flat Interfaces | Superior Polishing Quality | Our SCD materials are polished to an industry-leading surface roughness of Ra < 1 nm, providing the ultra-flat interface necessary for reliable, low-loss deposition of the Ag mirror and SiNx waveguide layers. |
| High Refractive Index Compatibility | Diamond Etching and Surface Termination | We ensure diamond surfaces are optimally prepared and terminated for subsequent processing steps, vital for seamless integration with high-index dielectrics like SiNx (n=2.0) or integration of nanodiamonds (n=2.4). |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD-level engineering team specializes in MPCVD diamond growth and advanced material integration for solid-state quantum systems. We can assist researchers and engineers with:
- Material Selection: Determining the optimal grade and thickness of SCD or PCD required for specific quantum computation and single-photon source projects, especially concerning NV center integration, strain minimization, and thermal management.
- Metal Stack Optimization: Consulting on metalization recipes (e.g., Ti/Pt/Au contact stacks) that ensure robust adhesion and low electrical resistance in the harsh environment often present in cavity QED experiments.
- Global Supply Chain Reliability: Providing reliable, globally shipped material (DDU default, DDP available) necessary for fast-paced international research cycles.
For custom specifications or material consultation on high-efficiency photon extraction projects, visit 6ccvd.com or contact our engineering team directly.