Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-09-16 |
| Journal | Nanophotonics |
| Authors | Jan Fait, M. Varga, Karel HruĆĄka, Alexander Kromka, Bohuslav Rezek |
| Institutions | Czech Academy of Sciences, Institute of Physics, Czech Technical University in Prague |
| Citations | 5 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Spectral Tuning of Diamond Photonic Crystal Slabs
Section titled âTechnical Documentation & Analysis: Spectral Tuning of Diamond Photonic Crystal SlabsâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel, two-step post-fabrication method for spectrally tuning diamond Photonic Crystal (PhC) slabs, overcoming the inherent challenges of achieving nanoscale precision in diamond nanostructuring.
- Core Innovation: A thin, Silicon Vacancy (SiV)-rich nanocrystalline diamond (NCD) layer is deposited onto a pre-patterned PhC slab, acting as a tuning layer to red-shift the leaky modes.
- Performance Metric: The method successfully shifted the photonic modes by over 100 nm to overlap precisely with the SiV center Zero-Phonon Line (ZPL) at 738 nm.
- Key Result: Achieved a ninefold (9x) enhancement of the SiV center emission intensity without requiring resonant excitation.
- Material Advantage: The use of NCD allows for high-density incorporation of SiV centers near the surface, which is crucial for sensing applications.
- Fabrication Solution: This deposition-based tuning approach avoids the need for extreme nanoscale precision in the initial lithography and etching steps, making the fabrication of high-performance diamond PhC structures more cost-effective and scalable.
- 6CCVD Relevance: This technique is directly applicable to 6CCVDâs high-quality Polycrystalline Diamond (PCD) and Single Crystal Diamond (SCD) materials, enabling the production of scalable, high-efficiency quantum and sensing devices.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research detailing the PhC structure and performance metrics.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Emission Wavelength (SiV ZPL) | 738 | nm | Zero-Phonon Line |
| PL Enhancement Factor | 9 | x | Highest observed enhancement (NA 0.4 and 0.5) |
| Spectral Shift Achieved | > 100 | nm | Shift required to align leaky modes to SiV ZPL |
| Tuning Layer Thickness (ttuning) | ~60 | nm | Deposited SiV-rich NCD layer |
| Original PhC Lattice Constant (L) | 390 | nm | Periodicity of columns |
| Original Column Diameter (d) | 215 | nm | Diameter of etched columns |
| Original PhC Thickness (tphc) | 105 | nm | Thickness of patterned layer |
| Original NCD Growth Rate | ~8 | nm/h | Used for the initial PhC slab |
| Tuning Layer Growth Rate | ~4 | nm/min | Used for the SiV-rich layer |
| TE0 Mode Coupling Efficiency Ratio (vs. TM0) | 1.22 | x | Higher coupling efficiency into TE0 mode |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a two-step MPCVD growth and nanofabrication process to achieve spectral tuning:
-
Initial NCD Growth (SiV-Free Layer):
- Substrate: Quartz, seeded with nanodiamond colloidal dispersion (4.8 ± 0.6 nm median size).
- Reactor: Linear antenna Microwave (MW) Plasma System (Roth & Rau AK 400).
- Parameters: Time (19 h), Pressure (10 Pa), H2 flow (200 sccm), CH4 flow (5 sccm), CO2 flow (20 sccm).
- Temperature/Power: Sample surface temperature (~540 °C), MW power (2 x 1.7 kW).
- Result: ~160 nm thick NCD layer without SiV center PL.
-
PhC Slab Fabrication (EBL & RIE):
- Patterning: Electron Beam Lithography (EBL) used to pattern poly(methyl methacrylate) resist (~100 nm thick).
- Masking: Gold (Au) layer (~70 nm thick) evaporated and lifted off.
- Etching: Reactive Ion Etching (RIE) using O2/CF4 plasma to create the PhC structure (columns).
-
Tuning Layer Deposition (SiV-Rich Layer):
- Reactor: Focused MW Plasma Reactor (Aixtron P6) using an ellipsoidal cavity resonator.
- Si Source: Common intrinsic Si wafer pieces placed near the sample, partially etched by plasma to serve as the Si source for SiV formation.
- Parameters: Time (15 min), Pressure (6 kPa), H2 flow (300 sccm), CH4 flow (3 sccm).
- Temperature/Power: Sample temperature (~820 °C), MW power (3 kW).
- Result: ~60 nm thick SiV-rich NCD layer deposited, red-shifting the leaky modes to 738 nm.
-
Surface Treatment:
- Process: Oxygen plasma treatment performed as a final step to terminate the surface, increasing the PL intensity of the near-surface SiV centers.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe demonstrated spectral tuning technique is highly relevant to advanced quantum and sensing applications. 6CCVD is uniquely positioned to supply the high-quality diamond materials and precision fabrication services required to replicate and scale this research.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Solution | Technical Advantage |
|---|---|---|
| Nanocrystalline Diamond (NCD) | Polycrystalline Diamond (PCD) | 6CCVD offers high-purity PCD wafers up to 125 mm in diameter, providing superior scalability and uniformity compared to the small 1 mmÂČ area used in the study. |
| SiV Center Incorporation | SiV-Doped PCD/SCD | Our MPCVD reactors are optimized for controlled incorporation of color centers (SiV, NV, GeV) during growth, ensuring high-density, near-surface emitter layers essential for sensing. |
| High-Efficiency Extraction | Optical Grade SCD | For ultimate performance and reduced scattering losses (a known issue in NCD/PCD), 6CCVD supplies Single Crystal Diamond (SCD) with Ra < 1 nm polishing, ideal for high-Q PhC cavities and nanobeams. |
| Refractive Index Tuning | Boron-Doped Diamond (BDD) | We offer BDD films, allowing researchers to explore electro-optic tuning mechanisms or integrate conductive layers directly into the PhC structure for active device control. |
Customization Potential for PhC Structures
Section titled âCustomization Potential for PhC StructuresâThe paper highlights the difficulty in achieving exact nanoscale dimensions via etching alone. 6CCVDâs capabilities directly address these precision challenges:
- Precision Layer Thickness: The tuning layer thickness (~60 nm) is critical. 6CCVD specializes in growing ultra-thin SCD and PCD films, offering thickness control from 0.1 ”m up to 500 ”m, enabling highly precise spectral tuning steps.
- Scalability: While the research used a 1 mmÂČ area, 6CCVD can provide large-area PCD plates up to 125 mm for high-throughput fabrication of PhC slabs using large-scale methods like nanoimprint lithography (as suggested in the paperâs conclusion).
- Surface Preparation: The quality of the PhC slab surface is paramount. 6CCVD provides ultra-smooth polishing (Ra < 5 nm for inch-size PCD and Ra < 1 nm for SCD), minimizing the non-directional scattering losses observed in the NCD material used in this study.
- Integrated Metalization: For advanced device integration (e.g., electrical contacts for thermal or electro-optic tuning), 6CCVD offers in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu deposition.
Engineering Support
Section titled âEngineering SupportâThe successful replication and extension of this researchâparticularly the precise control of SiV concentration and the growth rate for nanoscale tuningârequires deep expertise in MPCVD diamond synthesis.
- 6CCVDâs in-house PhD-level engineering team specializes in material selection and recipe optimization for quantum optics and biosensing projects. We can assist researchers in designing the optimal diamond stack (e.g., SCD vs. PCD, SiV concentration profile, and tuning layer thickness) for similar Photonic Crystal Sensing applications.
- We provide global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond solutions worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.