Fabrication of photonic amorphous diamonds for terahertz-wave applications
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-05-09 |
| Journal | Applied Physics Letters |
| Authors | Yuichiro Komiyama, Hiroyuki Abé, Yasushi Kamimura, Keiichi Edagawa |
| Institutions | The University of Tokyo |
| Citations | 7 |
| Analysis | Full AI Review Included |
Fabrication of Photonic Amorphous Diamond (PAD) Structures for Terahertz Applications
Section titled âFabrication of Photonic Amorphous Diamond (PAD) Structures for Terahertz ApplicationsâAnalysis of Appl. Phys. Lett. 108, 191110 (2016) by Komiyama et al. for 6CCVD Engineering Solutions.
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the fabrication and characterization of Photonic Amorphous Diamond (PAD) structures operating in the terahertz (THz) regime, validating a novel approach to 3D light confinement. 6CCVD identifies this work as highly relevant to next-generation THz device engineering, where our high-purity MPCVD diamond materials offer significant performance advantages over the ceramic materials used in the study.
- Core Achievement: Fabrication of a 3D Photonic Bandgap (PBG) structure using a diamond-like random network (PAD) in the THz frequency range (0.1-1.1 THz).
- Key Result: A complete 3D PBG was demonstrated at approximately 0.45 THz using terahertz time-domain spectroscopy.
- Material Challenge: The experiment utilized sintered alumina (Al2O3) rods (effective dielectric constant Δ â 7.5) containing internal pores (27% volume fraction), which introduced significant Rayleigh scattering losses.
- Wave Physics Confirmed: Diffusive THz-wave propagation was observed in the passbands, and the scattering mean free path reached the Ioffe-Regel threshold value for wave localization (2Ïl/λ â 1.5).
- Methodology: Structures were created via scanning laser lithography (additive manufacturing) using acrylic resin/alumina powder, followed by high-temperature dewaxing and sintering.
- 6CCVD Value Proposition: High-purity, low-loss MPCVD Single Crystal Diamond (SCD) or Polycrystalline Diamond (PCD) offers a superior, pore-free, high-dielectric alternative to sintered alumina, drastically reducing scattering losses and enhancing device efficiency for high-power THz applications.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper detailing the physical and optical characteristics of the fabricated PAD structures:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Photonic Bandgap (PBG) Frequency | ~0.45 | THz | Fundamental 3D PBG position. |
| Operating Frequency Range | 0.15 - 2.2 | THz | Terahertz time-domain spectroscopy range. |
| Effective Dielectric Constant (Δ) | ~7.5 | N/A | Estimated for the sintered alumina rods. |
| Pore Volume Fraction | 27 | % | Internal porosity within the sintered rods. |
| Rod Length (d) (Processed) | ~0.17 | mm | Characteristic dimension of the final PAD structure. |
| Sample Dimensions (Processed) | 3.1 x 3.3 x 1.1 | mm3 | Final size after dewaxing and sintering. |
| Minimum Transmittance (Tmin) | 1.0 x 10-3 - 1.0 x 10-2 | N/A | Observed near and above the bandgap. |
| Ioffe-Regel Localization Metric | ~1.5 | N/A | Value achieved at the band edge (Threshold â 1). |
| Rayleigh Scattering Reduction (TR) | exp(-A·f4) | N/A | Frequency-dependent loss mechanism observed. |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication of the Photonic Amorphous Diamond (PAD) structures involved a multi-step additive manufacturing and thermal processing sequence:
- CAD Design: A Continuous-Random-Network (CRN) model was used to generate the CAD data for the diamond-like amorphous structure, featuring a rod radius of 0.26d.
- Material Preparation: A photo-curable acrylic resin was mixed with 15 vol. % Alumina (Al2O3) powder (100 nm particle diameter) and 0.1 vol. % MgO powder (sintering aid).
- Scanning Laser Lithography: The CAD data was transferred to a URM-HP301 apparatus.
- Laser Source: He-Cd (λ = 325 nm).
- Laser Power/Speed: 5 ”W at 3 mm/s.
- Resolution: 15 ”m (xy-plane), 25 ”m (z-direction).
- Process: Layer-by-layer fabrication by xy-scanning the focused laser spot.
- Dewaxing: The fabricated structure was annealed at 873 K (600 °C) for 2 hours in air to remove the acrylic resin binder.
- Sintering: The structure was subsequently sintered at 2033 K (1760 °C) for 2 hours in air, converting the rods into porous alumina ceramic.
- Characterization: Terahertz time-domain spectroscopy (TAS7500SP) was used to measure transmittance and confirm PBG formation.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the potential of diamond-like structures for advanced THz control. However, the use of porous sintered alumina introduced significant scattering losses (Rayleigh scattering due to uneven surfaces and internal pores). 6CCVDâs high-purity MPCVD diamond offers a direct, high-performance solution to overcome these material limitations.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research with minimal loss and superior thermal stability, 6CCVD recommends the following materials:
| 6CCVD Material | Recommendation Rationale | Key Specifications |
|---|---|---|
| Optical Grade Single Crystal Diamond (SCD) | Highest purity, lowest intrinsic loss, and best thermal conductivity (2200 W/mK). Ideal for high-power THz applications requiring maximum transmission and minimal scattering. | SCD thickness: 0.1 ”m - 500 ”m. Ra < 1 nm polishing standard. |
| High-Purity Polycrystalline Diamond (PCD) | Excellent cost-to-performance ratio for large-area THz components. Superior to Alumina in thermal and mechanical properties. | PCD thickness: 0.1 ”m - 500 ”m. Wafers up to 125 mm diameter. |
| Boron-Doped Diamond (BDD) | If the application requires integrated conductive elements (e.g., THz emitters/detectors), BDD offers tunable conductivity while maintaining diamondâs structural integrity. | Custom doping levels available for specific resistivity requirements. |
Customization Potential
Section titled âCustomization PotentialâThe complexity of PAD structures requires precise material handling and post-processing capabilities, which 6CCVD provides in-house:
- Custom Substrate Dimensions: While the paper used small, millimeter-scale samples, 6CCVD can supply large-area SCD and PCD plates/wafers up to 125 mm in diameter, enabling scaling of THz devices. Substrate thickness is available up to 10 mm.
- Precision Polishing for Loss Reduction: The paper explicitly notes that Rayleigh scattering is caused by uneven rod surfaces and fine pores. 6CCVD guarantees ultra-smooth surfaces:
- SCD: Surface roughness Ra < 1 nm.
- Inch-size PCD: Surface roughness Ra < 5 nm.
- Benefit: Providing a pore-free, ultra-smooth diamond surface eliminates the primary sources of scattering loss observed in the sintered alumina.
- Advanced Metalization Services: If the PAD structure requires integrated electrodes or contacts for active tuning (e.g., applying voltage for bandgap modulation), 6CCVD offers internal metalization capabilities, including: Au, Pt, Pd, Ti, W, and Cu.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of MPCVD diamond for quantum, optical, and high-frequency applications. We offer consultation services to assist researchers in transitioning from ceramic prototypes to high-performance diamond components.
- Material Selection: Guidance on selecting the optimal diamond grade (SCD vs. PCD) based on required optical transparency, thermal load, and cost constraints for Terahertz Photonic Crystal projects.
- Design Optimization: Support for integrating diamond substrates into existing additive manufacturing workflows or advising on post-processing techniques (e.g., laser cutting, etching) to achieve the precise rod dimensions (0.17 mm) required for THz operation.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A recently proposed photonic bandgap material, named âphotonic amorphous diamondâ (PAD), was fabricated in a terahertz regime, and its terahertz-wave propagation properties were investigated. The PAD structure was fabricated from acrylic resin mixed with alumina powder, using laser lithographic, micro-additive manufacturing technique. After fabrication, the resulting structure was dewaxed and sintered. The formation of a photonic bandgap at around 0.45 THz was demonstrated by terahertz time-domain spectroscopy. Reflecting the disordered nature of the random network structure, diffusive terahertz-wave propagation was observed in the passbands; the scattering mean-free path decreased as the frequency approached the band edge. The mean-free paths evaluated at the band edges were close to the Ioffe-Regel threshold value for wave localization.