Low-pressure diamond - from the unbelievable to technical products
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-03-16 |
| Journal | ChemTexts |
| Authors | Roland Haubner |
| Institutions | TU Wien |
| Citations | 21 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Low-Pressure CVD Diamond
Section titled âTechnical Documentation & Analysis: Low-Pressure CVD DiamondâSource Paper: Haubner, R. (2021). Low-pressure diamond: from the unbelievable to technical products. ChemTexts.
Executive Summary
Section titled âExecutive SummaryâThis review confirms the industrial maturity of Chemical Vapor Deposition (CVD) diamond, highlighting its superior properties for demanding technical applications. 6CCVD leverages Microwave Plasma CVD (MPCVD) to meet the stringent requirements identified in this research.
- High Purity & Thermal Management: MPCVD is the preferred method for producing high-purity diamond layers essential for optical windows and high thermal conductivity heat spreaders (up to 10 ”m/h growth rates reported).
- Morphology Control: Diamond morphology (faceted SCD, polycrystalline PCD, or ballas) is critically controlled by the ratio of atomic hydrogen (at.H) to carbon concentration, allowing precise engineering of surface properties.
- Doping for Functionality: Boron doping (BDD) is established for p-type semiconducting and electrochemical applications (e.g., wastewater treatment), requiring precise control of B/C ratios (1000-5000 ppm range).
- Wear Applications: Hot-Filament CVD (HFCVD) is suitable for wear-resistant coatings, although the resulting diamond typically contains filament impurities (W, Ta). 6CCVD offers high-quality PCD alternatives.
- Substrate Engineering: Successful deposition, especially on hardmetals (WC-Co), requires complex substrate pre-treatment (etching, intermediate layers, or surface reactions) to manage carbon diffusion and cobalt migration.
- Industrial Scale & Quality: CVD diamond synthesis has reached industrial production, necessitating suppliers like 6CCVD who can provide custom dimensions, high-quality polishing (Ra < 1nm), and precise material specifications (SCD, PCD, BDD).
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters are critical for controlling the growth and quality of low-pressure CVD diamond, as extracted from the review:
| Parameter | Typical Value | Unit | Context / Implication |
|---|---|---|---|
| MPCVD Growth Rate | > 10 | ”m/h | High-purity diamond, suitable for thick layers. |
| HFCVD Growth Rate | ~1 | ”m/h | Lower rate, primarily used for wear coatings. |
| Substrate Temperature (Tsub) | 600 - 1000 | °C | Must be below 1000 °C to prevent graphitization; above 600 °C for reasonable deposition speed. |
| Filament Temperature (TFil) | 2200 - 2500 | °C | Used in HFCVD to generate atomic hydrogen (at.H). |
| Characteristic Raman Peak | 1332 | cm-1 | Confirms diamond crystal lattice structure. |
| Boron Doping (Gas Phase) | 1000 - 5000 | ppm B/C | Concentration range that decreases growth rate but enables BDD functionality. |
| Boron Incorporation (SCD) | Up to 3 | at.% | Incorporated in (111) growth sectors. |
| Required at.H Concentration | High | % | Necessary to selectively etch sp2 graphite and permit diamond (sp3) growth. |
Key Methodologies
Section titled âKey MethodologiesâThe research highlights several established methods for low-pressure diamond synthesis, all relying on the generation and transport of atomic hydrogen (at.H) to the substrate surface.
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Gas Activation and Precursors:
- Hydrogen (H2) and carbon-containing gases (e.g., CH4, acetone, ethanol) are used.
- Atomic hydrogen (at.H) is generated via high temperature (HFCVD) or gas plasma (MPCVD, DC-Glow Discharge).
- The C/H/O ratio is the main parameter optimized for diamond domain growth versus graphite/amorphous carbon deposition.
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Primary Deposition Methods:
- Hot-Filament CVD (HFCVD): Uses W or Ta filaments (up to 2500 °C). Simple design, easy up-scaling, but results in lower growth rates (~1 ”m/h) and filament contamination (impurities).
- Microwave Plasma CVD (MPCVD): Uses microwave power to generate plasma. Produces high-purity diamond, high growth rates (> 10 ”m/h), and allows easy temperature regulation. Preferred for optical and thermal applications.
- Plasma Jets (DC/Arc): Allows high-speed growth on relatively large surfaces, but requires controlled substrate cooling due to high temperatures.
- DC-Glow Discharge: Offers high growth rates but faces challenges with scale-up and reproducibility.
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Growth Control and Quality:
- Diamond quality is primarily influenced by the ratio of at.H to carbon and the substrate surface temperature (Tsub).
- Doping elements (B, N, P) are introduced into the gas phase to achieve specific electrical or structural properties (e.g., BDD for p-type semiconductor/electrodes).
- Substrate pre-treatment (e.g., etching Co from WC-Co hardmetals, or seeding with nano-diamond) is critical for nucleation density and layer adhesion.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate and extend the research findings detailed in this review, offering superior purity, customization, and scale.
Applicable Materials for Research Replication
Section titled âApplicable Materials for Research Replicationâ| Application Area (from Paper) | 6CCVD Material Recommendation | Key 6CCVD Capability Match |
|---|---|---|
| Optical Windows / High Transparency | Optical Grade SCD (Single Crystal Diamond) | SCD thickness up to 500 ”m. Polishing to Ra < 1 nm for minimal scattering and highest transparency. |
| High Thermal Conductivity (Heat Spreaders) | High Purity SCD (Low Nitrogen/Defect Density) | Precise MPCVD control ensures low impurity levels, maximizing thermal conductivity (as required by [92, 186, 187]). |
| Electrochemical Applications (Wastewater) | Heavy Boron Doped Diamond (BDD) | Custom BDD synthesis to achieve high conductivity and the large electrochemical window necessary for efficient electrode performance. |
| Wear-Resistant Coatings / Tooling | High-Quality PCD Wafers | Custom dimensions up to 125 mm diameter (PCD) and thickness up to 500 ”m, providing binder-free, high-wear resistance alternatives to HFCVD coatings. |
Customization Potential
Section titled âCustomization PotentialâThe review emphasizes that successful diamond integration often relies on managing substrate interactions and achieving precise dimensions. 6CCVD offers comprehensive customization services:
- Custom Dimensions and Thickness: We provide SCD and PCD plates/wafers up to 125 mm in diameter, with thicknesses ranging from 0.1 ”m to 500 ”m, enabling the production of both thin films and robust free-standing layers.
- Advanced Polishing: For optical and thermal applications, 6CCVD guarantees ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, crucial for minimizing defects and maximizing performance.
- Integrated Metalization Services: The paper highlights the use of various metals (Ti, W, Mo, Pt, Pd) for interlayers or contacts. 6CCVD offers internal, high-quality metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to integrate contacts or adhesion layers directly onto the diamond surface.
- Substrate Supply: We can supply custom diamond substrates (up to 10 mm thick) for epitaxial growth experiments, supporting research into large-area single crystalline diamond synthesis (as reported by Schreck [140]).
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in non-equilibrium CVD kinetics and material science. We offer authoritative professional support for projects involving:
- Doping Optimization: Assistance in selecting the correct B/C or N/C ratios to achieve desired electrical or structural properties for semiconducting or electrochemical projects.
- Morphology Control: Consultation on MPCVD parameters (pressure, temperature, gas flow) to achieve specific crystal habits, ranging from highly faceted (100) or (111) SCD to fine-grained NCD/UNCD structures.
- Adhesion and Interlayers: Guidance on material selection and processing for intermediate layers to ensure robust adhesion on challenging substrates like hardmetals or ferrous alloys, addressing the complex interactions described in Fig. 16 and Fig. 18.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The idea to grow diamond from the gas phase was born in the 1950s but it took about 30 years until first diamond layers directly grown from the gas phase on substrates were shown in Japan by Matsumoto and co-workers. During the first years of research the function of atomic hydrogen, various growth methods and process parameters were investigated. Research was primarily focused on applications for wear-resistant tools. For this topic the interactions of substrates like hardmetals and ceramics, with diamond deposition gas atmosphere, were investigated. Beside its superior hardness, diamond exhibits the highest heat conductivity, high transparency, high chemical inertness and suitable semiconducting properties. The various requirements for the areas of application of diamond required a division of diamond research into corresponding sub-areas. The hot-filament method is used mainly for wear applications, because it is highly suited to coat complex geometries, but the diamond contains some impurities. Another method is the microwave plasma system which allows the growth of pure diamond used for optical windows and applications requiring high thermal conductivity. Other research areas investigated include doped diamond for microelectronic or electrochemical applications (e.g. waste water treatment); ballas (polycrystalline, spherical diamond), NCD (nanocrystalline diamond) and UNCD (ultra-nanocrystalline diamond) for wear applications. It should be noted that CVD (chemical vapour deposition) diamond synthesis has reached the stage of industrial production and several companies are selling different diamond products. This work is intended to convey to the reader that CVD diamond is an industrially manufactured product that can be used in many ways. With correspondingly low costs for this diamond, new innovative applications appear possible.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1971 - Physical-chemical synthesis of diamond from vapor phase