Oxidation Etching Mechanism of Boron-Doped CVD Polycrystalline Diamond Films
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-01 |
| Journal | Journal of The Surface Finishing Society of Japan |
| Authors | Haisheng Song, H. Kanda, Osamu Fukunaga, Hitoshi Sumiya, Sadao Takeuchi |
| Institutions | Nippon Institute of Technology, National Institute for Materials Science |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the mechanism by which boron doping enhances the oxidation resistance of polycrystalline Chemical Vapor Deposition (CVD) diamond films, a critical factor for high-temperature applications.
- Core Achievement: Boron-doped diamond (BDD) films exhibited significantly superior oxidation resistance compared to non-doped diamond (NDD) films when heated in air at 825 °C.
- Failure Mode Mitigation: NDD films showed severe etching, particularly at grain boundaries and crystal faces, while BDD films maintained their morphology with only slight etching traces.
- Mechanism Identification: Surface analysis (AES and XPS) of the BDD film after heating confirmed the presence of boron oxide (B2O3) on the surface.
- Protective Layer Hypothesis: It is proposed that during heating, the diamond carbon oxidizes and is removed, leaving behind boron which reacts with oxygen to form B2O3.
- Functionality: This B2O3 layer acts as a stable, protective film, suppressing further oxidation of the underlying diamond lattice and leading to high chemical wear resistance.
- Synthesis Method: Films were synthesized using the Hot Filament CVD (HFCVD) method on commercial cemented carbide substrates (K10 equivalent).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Oxidation Test Temperature | 825 | °C | Maximum temperature held for 1 hour in air. |
| Heating Rate | 50 | °C/min | Rate used during ramp-up to 825 °C. |
| Synthesis Time | 480 | h | Duration for polycrystalline film growth. |
| Average Grain Size | 30 | ”m | Size of synthesized polycrystalline diamond. |
| Film Thickness | 200 | ”m | Thickness of synthesized diamond film. |
| Synthesis Pressure | 6.66 | kPa | HFCVD chamber pressure. |
| Hydrogen Flow Rate | 150 | cc/min | Carrier gas flow rate. |
| Methane Concentration | 1 | % | CH4 concentration relative to H2. |
| Boron Concentration (BDD) | 3000 | ppm | Boron concentration relative to Carbon source (using Trimethylboron). |
| B2O3 XPS Peak Location | 192 | eV | Peak confirming boron oxide formation after heating. |
| B/B4C XPS Peak Location | 186 | eV | Peak confirming residual boron/boron carbide after heating. |
| Carbon (C) AES Peak Location | 272 | eV | Detected before heating. |
| Boron (B) AES Peak Location | 182 | eV | Detected after heating (before Ar bombardment). |
| Oxygen (O) AES Peak Location | 512 | eV | Detected after heating (before Ar bombardment). |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized Hot Filament CVD (HFCVD) for film synthesis and subsequent thermal and surface analysis techniques to determine the oxidation mechanism.
- Substrate Preparation: Commercial K10 equivalent cemented carbide cutting tips were mirror-polished and subjected to seeding/nucleation treatment to facilitate the growth of freestanding diamond films.
- BDD Synthesis: Polycrystalline diamond films were grown using HFCVD. Methane (CH4) was the carbon source (1% concentration in H2), and Trimethylboron {B(CH3)3} was used to supply 3000 ppm Boron relative to Carbon.
- Oxidation Testing: Diamond films were cleaved into 2-4 mm pieces and heated in an electric furnace (SUPER 100T) in an ambient air atmosphere. The temperature was ramped at 50 °C/min to 825 °C, held for 1 hour, and then slowly cooled.
- Morphological Analysis: Scanning Electron Microscopy (SEM, JSM-IT300LA) was used to observe the surface morphology of NDD and BDD films before and after the 825 °C heating process.
- Elemental Analysis: Auger Electron Spectroscopy (AES, JAMP-7830F) was performed to identify surface elements before and after heating. Argon (Ar) bombardment was used to remove the surface layer and confirm the depth profile of the oxidation products.
- Chemical State Analysis: X-ray Photoelectron Spectroscopy (XPS, JPS-9030) was used to determine the chemical bonding states of Boron on the surface, confirming the presence of B2O3 (192 eV peak) and residual B/B4C (186 eV peak).
Commercial Applications
Section titled âCommercial ApplicationsâThe enhanced thermal and chemical stability provided by boron doping is crucial for extending the lifetime and performance of diamond materials in demanding industrial environments.
- High-Performance Cutting Tools: Polycrystalline diamond (PCD) tools, especially those used for high-speed machining of ferrous alloys or composites, benefit from BDDâs resistance to chemical wear (oxidation) at elevated cutting temperatures.
- High-Temperature Sensors and Electronics: Diamond is utilized in high-power electronics and heat sinks. BDD improves the reliability and operational lifespan of these devices when exposed to oxidizing atmospheres above 600 °C.
- Wear and Friction Components: Applications requiring extreme hardness and stability, such as bearings, seals, and dies, where friction generates localized heat leading to oxidative degradation.
- Electrochemistry: BDD is a widely used electrode material (BDD electrodes). Improved oxidation resistance enhances the stability and longevity of these electrodes in aggressive chemical environments used for water treatment or synthesis.
- Protective Coatings: BDD films can serve as protective coatings for materials operating in harsh, high-temperature, oxidizing environments where conventional diamond would rapidly degrade.