STRUCTURE OF POLYCRYSTALLINE DIAMOND COATINGS DEPOSITED BY СVD METHOD IN THE PLASMA OF GLOW DISCHARGE WITH THE USE OF PULSE POWER SUPPLY
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-04-07 |
| Authors | Konstantin Koshevoy, Yu.Ya. Volkov, V.E. Strel’nitskij, E.N. Reshetnyak |
| Institutions | Kharkiv Institute of Physics and Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research investigates the structure and quality of polycrystalline diamond (PCD) coatings synthesized via Chemical Vapor Deposition (CVD) using a magnetically stabilized Glow Discharge (GD) plasma driven by a novel pulsed power supply.
- Core Innovation: Replacement of the traditional DC power supply with a pulsed power source (50 kHz, Duty Cycle 1.1) significantly enhanced discharge stability, allowing for higher average power (2.5-3.0 kW) and increased productivity without risking arc transition.
- Quality Improvement: Grounding the substrate holder eliminated a high negative floating potential (present in previous DC designs), preventing accelerated ion bombardment and reducing structural defects.
- Structural Perfection: The use of the pulsed mode and substrate grounding resulted in diamond grains with Coherent Scattering Region (CSR) sizes up to 240 nm—approximately three times greater than those achieved with previous DC methods—indicating superior crystal perfection.
- Material Characteristics: Coatings were highly crystalline, pure polycrystalline diamond (Fm3m), with a lattice parameter (0.3565-0.3566 nm) nearly identical to natural diamond (0.35667 nm). No crystalline or amorphous graphite was detected.
- Texture Control: A map of deposition modes was established, demonstrating that crystal orientation (texture) can be precisely controlled between (100), (111), and (110) axes by adjusting the substrate temperature (Ts) and methane partial pressure (PCH4).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Deposition Method | CVD Glow Discharge | N/A | Stabilized by transverse magnetic field. |
| Power Supply Type | Pulsed (Tru Plasma Bios 4018) | N/A | Replaced DC supply for enhanced stability. |
| Pulse Frequency | 50 | kHz | Power supply setting. |
| Duty Cycle | 1.1 | N/A | Power supply setting. |
| Average Power | 2.5 - 3.0 | kW | During coating deposition. |
| Discharge Current | 3.5 - 4.5 | A | During coating deposition. |
| Total Pressure (Low) | 16 x 103 | Pa | Corresponds to 20-30 µm thickness. |
| Total Pressure (High) | 21 x 103 | Pa | Corresponds to 30-40 µm thickness. |
| Methane Content (CH4) | 1.5 - 3.0 | % | In H2-CH4 gas mixture. |
| Partial CH4 Pressure | 3.2 x 102 - 4.8 x 102 | Pa | Range investigated. |
| Substrate Temperature (Ts) | 955 - 1160 | °C | Measured by optical pyrometer “Promin”. |
| Coating Thickness | 20 - 40 | µm | Dependent on total pressure. |
| Crystal Lattice Parameter (a) | 0.3565 - 0.3566 | nm | Close to natural diamond (0.35667 nm). |
| CSR Size (Range) | 38 - 240 | nm | Coherent Scattering Regions (measure of perfection). |
| Crystal Size (Morphology) | 5 - 20 | µm | Observed via optical microscopy (well-defined faceting). |
| Optimal PCH4 for Max CSR | 3.2 x 102 | Pa | Achieved CSR size of 100-240 nm. |
Key Methodologies
Section titled “Key Methodologies”The polycrystalline diamond coatings were synthesized using a modified CVD glow discharge system stabilized by a transverse magnetic field.
- Equipment Setup: Utilized a combined disc cathode (Ø 115 mm) and a grounded substrate holder (Ø 52 mm). The DC power source was replaced by a pulsed power supply (Tru Plasma Bios 4018).
- Substrate Preparation: Monocrystalline silicon plates (111 orientation, 7.0x7.0x0.5 mm) were used. The surface was pre-treated (machined) with diamond powder ACM 2/3 to enhance nucleation.
- Plasma Activation: The H2-CH4 gas mixture was activated using the pulsed glow discharge (50 kHz, Duty Cycle 1.1) stabilized by a magnetic field, operating at 2.5-3.0 kW average power.
- Parameter Variation: Deposition was performed across a range of parameters:
- Total Pressure: 16 x 103 Pa and 21 x 103 Pa.
- Methane Content: 1.5% to 3.0% (Partial PCH4: 3.2 x 102 to 4.8 x 102 Pa).
- Substrate Temperature: 955 °C to 1160 °C.
- Structural Analysis: X-ray diffraction (DRON-3 apparatus, Cu anode, Bragg-Brentano scheme) was used to determine phase composition, lattice parameter, and CSR size (using the Selyakov-Scherrer formula).
- Texture Determination: Texture coefficients (Tc) were calculated based on reflection intensities to map the predominant crystal orientation as a function of Ts and PCH4.
- Morphology Analysis: Optical microscopy (MET-1) was used to examine the surface morphology and crystal faceting.
Commercial Applications
Section titled “Commercial Applications”The synthesis of high-quality, highly textured polycrystalline diamond films using a stable, high-power pulsed glow discharge CVD method is critical for applications requiring extreme material properties.
- Mechanical Engineering: Production of high-performance cutting tools, wear-resistant coatings, and dies due to diamond’s extreme hardness and low friction coefficient.
- Thermal Management: Use as heat spreaders and substrates in high-power electronics (e.g., RF and microwave devices) due to diamond’s exceptional thermal conductivity.
- Electronics and Optics: Fabrication of protective windows, optical components, and substrates for specialized electronics requiring chemical inertness and radiation resistance.
- Nuclear and High-Energy Physics: Coatings for components exposed to aggressive environments, high temperatures, and radiation fields.
- Biomedical Devices: Applications requiring biocompatibility and chemical inertness, such as medical implants or specialized sensors.
- Industrial Synthesis: Development of more cost-effective and scalable industrial synthesis technologies compared to complex microwave plasma systems, leveraging the stability and lower complexity of the pulsed glow discharge setup.
View Original Abstract
The structure of CVD carbon coatings synthesized in a hydrogen-methane mixture in the plasma of a glow discharge stabilized by a magnetic field using a pulsed power supply was studied by X-ray diffraction analysis and optical microscopy. The range of deposition parameters is determined, which ensure formation of polycrystalline diamond coatings. The coatings consist of diamond crystals with a clearly defined cut and the crystal lattice parameter close to the tabular value for natural diamond. The influence of the methane partial pressure in the gas mixture and the substrate temperature on the size and predominant orientation of diamond crystals in the coatings was determined. It is established that the use of the pulse mode and grounding of the substrate holder helps to improve the quality of diamond coatings.