| Metadata | Details |
|---|
| Publication Date | 2022-11-27 |
| Journal | Coatings |
| Authors | Jiadong Shi, Xurui Feng, Yabo Huang, Yuting Zheng, Liangxian Chen |
| Institutions | University of Science and Technology Beijing |
| Citations | 8 |
| Analysis | Full AI Review Included |
- Robust All-Carbon Composite: A novel Microwave Plasma Chemical Vapor Deposition (MPCVD) method was successfully used to grow dense, multi-walled Carbon Nanotubes (CNTs) directly onto polished CVD diamond substrates, creating a highly stable, all-carbon composite structure.
- Superior Adhesion: The CNT-diamond interface exhibited significantly stronger adhesion forces compared to CNTs grown on standard silicon (Si) substrates, confirmed via 24-hour ultrasonication and quantitative nanoscratch testing.
- Anchoring Mechanism: The enhanced bonding is attributed to the formation of a unique carbon transition layer (approximately 6 nm thick) at the interface, resulting from the mutual reaction between Ni catalyst and diamond during annealing.
- Catalyst Pinning: Ni catalyst nanoparticles are immersed and anchored within this transition layer, effectively pinning them to the diamond surface and promoting a stable base-growth mechanism for the CNTs.
- High Structural Quality: The resulting multi-walled CNTs (15 nm diameter, ~10 walls) demonstrated high graphitization quality, evidenced by a low Raman intensity ratio (ID/IG = 0.89) on the diamond substrate.
- Low-Temperature Synthesis: CNT growth was achieved at a relatively low temperature (600 °C), significantly below the pyrolysis temperature of methane, enabled by the microwave plasma generating active carbon radicals (C2 and CH).
| Parameter | Value | Unit | Context |
|---|
| Substrate Material | CVD Diamond, Si | - | Self-standing, polished wafers |
| Substrate Roughness (Ra) | < 10 | nm | Polished diamond surface |
| Catalyst Material | Nickel (Ni) | - | Sputtered layer |
| Initial Ni Thickness | 10 | nm | Deposited via magnetron sputtering |
| Ni Sputtering Temperature | 200 | °C | Catalyst deposition |
| Annealing Temperature | 550 | °C | Catalyst activation in H2 atmosphere |
| Annealing Time | 5 | min | Catalyst activation |
| CNT Growth Temperature | 600 | °C | Microwave Plasma CVD (MPCVD) |
| CNT Growth Time | 30 | min | MPCVD duration |
| Microwave Power (Growth) | 1100 | W | System output power |
| Chamber Pressure (Growth) | 3.0 | kPa | Reaction environment |
| Carbon Source Gas Ratio | CH4:H2 = 1:9 | Ratio | Carbon source and carrier gas |
| Resulting CNT Structure | Multi-walled | - | Approximately 10 walls |
| CNT Diameter | ~15 | nm | Measured tube size |
| CNT Layer Thickness | 0.9-1 | ”m | Measured via cross-sectional SEM |
| Transition Layer Thickness | ~6 | nm | Observed at CNT-Diamond interface |
| CNT Quality (Diamond) | 0.89 | ID/IG | Raman intensity ratio (measure of graphitization) |
| Nanoscratch Load | 500 | ”N | Constant normal load for adhesion test |
- Substrate Preparation: CVD diamond plates were mechanically polished to achieve a smooth surface (Ra < 10 nm). Si wafers of the same size were used as control substrates.
- Catalyst Deposition: A 10 nm thick Ni catalytic layer was deposited onto both diamond and Si substrates using high-vacuum multi-target magnetron sputtering (200 °C, 70 W power).
- Catalyst Annealing (Stage I): The substrates were placed in the MPCVD system and annealed at 550 °C for 5 minutes under a pure H2 atmosphere, converting the Ni film into active Ni nanoparticles via Oswald ripening.
- CNT Growth (Stage II): CNTs were synthesized via MPCVD at 600 °C for 30 minutes, using a CH4:H2 gas mixture (1:9 ratio) at 3.0 kPa pressure and 1100 W microwave power.
- Plasma Diagnosis: Optical Emission Spectroscopy (OES) was utilized during growth to confirm the presence of active carbon radicals (C2 and CH) generated by the microwave dissociation of CH4.
- Structural Characterization: Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to analyze morphology and interface structure. Focused Ion Beam (FIB) preparation was necessary for cross-sectional TEM analysis.
- Adhesion Quantification: Adhesion strength was evaluated qualitatively using 24-hour ultrasonic vibration tests and quantitatively using nanoscratch tests (500 ”N normal load) to measure the lateral force required for detachment.
- Thermal Interface Materials (TIMs): The CNT-diamond composite is ideal for high-performance TIMs, leveraging the ultra-high thermal conductivity of diamond combined with the efficient heat transfer pathways provided by the vertically aligned CNTs, crucial for advanced chip cooling.
- High-Intensity Optical Coatings: The CNT coating acts as a highly efficient black body absorber, suitable for high-radiation or high-intensity endothermic coatings in aerospace or sensor applications.
- Robust Microelectronics: The strong, chemically bonded interface ensures mechanical stability, making the composite suitable for durable micro electromechanical systems (MEMS) and field emission devices (EFE) that require long-term reliability under stress.
- High-Power Devices: The combination of diamond (high electrical resistivity) and CNTs (high thermal conductivity) creates a promising substrate for high-power electronic devices where efficient heat dissipation without electrical leakage is necessary.
- Catalyst Stability: The anchoring mechanism of the Ni catalyst within the transition layer offers a pathway for developing highly stable, reusable carbon-based catalysts where catalyst particle migration must be minimized.
View Original Abstract
In this paper, we present a novel method for growing carbon nanotubes (CNTs) via microwave plasma chemical vapor deposition (MPCVD) on diamond and silicon substrates. Scanning electron microscopy (SEM) and Raman spectroscopy analyses revealed dense, multi-walled carbon nanotubes growing on the diamond substrate. Optical Emission Spectroscopy (OES) showed that in the process of growing carbon nanotubes with the MPCVD method, the CH4 introduced into the system is excited by microwaves and dissociated to form active radicals such as C2 and CH, which are considered the C source of the synthesized carbon nanotube. Observation with high-resolution transmission electron microscopy (HRTEM) showed that most Ni catalyst nanoparticles that catalyze the growth of carbon nanotubes are located close to the diamond surface. In contrast, on the Si substrate, Ni catalyst nanoparticles were randomly distributed. A unique transition layer was observed between the diamond and carbon nanotubes, with the Ni particles being immersed into this transition layer and acting as anchors to fix the carbon nanotubes, resulting in a robust connection between the diamond and the CNT coating.
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