Synthesis and Mechanism Study of Carbon Nanowires, Carbon Nanotubes, and Carbon Pompons on Single-Crystal Diamonds

At a Glance

Metadata	Details
Publication Date	2024-05-21
Journal	Crystals
Authors	Shuai Wu, Qiang Wang, Kesheng Guo, Lei Liu, Jie Bai
Institutions	Chongqing Jiaotong University, Ji Hua Laboratory
Citations	3
Analysis	Full AI Review Included

Technical Documentation: Synthesis of Diamond-Carbon Nanomaterial Heterostructures via MPCVD

Executive Summary

This research successfully demonstrates the selective, high-power Microwave Plasma Chemical Vapor Deposition (MPCVD) of diverse carbon nanomaterials (CNWs, CNTs, CPs) directly onto Single-Crystal Diamond (SCD) substrates. This achievement is highly relevant for engineers developing next-generation electronic and thermal management devices.

Novel Heterostructures: Achieved controllable growth of Carbon Nanowires (CNWs), Carbon Nanotubes (CNTs), and Carbon Pompons (CPs) on Type IIb CVD (100) SCD.
Selective Deposition Control: Growth morphology was precisely dictated by three key factors: Nitrogen (N₂) flow rate, substrate temperature (ranging 973 K to 1258 K), and substrate surface geometry (rectangular pits vs. flat surface).
Catalytic Mechanism: Molybdenum (Mo) thin films (150 nm) were utilized as effective catalysts for CNW and CNT growth, forming MoC intermediates.
High-Power MPCVD Advantage: The use of high-power MPCVD (up to 5 kW) in a butterfly-shaped resonant cavity ensures high plasma density and purity, mitigating contamination issues common in other CVD techniques.
Key Parameter Correlation: CNT formation was favored by higher N₂ flow (9 sccm) and slightly higher power/temperature compared to CNW formation (3 sccm N₂).
Structural Confirmation: TEM and Raman spectroscopy confirmed the distinct structures, including the solid nature of CNWs and the hollow structure of CNTs, and the presence of stress-induced blue-shifts.

Technical Specifications

The following hard data points were extracted from the experimental results detailing the synthesis conditions and resulting material properties.

Parameter	Value	Unit	Context
Substrate Material	Single Crystal Diamond (SCD)	N/A	Type IIb CVD (100) orientation
Substrate Dimensions	3 x 3	mm	Standard size used for all experiments
Catalyst Film Thickness	150	nm	Molybdenum (Mo) film for CNW/CNT growth
Microwave Frequency	2450	MHz	Standard industrial frequency
Operating Power Range	4.0 - 5.0	kW	Used for selective growth experiments
Operating Pressure Range	80 - 100	Torr	Used for selective growth experiments
Substrate Temperature (CP)	1258	K	Highest temperature, associated with pit position
Substrate Temperature (CNT)	993	K	Lowest temperature for CNT/CNW growth
N₂ Flow Rate (CNW)	3	sccm	Optimized for Carbon Nanowire growth
N₂ Flow Rate (CNT)	9	sccm	Optimized for Carbon Nanotube growth
CNW Average Diameter	80	nm	Solid structure confirmed by TEM
CNT Average Diameter	400	nm	Hollow structure confirmed by TEM
CP Average Diameter	20	µm	Grown in rectangular pits (1 mm x 1 mm x 1 µm)
Raman Diamond Peak (CNT)	1337	cm^-1	Blue-shifted due to internal stresses

Key Methodologies

The selective growth of carbon nanomaterials was achieved using a high-power MPCVD system coupled with precise control over gas composition, pressure, and substrate preparation.

Substrate Preparation:
- Used 3 x 3 mm Type IIb CVD (100) SCD substrates.
- Wet chemical cleaning (H₂SO₄/HNO₃ mixture at 473 K, followed by ultrasonic cleaning in deionized water, ethanol, and acetone).
- Experiments 1 and 2 utilized substrates with pre-fabricated rectangular pits (1 mm x 1 mm x 1 µm) to induce localized temperature differences (up to 323 K difference).
Catalyst Deposition (Experiments 3 & 4):
- A 150 nm thick Molybdenum (Mo) film was deposited directly onto the SCD surface via magnetron sputtering. Mo reacted with the carbon source to form MoC, acting as the active catalyst.
MPCVD Growth Parameters:
- Equipment: Butterfly-shaped resonant cavity MPCVD system capable of >10 kW power and up to 300 Torr pressure.
- Gas Precursors: Mixtures of Methane (CH₄), Hydrogen (H₂), and Nitrogen (N₂).
- Selective Growth Recipes:
  - CP/CNP (Expts 1 & 2): High H₂/CH₄ ratio (300/45 sccm), 5 kW power, 100 Torr pressure, 60 min duration.
  - CNW (Expt 3): Lower H₂/CH₄ ratio (200/45 sccm), 4 kW power, 80 Torr pressure, 3 sccm N₂ flow.
  - CNT (Expt 4): Lower H₂/CH₄ ratio (200/45 sccm), 4.5 kW power, 80 Torr pressure, 9 sccm N₂ flow.
Characterization:
- Optical Emission Spectroscopy (OES) monitored plasma species (C₂, CN, H_α).
- FE-SEM and TEM analyzed surface morphology and internal structure (solid CNW vs. hollow CNT).
- Confocal Laser Raman Microscopy confirmed crystal quality and defect presence (D and G bands).

6CCVD Solutions & Capabilities

This research validates the critical role of high-quality SCD substrates, precise metalization, and controlled MPCVD environments in fabricating complex diamond-carbon heterostructures. 6CCVD is uniquely positioned to supply the foundational materials and engineering support required to replicate and scale this research.

Applicable Materials

To replicate or extend the synthesis of CNW/CNT/CP heterostructures, researchers require high-ppurity, low-defect SCD substrates, which 6CCVD provides:

Single Crystal Diamond (SCD): The paper utilized Type IIb CVD (100) SCD. 6CCVD offers high-purity, low-defect SCD plates in (100), (110), and (111) orientations, essential for controlling epitaxial growth and minimizing unwanted nucleation sites.
Custom Substrate Geometry: The experiment relied on rectangular pits to induce localized temperature gradients. 6CCVD offers custom laser cutting and patterning services to create precise surface features, enabling tailored growth environments for selective deposition.
Polycrystalline Diamond (PCD): For applications where large area coverage is paramount, 6CCVD can provide high-quality PCD wafers up to 125mm in diameter, suitable for scaling up carbon nanomaterial deposition.

Customization Potential

The success of the CNW and CNT growth hinged on the 150 nm Molybdenum (Mo) catalyst film. 6CCVD offers comprehensive metalization services critical for catalyst preparation:

Research Requirement	6CCVD Capability	Technical Advantage
Catalyst Deposition	Custom Metalization: Au, Pt, Pd, Ti, W, Cu.	While Mo was used, 6CCVD’s expertise in refractory metal deposition (Ti, W) confirms the capability to deposit Mo or explore alternative catalysts (e.g., Fe/Ni/Co precursors via Ti/Pt/Au contact layers) for optimized growth.
Substrate Size	Plates/wafers up to 125mm (PCD).	The paper used 3x3 mm samples. 6CCVD enables scaling this research to production-relevant inch-size wafers for industrial applications.
Surface Finish	Polishing: Ra < 1nm (SCD), < 5nm (PCD).	High-quality polishing is crucial for uniform film deposition and minimizing non-epitaxial growth, ensuring consistent results across the substrate surface.
Thickness Control	SCD/PCD thickness from 0.1µm to 500µm.	Provides flexibility for optimizing thermal management layers or creating thick substrates (up to 10mm) for high-power device integration.

Engineering Support

The precise control of the MPCVD environment (gas flow, pressure, temperature) is complex. 6CCVD’s in-house PhD team specializes in diamond growth physics and can assist researchers and engineers in optimizing material selection for similar Diamond-Carbon Nanomaterial Heterostructure projects.

We offer consultation on:

Selecting the optimal SCD orientation and defect density for specific nanomaterial nucleation.
Designing multi-layer metalization stacks to enhance catalyst stability and adhesion.
Material specifications required for high-power, high-temperature MPCVD environments.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Carbon nanomaterials are in high demand owing to their exceptional physical and chemical properties. This study employed a mixture of CH4, H2, and N2 to create carbon nanostructures on a single-crystal diamond using microwave plasma chemical vapor deposition (MPCVD) under high-power conditions. By controlling the substrate surface and nitrogen flow rate, carbon nanowires, carbon nanotubes, and carbon pompons could be selectively deposited. The results obtained from OES, SEM, TEM, and Raman spectroscopy revealed that the nitrogen flow rate and substrate surface conditions were crucial for the growth of carbon nanostructures. The changes in the plasma shape enhanced the etching effect, promoting the growth of carbon pompons. The CN and C2 groups play vital catalytic roles in the formation of carbon nanotubes and nanowires, guiding the precipitation and composite growth of carbon atoms at the interface between the Mo metal catalysts and diamond. This study demonstrated that heterostructures of diamond-carbon nanomaterials could be produced under high-power conditions, offering a new approach to integrating diamond and carbon nanomaterials.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst14060481

References

2017 - From graphite to graphene oxide and graphene oxide quantum dots [Crossref]
2024 - On the vibrational behavior of the conventional and hetero-junction carbon nanotubes [Crossref]
2024 - High-performance carbon nanofiber conductive films induced by titanium carbide [Crossref]
2023 - Carbon nanosphere synthesis and applications for rechargeable batteries [Crossref]
2019 - Fabrication of a spherical superstructure of carbon nanorods [Crossref]
2022 - Fullerene, fullerane and the fulleryne: A comparative thermodynamic study for a new member of the carbon cage family [Crossref]
2019 - Preparation and microwave absorption properties of magnetic carbon nano-onion matrix composites [Crossref]
2021 - Nanoengineering of Advanced Carbon Materials for Sodium-Ion Batteries [Crossref]
2019 - Preparation and characterisation of carbon spheres for carbon dioxide capture [Crossref]