Growth of Carbon Nanotubes on Diamond with a Robust Structural Connection via Microwave Plasma Chemical Vapor Deposition

At a Glance

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

Technical Documentation & Analysis: Robust CNT Growth on MPCVD Diamond

Executive Summary

This document analyzes the successful fabrication of a high-adhesion Carbon Nanotube (CNT) coating on a Microwave Plasma Chemical Vapor Deposition (MPCVD) diamond substrate. This research validates diamond as the superior substrate for CNT composites, particularly for high-performance thermal and optical applications.

Robust Composite Achieved: Multi-walled CNTs were successfully grown on CVD diamond using MPCVD, resulting in a stable, all-carbon composite structure.
Superior Adhesion: Ultrasonication and nanoscratch tests confirmed that the CNT-diamond adhesion force is significantly stronger (Lateral Force Increase: ~1300 µN) compared to CNTs grown on standard Si substrates.
Mechanism Identified: The strong bonding is attributed to the formation of a unique 6 nm thick carbon transition layer at the diamond interface, which chemically anchors the Ni catalyst nanoparticles (base-growth mechanism).
High Material Quality: The resulting CNTs exhibited high structural integrity, characterized by a low Raman I_D/I_G ratio of 0.89.
Critical Application Potential: The composite is highly promising for advanced thermal management (chip cooling) and high-intensity endothermic/high-radiation black coatings, leveraging diamond’s exceptional thermal properties.
Methodology Validation: The study confirms that standard MPCVD techniques, combined with precise Ni catalyst deposition, are effective for creating high-quality, strongly bonded CNT-diamond interfaces.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Diamond Substrate Type	Self-standing CVD	N/A	Prepared via DC Arc Plasma Jet CVD
Substrate Dimensions (Final)	10 x 8 x 0.5	mm	Used for CNT growth comparison
Substrate Surface Roughness (Ra)	< 10	nm	Achieved via automatic polishing
Ni Catalyst Layer Thickness	10	nm	Deposited via magnetron sputtering
Ni Sputtering Temperature	200	°C	Catalyst deposition process
Thermal Annealing Temperature (Stage I)	550	°C	Conversion of Ni film to nanoparticles
Thermal Annealing Time (Stage I)	5	min	Performed in pure H₂ atmosphere
CNT Growth Temperature (Stage II)	600	°C	Microwave Plasma CVD process
CNT Growth Time	30	min	Duration of CNT synthesis
Carbon Source Ratio (CH₄:H₂)	1:9	Ratio	Gas mixture for active radical generation
Growth Chamber Pressure	3.0	kPa	During CNT synthesis
CNT Structure	Multi-walled	N/A	Approximately 10 walls
CNT Diameter	~15	nm	Measured via HRTEM
CNT Quality (I_D/I_G Ratio)	0.89	Ratio	Raman spectroscopy on Diamond substrate
Interfacial Transition Layer Thickness	~6	nm	Graphite region between CNTs and Diamond
CNT-Diamond Adhesion Force Increase	~1300	µN	Measured via Nanoscratch Test (Lateral Force)

Key Methodologies

The CNT-diamond composite was fabricated using a multi-stage process centered around MPCVD and magnetron sputtering:

Diamond Substrate Preparation: A 3-inch self-standing CVD diamond plate was prepared (likely Polycrystalline Diamond, PCD). The plate was flattened and polished to achieve an average surface roughness (Ra) of less than 10 nm.
Catalyst Deposition: A high-vacuum multi-target magnetron sputtering system was used to deposit a 10 nm thick Ni layer onto the diamond substrate at 200 °C, using 70 W power and 0.5 Pa chamber pressure.
Catalyst Thermal Annealing (Stage I): The Ni-coated diamond was placed in the MPCVD system under a pure H₂ atmosphere. The sample surface temperature was raised to 550 °C for 5 minutes (Microwave Power: 1000 W; Pressure: 2.7 kPa) to convert the continuous Ni film into uniformly distributed Ni nanoparticles (Oswald ripening).
CNT Growth (Stage II): The carbon source (CH₄) mixed with H₂ (1:9 ratio) was introduced. Microwave energy excited the gas, generating active carbon radicals (C₂ and CH).
Growth Parameters: CNT growth occurred at a surface temperature of 600 °C for 30 minutes (Microwave Power: 1100 W; Pressure: 3.0 kPa).
Interface Analysis: HRTEM and EDS confirmed the formation of a 6 nm carbon transition layer, resulting from the reaction between Ni and the diamond substrate during annealing, which provided the robust anchor for the CNTs (base-growth mechanism).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality diamond substrates and specialized fabrication services required to replicate and advance this critical research into robust CNT-diamond composites.

Applicable Materials

To replicate the high-performance substrate used in this study, 6CCVD recommends the following materials:

Optical Grade SCD (Single Crystal Diamond): For applications requiring the highest thermal conductivity (up to 2200 W/mK) and lowest defect density, ensuring optimal interface quality and thermal transfer.
High-Purity PCD (Polycrystalline Diamond): Cost-effective solution for large-area applications (up to 125mm wafers) requiring high thermal conductivity and mechanical robustness.
Polishing Specification: We guarantee SCD substrates with Ra < 1 nm and inch-size PCD substrates with Ra < 5 nm, significantly exceeding the Ra < 10 nm requirement of the paper, ensuring superior surface quality for uniform catalyst nucleation.

Customization Potential

The successful integration of CNTs relies heavily on precise substrate preparation and catalyst control. 6CCVD offers comprehensive services to meet these needs:

Research Requirement	6CCVD Customization Capability
Custom Dimensions	We supply plates/wafers up to 125mm (PCD) and offer precision laser cutting to produce custom geometries (e.g., 10 x 8 x 0.5 mm sections) or substrates up to 10 mm thick.
Catalyst Deposition	The paper utilized a 10 nm Ni layer. 6CCVD provides in-house metalization services, including Ni, Ti, Pt, Au, Pd, W, and Cu, allowing researchers to precisely tune catalyst thickness and composition for optimized CNT growth mechanisms (tip-growth vs. base-growth).
Interface Engineering	We can supply substrates pre-treated with specific surface terminations (e.g., hydrogen or oxygen termination) to influence the initial Ni-C reaction and control the formation of the critical 6 nm transition layer.
Global Logistics	We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials directly to your lab.

Engineering Support

This research highlights the potential of CNT-diamond composites for High-Performance Thermal Interfaces and High-Radiation Black Coatings.

6CCVD’s in-house PhD team of material scientists can assist with:

Material Selection: Optimizing the choice between SCD and PCD based on thermal budget, size constraints, and cost targets for similar thermal management projects.
Process Integration: Consulting on the optimal MPCVD parameters (gas ratios, temperature profiles) for maximizing CNT adhesion and structural integrity on 6CCVD substrates.
Interface Characterization: Providing substrates with certified surface quality and metalization uniformity, reducing experimental variability in catalyst studies.

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

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.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings12121838

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