Boron-doped diamond growth on carbon fibre - Enhancing the electrical conductivity

At a Glance

Metadata	Details
Publication Date	2023-01-08
Journal	Applied Surface Science
Authors	Josué Millán-Barba, Hicham Bakkali, Fernando Lloret, M. Gutiérrez, Roberto Guzmán de Villoria
Institutions	Foundation for the Research Development and Application of Composite Materials, Universidad de Cádiz
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron-Doped Diamond for Enhanced Electrical Conductivity in Carbon Fiber Composites

This document analyzes the research paper “Boron-doped diamond growth on carbon fibre: Enhancing the electrical conductivity” (Applied Surface Science 615, 2023) and outlines how 6CCVD’s specialized Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) diamond products and services can support and extend this critical research area.

Executive Summary

This study successfully demonstrates the use of heavily Boron-Doped Diamond (BDD) coatings applied via MPCVD to Carbon Fibres (CF) to significantly enhance the electrical conductivity of composite materials, addressing a major weakness in Carbon Fibre Reinforced Polymers (CFRP).

Core Achievement: Successful deposition of heavily Boron-Doped Diamond (BDD) onto commercial PAN-based Carbon Fibres (CF) to form a rigid, conductive core-shell structure.
Electrical Enhancement (Macro): Kelvin macro-measurements showed that the BDD coating decreased the electrical resistance of the CF tow by up to 5 times, reducing resistivity by half compared to uncoated CF.
Electrical Enhancement (Local): Micro-measurements (C-AFM) confirmed an order of magnitude increase in local surface electrical conductivity on the BDD-coated CF filaments.
Material Properties: The BDD layers exhibited metallic behavior, with estimated electrical conductivity exceeding 10³ Ω^-1 mm^-1.
Doping Level: Boron concentration was confirmed via Raman spectroscopy to be in the heavily doped, metallic regime, ranging from 2 x 10²¹ cm^-3 to 5 x 10²¹ cm^-3.
Structural Impact: The BDD coating thickness was optimized between 69 nm and 104 nm, successfully filling the grooves of the original CF and reducing surface roughness (Ra) from 12 nm to 9 nm.
Application Potential: This methodology promises to improve the transverse conductivity and reduce electrical anisotropy in CFRP, opening new applications in aerospace, structural, and biomedical fields.

Technical Specifications

The following hard data points were extracted from the research paper detailing the material properties and growth parameters of the BDD films.

Parameter	Value	Unit	Context
BDD Electrical Conductivity (Estimated)	> 10³	Ω^-1 mm^-1	Derived from Kelvin method and Raman analysis
Boron Concentration Range	2 x 10²¹ to 5 x 10²¹	cm^-3	Heavily doped, metallic regime confirmed by Raman Fano effect
BDD Layer Thickness (Range)	69 to 104	nm	Measured via SEM on cross-sections
Uncoated CF Surface Roughness (Ra)	12	nm	Measured via C-AFM
BDD-Coated CF Surface Roughness (Ra)	9	nm	Measured via C-AFM, indicating surface smoothing
MPCVD Power Range	3.0 to 4.0	kW	ASTEX 6500 reactor conditions
MPCVD Pressure Range	35 to 45	Torr	Growth conditions
C-AFM Current Response (BDD-CF Peak)	2.08	µA	Order of magnitude higher than uncoated CF (0.36 µA)
CF Substrate Diameter	6.9	µm	Nominal diameter of HexTow AS7 filaments

Key Methodologies

The experiment relied on precise MPCVD control and advanced nanoscale characterization techniques to confirm the material quality and electrical performance.

Substrate Pre-treatment: Commercial PAN-based Carbon Fibres (CF) were pre-treated by immersion in an ultrasonic bath containing 6-7 nm diamond nanoparticles in deionized water to enhance nucleation density.
MPCVD Deposition: Boron-Doped Diamond (BDD) was grown using an ASTEX 6500 MPCVD reactor.
Gas Composition Control: The gas mixture consisted of Methane (CH₄), Hydrogen (H₂), and Trimethylborane (TMB). TMB flow (40-100 sccm) was the primary control mechanism for achieving high boron doping levels (BDD metallic regime).
Macro Electrical Measurement (Kelvin Method): A two-wire setup was used on CF tows of varying lengths to measure resistance and calculate the longitudinal electrical conductivity of the bulk material.
Micro Electrical Measurement (C-AFM): Conductive Atomic Force Microscopy was performed on single filaments at a sample bias of +500 mV using conductive diamond-coated tips (CDT-NCHR) to map local surface current density.
Cross-Sectional Analysis (sMIM/AFM): Scanning Microwave Impedance Microscopy (sMIM) was used on polished cross-sections of CF embedded in epoxy resin to qualitatively map the relative electrical conductivity of the three components: resin, CF core, and BDD coating.
Material Characterization (Raman Spectroscopy): Room-temperature Raman spectra confirmed the diamond phase (sp³ peak at 1332 cm^-1) and quantified the boron concentration (2-5 x 10²¹ cm^-3) using the Fano effect analysis and the characteristic boron band at 1200 cm^-1.

6CCVD Solutions & Capabilities

This research highlights the critical need for highly controlled, heavily doped diamond materials for advanced composite and electronic applications. 6CCVD is uniquely positioned to supply the necessary BDD materials and engineering support to replicate, scale, and extend this research.

Applicable Materials

To achieve the metallic conductivity and thin-film requirements demonstrated in this paper, 6CCVD recommends the following specialized materials:

6CCVD Material Solution	Specification Match	Application Relevance
Heavy Boron-Doped PCD (Polycrystalline Diamond)	Required metallic conductivity (10²¹ cm^-3 range) and polycrystalline structure for coating applications.	Ideal for high-performance electrodes, conductive heat spreaders, and large-area composite tooling.
Nanocrystalline Diamond (NCD) Films	The paper utilized nanocrystalline growth (NCD) to achieve conformal coating on the CF surface.	6CCVD offers NCD films with superior uniformity and tunable grain size for optimal surface coverage and roughness control.
Ultra-Thin SCD/PCD Plates	Required film thickness was 69-104 nm.	We provide SCD and PCD films with thickness control down to 0.1 µm (100 nm), ensuring precision for thin-film device integration or coating studies.

Customization Potential

The success of this research hinges on precise control over doping concentration (TMB flow) and the ability to handle non-standard substrates. 6CCVD’s custom capabilities directly address these needs:

Custom Doping Recipes: 6CCVD’s in-house MPCVD expertise allows for precise control of boron incorporation, guaranteeing the metallic conductivity regime (Boron concentration > 10²⁰ cm^-3) required for high-conductivity applications like those demonstrated here.
Thickness and Dimension Control: While the paper focused on fibers, 6CCVD can supply large-area BDD plates/wafers up to 125 mm in diameter, suitable for scaling up BDD electrode manufacturing or for use as high-performance composite mold surfaces.
Advanced Polishing: The paper noted a reduction in roughness to 9 nm. 6CCVD offers standard polishing services for PCD down to Ra < 5 nm and SCD down to Ra < 1 nm, crucial for high-resolution C-AFM/sMIM studies or device fabrication.
Metalization Services: Although not the primary focus of this paper, 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for researchers requiring integrated contacts or patterned electrodes on BDD substrates for electrochemical or sensor applications.

Engineering Support

The complexity of achieving uniform, heavily doped diamond coatings requires expert consultation.

In-House PhD Team: 6CCVD maintains an expert team of PhD material scientists specializing in MPCVD diamond growth and characterization (Raman, electrical, structural).
Application Focus: We offer consultation on material selection and process optimization for similar high-performance conductive projects, including advanced composite interfaces, electrochemical sensors, and high-power electronics.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive diamond materials, supporting international research collaborations.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.apsusc.2023.156382

References

2013 - Advanced composite materials of the future in aerospace industry [Crossref]
2017 - A review on utilization of textile composites in transportation towards sustainability [Crossref]
2013 - The Application of Carbon Fiber Materials in Sports Equipment [Crossref]
2019 - Multifunctional application of carbon fiber reinforced polymer composites: Electrical properties of the reinforcing carbon fibers - A short review [Crossref]
2008 - A Study of Electrical Conductivity Improvement of Carbon-Fiber Reinforced Plastics by Conductive Nano-Particles Coating
2014 - Surface Treatment of Carbon Fibers - A Review [Crossref]
2014 - Carbon fiber surfaces and composite interphases [Crossref]
2015 - Improving the through-thickness thermal and electrical conductivity of carbon fibre/epoxy laminates by exploiting synergy between graphene and silver nano-inclusions [Crossref]
2018 - Through-thickness thermal conductivity enhancement and tensile response of carbon fiber-reinforced polymer composites [Crossref]