The Microzone Structure Regulation of Diamond/Cu-B Composites for High Thermal Conductivity - Combining Experiments and First-Principles Calculations

At a Glance

Metadata	Details
Publication Date	2023-02-28
Journal	Materials
Authors	Zhongnan Xie, Wei Xiao, Hong Guo, Boyu Xue, Hui Yang
Institutions	State Key Laboratory of Nonferrous Metals and Processes, General Research Institute for Nonferrous Metals (China)
Citations	9
Analysis	Full AI Review Included

Executive Summary

High Performance Achieved: Diamond/Cu composites alloyed with Boron (B) achieved a maximum thermal conductivity (TC) of 694 W/(mK) at an optimal B content of 0.5 wt.%. This represents a 2.5-fold increase over the baseline diamond/Cu composite (261 W/(mK)).
Interfacial Carbide Formation: Boron atoms diffuse toward the diamond/Cu interface (diffusion barrier 0.87 eV) and are highly favorable to segregate (segregation energy -1.10 eV), leading to the exothermic formation of a B₄C carbide interlayer.
Phonon Transmission Bridge: First-principles calculations confirm that the B₄C interlayer acts as a crucial phonon transmission bridge. Its phonon spectrum (5-34 THz) effectively overlaps the low-frequency Cu spectrum (0-8 THz) and the high-frequency diamond spectrum (10-40 THz).
Microzone Structure Enhancement: HRTEM revealed that the B₄C layer forms a unique nano-cone or “dentate” structure extending from the diamond surface, which further enhances the efficiency of phononic transport across the interface.
Heat Transfer Mechanism: The enhancement in TC is primarily attributed to improved phononic transport via the B₄C bridge and dentate structure, as the electronic contribution to heat transfer across the interface was calculated to be relatively insignificant (1.13 G₀/nm²).
Process Optimization: Increasing the Boron content beyond 0.5 wt.% (e.g., 1.0 wt.%) leads to thicker B₄C layers, which subsequently increases interfacial thermal resistance and reduces the overall composite TC (down to 647 W/(mK)).

Technical Specifications

Parameter	Value	Unit	Context
Maximum Thermal Conductivity (K)	694	W/(mK)	Diamond/Cu-0.5 wt.%B composite
Baseline Thermal Conductivity (K)	261	W/(mK)	Diamond/Cu composite (0 wt.%B)
Optimal Boron Content	0.5	wt.%	Alloyed into Cu matrix
Diamond Content	60	vol.%	Reinforcing phase content
Infiltration Temperature	1250	°C	Vacuum Pressure Infiltration (VPI)
Diamond Grain Size	100	µm	Single-crystal diamond filler
Boron Diffusion Energy Barrier	0.87	eV	Migration path between OISs in bulk Cu
Boron Segregation Energy (E_seg)	-1.10	eV	Favorable segregation to the diamond/Cu interface
B₄C Formation Enthalpy (E_f)	-1.36	eV/atom	Exothermic reaction (B + C → B₄C)
B₄C Phonon Frequency Range	5 to 34	THz	Phonon transmission bridge
Copper Phonon Frequency Range	0 to 8	THz	Bulk Cu
Diamond Phonon Frequency Range	10 to 40	THz	Bulk diamond
Diamond/Cu Interface Conductance (Electronic)	1.13 G₀/nm²	G₀/nm²	Calculated electronic contribution (relatively low)
Cu Metal Conductance (Electronic)	13.63 G₀/nm²	G₀/nm²	Reference pure Cu metal
Lattice Mismatch (Calculated)	1.65	%	Cu(111)/Diamond(111) interface model

Key Methodologies

Composite Preparation: Diamond/Cu-B composites were fabricated using Vacuum Pressure Infiltration (VPI). Diamond preforms were infiltrated with Cu-B alloys (0, 0.5, and 1.0 wt.% B) at 1250 °C.
Microstructure Characterization: Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to analyze fracture surfaces and the nano-scale structure of the diamond-B₄C-Cu interface.
Phase Identification: X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) confirmed the presence of the newly formed B₄C phase near the diamond interface.
Thermal Measurement: Thermal diffusivity (α) was measured using a thermal conductivity tester (LFA447). Thermal conductivity (K) was calculated using the formula K = α·ρ_pc·C_p.
First-Principles DFT Calculations (VASP): Density Functional Theory (DFT) was employed to determine the stability of Boron occupation sites in Cu, calculate the Boron diffusion energy barrier (using the Nudged Elastic Band, NEB, method), and analyze segregation energies.
Electronic Transport Modeling: The transmission coefficients and electrical conductance were calculated using the Nanodcal software package within the Non-Equilibrium Green’s Function-DFT (NEGF-DFT) framework.
Phonon Analysis: Phonon Density of States (PDOS) for bulk materials (Diamond, Cu, B₄C) and solid solutions (Cu₄B) were obtained using the Cambridge Serial Total Energy Package (CASTEP) to model phononic coupling efficiency.

Commercial Applications

High-Density Integrated Circuits (ICs): Used as advanced heat spreaders and heat sinks for microprocessors and high-performance computing (HPC) chips, addressing the bottleneck of increasing power density.
Power Electronics Modules: Thermal substrates for high-power semiconductor devices (e.g., IGBTs, MOSFETs) in electric vehicles (EVs) and renewable energy systems, where efficient cooling is essential for reliability.
Radio Frequency (RF) and Microwave Devices: Substrates for high-power GaN and GaAs amplifiers used in 5G infrastructure and radar systems, leveraging the high TC to maintain junction temperature stability.
Laser and Optoelectronics: Thermal management components for high-power laser diodes and LED arrays, preventing thermal degradation and maintaining light output efficiency.
Aerospace and Defense Systems: Applications requiring lightweight, high-stiffness, and high-thermal-conductivity materials for reliable operation in extreme environments.

View Original Abstract

The interface microzone characteristics determine the thermophysical properties of diamond/Cu composites, while the mechanisms of interface formation and heat transport still need to be revealed. Here, diamond/Cu-B composites with different boron content were prepared by vacuum pressure infiltration. Diamond/Cu-B composites up to 694 W/(mK) were obtained. The interfacial carbides formation process and the enhancement mechanisms of interfacial heat conduction in diamond/Cu-B composites were studied by HRTEM and first-principles calculations. It is demonstrated that boron can diffuse toward the interface region with an energy barrier of 0.87 eV, and these elements are energetically favorable to form the B4C phase. The calculation of the phonon spectrum proves that the B4C phonon spectrum is distributed in the range of the copper and diamond phonon spectrum. The overlapping of phonon spectra and the dentate structure together enhance the interface phononic transport efficiency, thereby improving the interface thermal conductance.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma16052021

References

2018 - Effect of Ti interlayer on interfacial thermal conductance between Cu and diamond [Crossref]
2019 - Tailoring interface structure and enhancing thermal conductivity of Cu/diamond composites by alloying boron to the Cu matrix [Crossref]
2017 - Design of interfacial Cr3C2 carbide layer via optimization of sintering parameters used to fabricate copper/diamond composites for thermal management applications [Crossref]
2020 - High thermal conductivity and strong interface bonding of a hot-forged Cu/Ti-coated-diamond composite [Crossref]
2012 - High thermal conductivity composite of diamond particles with tungsten coating in a copper matrix for heat sink application [Crossref]
2013 - Microstructure and thermal conductivity of Cu-B/diamond composites [Crossref]
2019 - Graphene interlayer for enhanced interface thermal conductance in metal matrix composites: An approach beyond surface metallization and matrix alloying [Crossref]
2021 - Unveiling the interface characteristics and their influence on the heat transfer behavior of hot-forged Cu-Cr/Diamond composites [Crossref]