Enhancement of short/medium-range order and thermal conductivity in ultrahard sp3 amorphous carbon by C70 precursor

At a Glance

Metadata	Details
Publication Date	2023-11-29
Journal	Nature Communications
Authors	Yuchen Shang, Mingguang Yao, Zhaodong Liu, Rong Fu, Longbiao Yan
Institutions	Dalian University of Technology, Shanghai Institute of Applied Physics
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultrahard sp³ Amorphous Carbon

6CCVD Material Science Analysis (Reference: Nature Communications, 2023, 14:7860)

This document analyzes the synthesis and properties of ultrahard sp³ amorphous carbon (a-C) derived from C₇₀ precursors under High Pressure High Temperature (HPHT). While the research focuses on amorphous materials, the achieved properties—specifically extreme hardness and thermal conductivity—directly relate to the core performance metrics of 6CCVD’s Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) products.

Executive Summary

Novel Material Synthesis: Highly transparent, nearly pure sp³-hybridized bulk amorphous carbon (AC70-1) was successfully synthesized using C₇₀ fullerene precursors under 30 GPa and 1100 °C.
Record Thermal Performance: The material achieved a thermal conductivity (κ) of 36.3 ± 2.2 W m^-1 K^-1, establishing a new record for any known amorphous solid.
Ultrahard Mechanical Properties: AC70-1 exhibited exceptional mechanical strength with a Vickers hardness (H_V) of 109.8 ± 5.6 GPa, surpassing similar amorphous carbon synthesized from C₆₀.
High Purity: EELS analysis confirmed an extremely high sp³ content of 96.2 ± 0.9%, indicating near-complete transformation from the fullerene structure.
Microstructural Control: Enhanced properties are linked to the C₇₀ precursor’s topology, which promotes stronger short/medium-range structural order (SRO/MRO) and a higher fraction of hexagonal-diamond-like clusters.
Strategic Implication: The work provides a validated strategy for modifying the microstructure of amorphous solids by tuning the precursor’s concentration of carbon pentagons and hexagons.

Technical Specifications

Parameter	Value	Unit	Context
Synthesis Pressure (P)	30	GPa	HPHT condition for optimal AC70-1
Synthesis Temperature (T)	1100	°C	HPHT condition for optimal AC70-1
sp³ Hybridization Content	96.2 ± 0.9	%	Quantified by EELS (Highest purity achieved)
Vickers Hardness (H_V)	109.8 ± 5.6	GPa	Measured at 9.8 N load (Ultrahard classification)
Thermal Conductivity (κ)	36.3 ± 2.2	W m^-1 K^-1	Record high for an amorphous material
Optical Bandgap (E_g)	2.80	eV	Largest bandgap observed in the series
Average Density (ρ)	3.4 ± 0.1	g/cm³	Determined by simple floating method
C-C-C Bond Angle	108.8	°	Close to ideal tetrahedral angle (109.5°)
Nearest Neighbor Distance (r₁)	1.55	Å	Short-range atomic configuration
Local Ordered Region Fraction	38.1 ± 3.8	%	Total areal fraction of diamond-like MRO clusters in AC70-1

Key Methodologies

The synthesis and characterization of the sp³ amorphous carbon utilized extreme conditions and advanced analytical techniques:

HPHT Synthesis: C₇₀ powders were compressed in a 10-MN Walker-type large-volume press using a 7/3 cell assembly (octahedral edge length/truncated edge length of anvil).
Temperature Control: Temperature was measured using W₇₅Re₂₅-W₉₇Re₃ thermocouples adjacent to the sample capsule (Rhenium capsule acting as heater).
Processing Profile: Samples were compressed slowly (10 hours) at room temperature, heated at 100 °C min^-1, held for 1-2 hours, and then quenched rapidly (~500 °C s^-1).
Structural Analysis (XRD): X-ray diffraction (Cu Kα radiation) confirmed the amorphous structure via two very broad diffraction peaks (42° and 84°).
Bonding State Analysis (EELS): Carbon K-edge Electron Energy Loss Spectroscopy was used to quantify the sp³ content by calculating the ratio of integrated areas under the 1s-π* (sp²) and 1s-σ* (sp³) peaks.
Microstructure Imaging (HRTEM/SAED): High-Resolution Transmission Electron Microscopy and Selected Area Electron Diffraction confirmed the maze-like amorphous pattern and the presence of diamond-like Medium-Range Order (MRO) clusters.
Thermal Transport Measurement (TDTR): Time-Domain Thermoreflectance, a noncontact pump-probe technique, was employed to measure the thermal conductivity (κ) of the recovered samples after Al transducer film deposition.

6CCVD Solutions & Capabilities

This research highlights the critical role of high sp³ content and structural order in achieving extreme mechanical and thermal properties in carbon materials. While the paper focuses on HPHT amorphous carbon, 6CCVD specializes in MPCVD crystalline diamond, which serves as the industry benchmark for these exact performance metrics.

6CCVD offers materials and services essential for replicating, benchmarking, and extending this type of high-performance carbon research:

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Rationale & Performance
Extreme Thermal Management (κ = 36.3 W m^-1 K^-1)	High Purity Thermal Grade SCD	SCD offers thermal conductivity > 2000 W m^-1 K^-1, far exceeding the amorphous limit, ideal for heat spreading and high-power electronics.
Ultrahard Mechanical Testing (H_V = 109.8 GPa)	Optical Grade SCD	Provides the highest structural perfection and hardness benchmark. Available with ultra-smooth polishing (Ra < 1nm) for friction and wear studies.
Large-Area Substrates for HPHT	Polycrystalline Diamond (PCD)	PCD wafers (up to 125mm diameter) and substrates (up to 10mm thickness) offer robust, high-purity platforms necessary for large-volume HPHT cell assemblies and subsequent material recovery.
Tunable Electronic/Optical Properties	Boron-Doped Diamond (BDD)	For research requiring tunable bandgaps or high electrochemical stability, 6CCVD BDD provides precise doping control for semiconductor and electrochemistry applications.

Customization Potential

The complexity of synthesizing and characterizing novel carbon allotropes demands highly tailored material solutions. 6CCVD provides comprehensive engineering services:

Custom Dimensions: We offer plates and wafers up to 125mm (PCD) and custom laser cutting services to meet the precise geometric requirements of HPHT cell assemblies or advanced characterization setups (e.g., millimeter-sized samples used in this study).
Advanced Polishing: For optical and mechanical testing (like the Vickers hardness and UV-visible absorption measurements performed), 6CCVD guarantees superior surface quality, achieving Ra < 1nm on SCD and Ra < 5nm on inch-size PCD.
Metalization Services: The TDTR thermal measurement technique used in the paper requires thin metal transducer films. 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) to ensure optimal film quality, adhesion, and thermal coupling for accurate thermal transport studies.

Engineering Support

6CCVD’s in-house PhD team specializes in the structure-property relationships of CVD diamond. We can assist researchers and engineers with material selection and optimization for similar Ultrahard Carbon Allotrope projects, ensuring the chosen diamond substrate or film provides the necessary purity, thermal stability, and mechanical integrity.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-023-42195-5