High-Pressure Laser Reactive Synthesis Within Diamond Anvil Cells of Carbon Allotropes from Methanol

At a Glance

Metadata	Details
Publication Date	2025-03-24
Journal	Crystals
Authors	Mohamad E. Alabdulkarim, James Maxwell
Institutions	La Trobe University
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Pressure Laser Reactive Synthesis of Carbon Allotropes

Executive Summary

This technical analysis reviews the successful synthesis of various carbon allotropes (diamond, CNTs, amorphous carbon) from methanol using Laser Reactive Synthesis within Diamond Anvil Cells (LRS-DAC). The findings highlight the potential for highly localized, selective material growth under extreme conditions, a key area where 6CCVD’s advanced MPCVD diamond materials provide critical enabling technology.

Core Achievement: Selective synthesis of single-crystal diamond (SCD), nanocrystalline diamond (NCD), microcrystalline diamond (MCD), and carbon nanotubes (CNTs) from methanol under pressures up to 15 GPa.
Methodology: LRS-DAC employed a tightly focused 1064 nm continuous-wave laser (20 µm beam waist) to induce localized decomposition and reaction.
Extreme Conditions: Experiments spanned pressures from 0.01 GPa (100 bar) to 15 GPa, significantly exceeding the critical point of methanol.
Material Quality: Synthesized diamond films exhibited structural defects and residual stresses, evidenced by a significant blue-shift (10-12 cm^-1) and high FWHM (4.8 cm^-1) of the diamond peak.
Catalytic Growth: Carbon nanotube growth was observed originating from the Inconel 718 gasket material, which acted as a catalyst in cooler regions of the DAC chamber.
Novel Discovery: The identification of previously unknown Raman signatures suggesting the formation of complex compounds containing carbon rings and modified O-H stretching vibrations under high-pressure, moderate-temperature (HPMT) conditions.

Technical Specifications

The following hard data points were extracted from the LRS-DAC experiments:

Parameter	Value	Unit	Context
Pressure Range Investigated	0.01 to 15	GPa	LRS-DAC experiments using methanol precursor
Maximum DAC Pressure Capability	20	GPa	Bragg-Mini DAC limit without damage
Synthesis Laser Wavelength	1064	nm	Continuous-Wave (cw) mode
Laser Beam Waist (1/e² focus)	20	µm	Achieved selective, localized synthesis
Incident Laser Power (Low)	9.0	W	Used for 0.01 GPa and 2.2 GPa experiments
Incident Laser Power (High)	14.6	W	Used for 4.0 GPa and 15 GPa experiments
Beam Intensity (at 14.6 W)	4647	kW/cm²	Calculated intensity at the diamond anvil
Diamond Peak Shift (Observed)	10-12	cm^-1	Blue-shifted from nominal 1332 cm^-1, indicating residual stress
Diamond Peak FWHM (Defected Film)	4.8	cm^-1	Significantly higher than high-quality SCD (1.5-3 cm^-1)
Hydrogen Content (MCD Powder)	30.8	%	Derived using Casiraghi’s method
Ruby Fluorescence Peak (Nominal)	694.29	nm	Used for real-time pressure monitoring

Key Methodologies

The LRS-DAC system enabled precise control over extreme pressure and localized temperature gradients:

High-Pressure Setup: A Bragg-Mini Diamond Anvil Cell (DAC) was used, featuring 0.50 mm cutlets. Inconel 718 gaskets were employed, creating a chamber approximately 300 µm in diameter.
Precursor and Seeding: Pure methanol (>99% purity) was used as the precursor. Fine graphite powder (<20 µm) was included to aid in seeding growth, and crushed ruby micro-particles were added for pressure calibration.
Pressure and Temperature Monitoring: Real-time pressure was monitored using ruby fluorescence excited by a 457 nm laser. The reaction zone heating was monitored in real-time at red and near-IR wavelengths.
Laser Reactive Synthesis (LRS-DAC): A 1064 nm continuous-wave laser was focused via a 40 mm focal length achromat to achieve a 20 µm beam waist, intentionally inducing chemical reactions within the high-pressure environment.
Microstructural Analysis: Synthesized allotropes were characterized using high-resolution Field Emission Scanning Electron Microscopy (FE-SEM) and Confocal Raman Spectroscopy (532 nm excitation, ~1 µm beam waist).

6CCVD Solutions & Capabilities

This research demonstrates the critical role of high-quality diamond in extreme synthesis environments and the need for precision materials in advanced carbon allotrope research. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond materials and customization services to replicate and advance this work.

Research Requirement/Challenge	6CCVD Solution & Capability	Technical Advantage
High-Pressure Optical Windows (DAC Anvils)	Optical Grade Single Crystal Diamond (SCD)	SCD substrates available up to 500 µm thick, offering superior mechanical strength, thermal conductivity, and optical transparency necessary for high-pressure (up to 20 GPa and beyond) and laser-heating applications.
Substrates for Film Synthesis	Electronic Grade SCD Wafers	SCD material with ultra-low defect density (Ra < 1 nm polished) for use as high-quality seed material, ensuring optimal conditions for epitaxial growth studies or minimizing background interference during Raman analysis.
Scaling Nanocrystalline/Microcrystalline Synthesis	Polycrystalline Diamond (PCD) Plates	Custom PCD plates available in large formats (up to 125 mm diameter) and thicknesses (up to 500 µm), enabling scale-up of NCD/MCD synthesis or use as robust, conductive substrates.
Controlling Catalytic Growth (CNTs)	Custom Metalization Services	Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu. Researchers can utilize 6CCVD’s metalization services to pre-pattern substrates with specific catalytic layers (e.g., Ni-Cr analogs) for controlled, localized CNT or diamond nucleation.
Precision Sample Preparation	Advanced Laser Cutting & Polishing	Custom dimensions and shapes are available via laser cutting. Precision polishing (Ra < 1 nm for SCD, Ra < 5 nm for PCD) ensures minimal surface scattering, critical for high-resolution confocal Raman and SEM analysis of synthesized microstructures.
Investigating Conductive Phases (BDD)	Boron-Doped Diamond (BDD)	6CCVD supplies BDD films and substrates, essential for future LRS-DAC experiments requiring conductive anvils or substrates to control localized heating or electrochemical reactions.

Engineering Support

The paper highlights the complexity of the C-H-O system under extreme conditions and the identification of unknown Raman signatures. 6CCVD’s in-house PhD team specializes in MPCVD diamond growth and material characterization. We offer expert consultation to assist researchers in optimizing material selection, interpreting complex spectral data, and designing custom substrates for similar High-Pressure Laser Reactive Synthesis projects.

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

View Original Abstract

This work targets a knowledge gap in the high-pressure decomposition of methanol, complementing prior moderate-pressure diamond anvil studies below 4 GPa and hyperbaric-pressure laser chemical vapour deposition (HP-LCVD) experiments below 0.01 GPa. Localised decomposition of methanol into various carbon allotropes was investigated at pressures of up to 15 GPa. Diamond anvil cell (DAC) pressures were monitored in real-time using ruby fluorescence and a high-resolution spectrometer. Selective saser reactive synthesis within diamond anvil cells (LRS-DAC) was achieved using a 20-micron 1/e2 laser beam focus—one order of magnitude smaller than the diamond anvil chamber dimensions. Confocal Raman spectroscopy and electron microscopy were employed to investigate the deposit’s local microstructure. Various carbon allotropes were synthesised selectively, including single-crystal diamond, nanocrystalline diamond, multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), and amorphous carbons. At least two unknown Raman signatures were observed and unlikely to be harmonics or combinations of ordinary Raman peaks, the closest known Raman spectra being that of catechol and polycatechol. Potential side reactions are proposed, where polymerisation and/or ring-formation may occur during high-pressure moderate-temperature (HPMT) conditions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst15040292

References

2009 - Diamond anvil cell, 50th birthday [Crossref]
2024 - Detection of thin film phase transformations at high-pressure and high-temperature in a diamond anvil cell [Crossref]
2025 - Disordering of graphene nanoplatelet, carbon nanotube and C60 fullerene under shear stress [Crossref]
2024 - A broadband pulse amplifier for Joule heating experiments in diamond anvil cells [Crossref]
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1998 - Direct transformation of graphite to cubic diamond observed in a laser-heated diamond anvil cell [Crossref]
2024 - In Situ Measurement Techniques Using Diamond Anvil Cell at High Pressure-Temperature Conditions: A Review [Crossref]