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

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.