Laser-assisted synthesis of diamond crystals in open air through vibrational excitation of precursor molecules

Abstract

Fast growth of diamond crystals in open air was achieved by laser-assisted combustion synthesis through vibrational excitation of precursor molecules. A wavelength-tunable CO₂ laser (spectrum range from 9.2 to 10.9 μm) was used for the vibrational excitation in synthesis of diamond crystals. A pre-mixed C₂H₄/C₂H₂/O₂ gas mixture was used as precursors. Through resonant excitation of the CH2-wagging mode of ethylene (C2H4) molecules using the CO2 laser tuned at 10.532 Μm, high-quality diamond crystals were grown on silicon substrates with a high growth rate of ~139 μm/hr. Diamond crystals with a length up to 5 mm and a diameter of 1 mm were grown in 36 hours. Sharp Raman peaks at 1332 cm^-1 with full width at half maximum (FWHM) values around 4.5 cm^-1 and distinct X-ray diffraction spectra demonstrated the high quality of the diamond crystals. The effects of the resonant excitation of precursor molecules by the CO2 laser were investigated using optical emission spectroscopy.