Optical Emission Spectroscopy study of resonant vibrational excitation of precursor molecules in the CO₂ laser-assisted flame deposition of diamond

Diamond thin films were deposited using C₂H₄/C ₂H₂/O₂ and C₃H₆/O ₂ combustion flames. At points where the diamond films were being deposited, Optical Emission Spectroscopy (OES) measurements showed that excited C₂ and CH species appear abundantly. The relative emission intensity of these species depended on the precursors used to generate the combustion flames. In addition, the irradiation of C₂H₄/C ₂H₂/O₂ and C₃H₆/O ₂ flames by a continuous-wave CO₂ laser beam (10.591 μm) resulted in increased optical emission intensity from the excited species due to resonant absorption of laser energy. OES was used to obtain molecular spectra of the excited C₂ and CH species in the flames for different gas combinations and laser powers. The overall intensity of C₂ and CH species were calculated from these spectra. The Boltzmann equation was used to obtain rotational temperatures from the spectra of the excited species. The results were used to understand the mechanism of the vibrational excitation and to study the effect of laser irradiation on flame temperature. For each condition, the intensity ratios and temperatures obtained using OES were correlated with the diamond films deposited on cemented tungsten carbide (WC-Co) substrates.