Nitrogen additions and resonant laser energy coupling on diamond deposition using combustion chemical vapor deposition

Lasers feature a potential to steer chemical reactions in combustion flames through resonant excitation of precursors, which changes the species ratio for material synthesis. In this study, diamond deposition using an O₂/C₂H₂/C₂H₄ flame with NH₃ additions was investigated under the CO₂ laser excitation of the wagging mode of the C₂H₄ molecules. The diamond crystallinity is restored and improved by the resonant laser irradiation. The diamond crystallinity is restored and improved by the resonant laser irradiation. Field-enhanced thermionic emission current was monitored to determine the diamond incubation time and the subsequent growth. Optical emission spectroscopy (OES) was employed to investigate the emission intensity ratio between CN and CH species in the activation zone. It was found that the emission intensity ratio of I(CN)/I(CH) increases with the NH₃ addition given a fixed laser power density, while the ratio decreases with the augment of laser power density at a fixed NH₃ concentration. A correlation between I(CN)/I(CH) ratio and diamond deposition was established. Large areas of well-faceted and high-phase-purity diamond film could be formed within a short incubation time at a low I(CN)/I(CH) ratio. On the contrary, a high I(CN)/I(CH) ratio results in long incubation time (if diamond nucleates) and deteriorated diamond films. The innovation of this study lies in demonstrating the capability of laser resonance excitation modulation reaction pathways and providing crucial insights into nitrogen addition and resonance laser energy coupling in diamond deposition using combustion chemical vapor deposition.