Spatial distributions of H, CN, and C2 in a diamond-growing oxyacetylene flame

Two-dimensional laser-induced fluorescence (2D-LIF) measurements are applied to the chemical vapor deposition (CVD) of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen, C₂, and CN in the gas phase during diamond growth. Experiments are carried out in laminar flames and reveal that atomic hydrogen is ubiquitous at and beyond the flame front. Its presence extends to well outside the diamond deposition region, whereas the C₂ distribution is limited to the flame front and the acetylene feather. CN is found to be present mostly at the outer edge of the flame, where ambient air interacts with flame gases. The diamond layers obtained are characterized by optical as well as scanning electron microscopy (SEM) and cathodoluminescence topography (CL). Clear relations are observed between the local variations in growth rate of the diamond layer and the distribution of H, C₂, and CN in the boundary layer just above the substrate. Further relations between CN and the morphology and the nitrogen incorporation as identified by CL of the deposited diamond layer are found as well. These relations agree with theoretical models describing the importance of the mentioned species in (flame) deposition processes of diamond. Three separate regions can be discerned in the flame and the diamond layer, where the gas phase and diamond growth are predominantly governed by the flame source gases, the ambient atmosphere, and the interaction of both, respectively.