Spatial distributions of atomic hydrogen and C2 in an oxyacetylene flame in relation to diamond growth

Two-dimensional laser induced fluorescence measurements are applied to the chemical vapour deposition of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen and C2 in the gas phase during diamond growth. Experiments are carried out in both laminar and turbulent 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. The diamond layers obtained are characterized by optical as well as scanning electron microscopy and Raman spectroscopy. Clear relations are observed between the local variations in growth rate and quality of the diamond layer and the distribution of H and C2 in the boundary layer just above the substrate. These relations agree with theoretical models describing their importance 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.