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

Abstract

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 C 2 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 C 2 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 C 2 in the boundary layer just above the substrate. These relations agree with theoretical models describing their importance in ͑flame͒ 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.

Two-dimensional simulation of an oxy-acetylene torch diamond reactor with a detailed gas-phase and surface mechanism

“…At this value of d, however, the increase in concentration behind the flame front is evident in neither the simulations nor the measurements. From 2D LIF pictures, 35 and in particular from their color reproductions in Ref. 38, however, it is clear that the maximum atomic hydrogen concentration lies some distance away from the flame front, in agreement with our simulations.…”

“…4, the simulated axial atomic hydrogen profile is compared to the profile measured with LIF. 35 The concentration predicted by 1D stagnation flow simulations is also depicted. At this flame-tip-to-substrate distance, the 2D profile matches the measured profile well, despite the large temperature gradients between the flame-tip and the substrate.…”

“…All these predictions are in agreement with experimental observations. 19,35 When comparing measured and predicted axial ͑Fig. 9͒ and radial ͑Fig.…”

“…To validate the oxy-acetylene flame simulations, radial and axial concentration profiles were compared to concentration profiles measured by Klein-Douwel et al 19,35 with the aid of LIF. In LIF, a laser sheet of light of a certain wavelength is directed through the flame.…”

Influence of nitrogen on diamond growth in oxyacetylene combustion chemical vapor deposition

“…13, which we have subsequently combined with a two-dimensional hydrodynamic model for laminar oxyacetylene flames. 14 These models were validated against experimental data [15][16][17][18] on growth rates and concentration profiles of gas phase intermediates C, CH, and H, as a function of flame-tip-to-substrate distance and substrate temperature. Our combined chemistry and hydrodynamic models were found to provide valuable insights in various important underlying mechanisms of oxyacetylene combustion CVD of diamond.…”