The influence of differences in gas phase between turbulent and laminar acetylene-oxygen combustion flames on diamond growth

Abstract

This study describes the deposition of polycrystalline diamond layers on molybdenum substrates, using both laminar and turbulent acetylene-oxygen flames. The use of accurate temperature and flow control systems allowed for a good comparison between diamond layers obtained by a specially designed turbulent burner and a commercially available laminar burner. With constant oxygen flows and temperatures, the deposits obtained with both types of flame in general behave similarly as a function of the applied supersaturation and the position of the substrate in the acetylene feather. Usually continuous diamond layers formed by well-faceted connected crystallites were obtained in the central area of the deposits. These parts of the diamond layers are of good quality, as judged from Raman spectroscopy and their blue band A cathodoluminescence emission. Surprisingly the central area, as obtained by the turbulent flame, is somewhat smaller than from the laminar flame. This, as well as other local differences in growth rate, morphology and impurity incorporation of the deposits, is explained by a model involving the increased mixing rates in the turbulent flame compared with the laminar gas phase.