Diamond film synthesis in low-pressure premixed methane-oxygen flames

Abstract

We present the successful demonstration of diamond film synthesis in low-pressure premixed methane-oxygen flames. Experiments are performed in a low-pressure flat-flame facility that has been employed previously to study diamond synthesis in premixed acetylene-oxygen and ethylene-oxygen flames. The quality of the diamond films deposited is comparable to that deposited using these other flames, and the growth rate is approximately 0.2–0.3 μm/h; some factor of 10 less than acetylene-oxygen flames and one-third of that obtained for ethylene-oxygen flames. However, carbon conversion efficiencies are remarkably similar, since the cold gas velocities used here are substantially less, because of the lower burning velocities. The equivalence ratios employed in these methane-oxygen flames are in the 1.8–2.0 range. These values correspond to C:O ratios that are substantially lower than those that have been used to grow good quality diamond in acetylene-oxygen and ethylene-oxygen flames at low and atmospheric pressure. General observations suggest that the quality is only slightly sensitive to changes in equivalence ratios and very sensitive to substrate temperature. Uniform diamond films over areas of about 5.5 cm2 are deposited with substrate temperatures of approximately 900 °C.