Chemical vapor deposition of diamond in flames and fluidized beds

An experimental and computational study of chemical vapor deposition (CVD) of diamond in low pressure flames, and an experimental study of microwave plasma-enhanced CVD of diamond on particles in fluidized beds are presented. Diamond film growth experiments were performed in low pressure (30-52 Torr) acetylene/oxygen flames and the effects of varying substrate temperature, equivalence ratio, and pressure on diamond growth were examined. Uniform diamond films fully covering 5 cm diameter substrates at growth rates of up to 2.3 {dollar}mu{dollar}m/hr were grown at 30 Torr using a 4 cm diameter flat flame burner.; To extend the combustion synthesis technique for diamond to fuels other than acetylene, growth experiments using several alternative hydrocarbon fuels (MAPP, propylene, ethylene, and propane) were performed at 50-180 Torr. Well-faceted diamond films at growth rates of up to 1.0 {dollar}mu{dollar}m/hr were grown in these alternative fuel flames. An economic comparison study showed that switching from acetylene to propylene may be able to lower the fuel cost per unit mass of diamond by roughly a factor of three.; The model predicts peak flame temperatures above the adiabatic flame temperature, and a chemical environment near the substrate far from its equilibrium state. The simulations of low pressure (25-30 Torr) acetylene/oxygen flames near diamond growth conditions suggest that increasing the mass flow rate while reducing the pressure is favorable for increasing the growth rate.; Although slightly lower than for acetylene/oxygen flames, alternative fuel flames are predicted to have high enough H and CH{dollar}sb3{dollar} concentrations at the substrate to grow diamond at a reasonable growth rate. The results indicate that nonequilibrium flame chemistry is important in the low pressure combustion environment.; To grow continuous, conformal diamond coatings on small, irregular objects, experiments were performed using microwave plasma-enhanced fluidized beds. Studies were carried out to map the parameter space leading to diamond growth, and the effects of varying gas composition and pressure on deposited carbon morphology, growth rate, and nucleation density were examined.; Oxygen addition had a strong influence on growth rate and morphology over the range of gas compositions studied. Well-faceted diamond at a growth rate of up to 6 {dollar}mu{dollar}m/hr was observed to grow on 0.25-0.7 mm diameter silicon and SiO{dollar}sb2{dollar} seed particles using up to 15.0% CH{dollar}sb4{dollar} in H{dollar}sb2{dollar} with addition of O{dollar}sb2{dollar}. No surface pretreatment was necessary for diamond nucleation. Well-faceted continuous diamond coatings were deposited on seed particles after 8 hours at 9 Torr and 120 Watts of microwave power with flow rates of 160 sccm of 2.0% CH{dollar}sb4{dollar} in H{dollar}sb2{dollar} and 3 sccm of O{dollar}sb2{dollar}. These results show that plasma-enhanced fluidized beds can be effectively used to deposit diamond coatings on small objects of complex shape.