GROWTH OF DIAMOND FILMS USING AN ENCLOSED METHYL-ACETYLENE AND PROPADIENE COMBUSTION-FLAME

Diamond growth in low-pressure combustion flames was studied using a s afer, more economical substitute for acetylene: a mixture of methylace tylene, propadiene, and liquefied petroleum (MAPP gas). A burner-stabi lized, low pressure, flat, premixed flame was used to deposit continuo us, uniform thickness diamond films on a heated molybdenum substrate. This work identities the dependence of film growth rate and quality on the fuel-to-oxygen ratio and the burner-substrate separation distance at two different reactor pressures of 70 and 250 Torr. A single subst rate temperature of 800 degrees C was used to consistently produce wel l-faceted films. For the MAPP/O-2, premixed flame, it was determined t hat the optimal fuel-to-oxygen ratios for diamond growth are 0.53 at 7 0 Torr and 0.51 at 250 Torr. Typical growth rates at these conditions were on the order of 1 mu m h(-1). However, growth rate and quality ar e very sensitive to the fuel-to-oxygen ratio, falling off rapidly in e ither direction from the optimal value. Increasing the ratio enhances secondary nucleation, and eventually results in graphitic and amorphou s material. The growth rate is also very sensitive to the burner-subst rate separation distance due to tight coupling between the transport a nd chemical kinetic time scales in the combustion reactor. (C) 1998 Pu blished by Elsevier Science S.A. All rights reserved.