Competing surface oxidation reactions during diamond synthesis in low pressure flames

Carbon oxidation reactions affecting diamond growth in low pressure premixe d flames are addressed. Modifications are made to the relatively simple yet robust Harris growth mechanism [S. J. Harris: Appl. Phys. Lett. 56 (1990) 2298], to better capture anomalous behavior seen in past experimental studi es of films deposited from low pressure acetylene-oxygen (C2H2-O-2), ethyle ne-oxygen (C2H4-O-2), and methane-oxygen (CH4-O-2) flames. With surface rea ctions involving oxygen, detailed simulations are shown to better predict t he observed growth rates; generally to within a factor of two for C2H2-O-2 and C2H4-O-2 flames. More importantly, the simulations with oxidation react ions capture the sharp onset of growth as reactant mixture compositions are varied towards rich flame conditions. The model is less successful at capt uring the growth rates seen in CH4O2 flames. The diamond synthesized in CH4 -O-2 is seen to be more defective, with a seemingly greater fraction of sp( 2) bonds, the presence of which are not accounted for in the simple growth mechanism employed in this study.