Possible gas-phase reactions of H₂CH₄/ tetramethylsilane in diamond/β-SiC nanocomposite film deposition: An ab-initio study

The Si-C bond breakings in tetramethylsilane (TMS) when interacting with H/H₂ and the successive H abstractions from SiH₄/CH ₄ in the gas mixture of H₂/CH₄/TMS were studied at the CCSD(T)/6-311+G**// MP2/6-31+G** level of theory. Their rate constants between 1500 and 2500 K were estimated using a conventional transition state theory. The results indicate that (i) it is mainly the H radical that causes the Si-C bond breaking in TMS, and (ii) the successive H abstractions from SiH₄ are much easier and faster than those from CH₄. At low temperatures the differences of rate constants among the four types of the reactions are large, but generally reduced at high temperatures. The reaction rates show no selectivity over the pressure as verified at P = 0.00025, 0.025, 1, and 100 atm, respectively. Our results could provide the following microscopic level understanding of reactions in the synthesis of diamond/β-SiC nanocomposite films. Although the Si content is smaller than that of C in the precursor gases, the gas mixture activated by microwave plasma technique could provide Si sources with a higher rate. The produced Si sources with excellent rigidity in sp³ hybridization competitively occupy the space on the substrate together with C sources, resulting in the deposition of diamond/β-SiC nanocomposite films. © 2007 American Chemical Society.