Martin D. Perry and Lionel M. Raff
J. Phys. Chem. 98, 4375 (1994)
Abstract
Rate coefficients, event probabilities, and desorption probabilities at 1250 K for chemisorption reactions of C2H2, C2H, CH3, CH2, C2H4, C2H3, C3H, and Cn (n = 1, 2, 3) on an activated diamond-ledge structure and for H on sp2 carbon, and H on sp3 carbon are computed using classical trajectory methods on the empirical hydrocarbon #1 potential developed by Brenner. The results show that the chemisorption rates for nonradical species such as C2H2 and C2H4 are two or more orders of magnitude smaller than the values obtained for radicals. For ethylene, the chemisorption rate is on the order of 106 cm3/mole-sec, which is too small to permit C2H4 chemisorption to play a role in diamond-film formation. The chemisorption rate for acetylene lies in the range 1-2 x 1011 cm3/mole-sec provided acetylene can form two Cs-C bonds to the lattice. If only one bond forms, 97 % of the acetylene desorbs within four C-C vibrational periods. All of the radical species have chemisorption rates in the range 1012 - 1013 cm3/mole-sec. The least reactive of the radical species investigated is CH3. However, its high concentration in most CVD experiments makes it an important growth species. The chemisorption rates for Cn (n = 1,2,3) are a monotonically decreasing function of n. The associated desorption probabilities increase as n increases. Atomic carbon has the largest chemisorption rate of all of the species investigated. Consequently, it is likely to be an important growth species in plasma experiments where its concentration is sufficiently high. Hydrogen-atom addition to sp2 and sp3 carbon is found to be very fast with rate coefficients of 1.6 x 1013 and 3.7 x 1013 cm3/mole-sec, respectively. This finding removes the bottleneck that would exist if hydrogen atoms had to be extracted from sp2 carbon to propagate diamond-film growth.