THEORETICAL-STUDIES OF ELEMENTARY CHEMISORPTION REACTIONS ON AN ACTIVATED DIAMOND LEDGE SURFACE

Rate coefficients, event probabilities, and desorption probabilities at 1250 K for chemisorption reactions of C2H2, C2H, CH3, CH2 C2H4, C2H3, C3H, and C-n (n = 1, 2, 3) on an activated diamond ledge structure and for H on sp(2) carbon and H on sp(3) carbon are computed using classical trajectory methods on the empirical hydrocarbon no 1. potential developed by Brenner. The results show that the chemisorption rates for nonradical species such as C2H2 and C2H4 are 2 or more orders of magnitude smaller than the values obtained for radicals. For ethylene, the chemisorption rate is on the order of 10(6) cm(3)/(mol s), 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 10(11) cm(3)/(mol s) provided acetylene can form two C-s-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 of 10(12)-10(13) cm(3)/(mol s). The least reactive of the radical species investigated is CH3. However, its high concentration in most chemical vapor deposition experiments makes it an important growth species. The chemisorption rates for C-n (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 sp(2) and sp(3) carbon is found to be very fast with rate coefficients of 1.6 x 10(13) and 3.7 X 10(13) cm(3)/(mol s), respectively. This finding removes the bottleneck that would exist if hydrogen atoms had to be extracted from sp(2) carbon to propagate diamond-film growth.