THEORETICAL-STUDIES OF ELEMENTARY CHEMISORPTION REACTIONS ON AN ACTIVATED DIAMOND(111) TERRACE

Rate coefficients, event probabilities, and dissociation probabilities for chemisorption reactions of C2H2, C2H, CH3, CH2, C2H4, C2H3, C3H, and C-n (n = 1-3) on an activated diamond (111) terrace structure and for H on sp(3) carbon are computed using classical trajectory methods on the empirical hydrocarbon no. 1 potential developed by Brenner. The rate coefficients for nonradical species are between a factor of 2 to an order of magnitude smaller than the values obtained for radicals. The ethylene coefficient on a terrace is sufficiently large to permit C2H4 to compete with C2H2 as a growth species. However, the C2H4 dissociation probability is 7 times that for C2H2. Acetylene is found to chemisorb more readily an a terrace than on a ledge structure. All of the radical species investigated have chemisorption rate coefficients in the range 10(11)-10(12) cm(3)/mol s. The least reactive species is CH3. Atomic carbon has the largest chemisorption rate coefficient of all of the species investigated. This has also been found to be the case for chemisorption on a ledge structure. Consequently, atomic carbon should be a major growth species in plasma-CVD experiments where its concentration is expected to be large. Hydrogen atom addition to sp(3) carbon is found to be very fast. Chemisorption rates on a terrace are found to be slower than on a ledge structure for all hydrocarbon species except C3H. These results are consistent with previously reported thermodynamic Monte Carlo simulations reported by Xing and Scott and with recent experimental observations made by Li et al. and by Komanduri and co-workers. Examination of the present radical rate coefficients along with those previously obtained for a ledge structure shows that there is an approximate linear correlation between the rate coefficients and the number of atoms present in the radical. The extent of this correlation is significantly greater for chemisorption at a ledge than on a terrace. For radicals containing an equal number of atoms, the one with the fewest number of hydrogen atoms usually exhibits the larger chemisorption rate coefficient.