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

Rate coefficients, event probabilities, and desorption probabilities a t 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 a nd for H on sp(2) carbon and H on sp(3) carbon are computed using clas sical trajectory methods on the empirical hydrocarbon no 1. potential developed by Brenner. The results show that the chemisorption rates fo r nonradical species such as C2H2 and C2H4 are 2 or more orders of mag nitude smaller than the values obtained for radicals. For ethylene, th e 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 t o the lattice. If only one bond forms, 97% of the acetylene desorbs wi thin four C-C vibrational periods. All of the radical species have che misorption rates in the range of 10(12)-10(13) cm(3)/(mol s). The leas t reactive of the radical species investigated is CH3. However, its hi gh concentration in most chemical vapor deposition experiments makes i t an important growth species. The chemisorption rates for C-n (n = 1, 2, 3) are a monotonically decreasing function of n. The associated de sorption probabilities increase as n increases. Atomic carbon has the largest chemisorption rate of all of the species investigated. Consequ ently, it is likely to be an important growth species in plasma experi ments where its concentration is sufficiently high. Hydrogen atom addi tion to sp(2) and sp(3) carbon is found to be very fast with rate coef ficients 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 atom s had to be extracted from sp(2) carbon to propagate diamond-film grow th.