THERMOCHEMICAL KINETICS OF A PROPOSED MECHANISM FOR DIAMOND GROWTH FROM ACETYLENE

We have performed a thermochemical and kinetic analysis of a previously proposed mechanism for diamond growth from C2H2. We estimate enthalpy and entropy changes for each step in the mechanism using the MM3 molecular mechanics code. Rate constants are estimated based on the assumption that reaction cross sections measured for analogous gas phase reactions may be applied to gas-surface reactions. Gas phase species concentrations are taken from measurements and modeling. The rate equations are then integrated. According to the analysis, each step in the proposed mechanism is exothermic (DELTA-H < 0), but the reduction in entropy is so great that this mechanism does not produce diamond at a significant rate. This result does not rule out the possibility of growth from C2H2 by some different reaction mechanism.