Possible behavior of a diamond (111) surface in methane/hydrogen systems

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Abstract
A combined numerical and experimental investigation into the behavior of diamond (111) surfaces in plasma CVD reactors is presented. Numerically, semiempirical molecular orbital methods are used as a model of diamond (111) surfaces represented by a 20-atom carbon cluster plus surface species. The abstraction of hydrogen atoms by gas-phase hydrogen atoms, the coverage dependence of the heat of formation for submonolayers of CH3 and C2H groups coadsorbed with H, and the energy change for abstraction of H atoms from the surface by various radicals in the gas phase are examined. No barrier to abstraction is found, steric effects in achieving clusters of CH3 groups are large, and C2H and atomic oxygen are found to be the most energetically favored for removal of adsorbed H. Experimentally, relative concentrations of atomic H in the near-surface region as a function of added O2 mole fraction were measured. A weak dependence on O2 concentration is observed, but does not appear to be significant enough to account for observed changes in growth rate. This suggests that other radical species be investigated for their contribution to diamond film growth.