First-principle study on reactions of diamond (100) surfaces with hydrogen and methyl radicals

Density-functional calculations have been performed to investigate the reaction of diamond (100) surfaces with the hydrogen and methyl radical. In the present study, the plasma chemical-vapor deposition process using CH₄/H₂ gas was considered. The reactions with vapor CH₃ radicals on the terrace (dimer mechanism) and at the SB step (trough mechanism) were investigated. The desorption of hydrogen from the step edge is easier than that from the terrace. It is expected that the concentration of the surface dangling bond at the step edge is higher than that on the terrace; therefore, the CH₃ radical is preferentially adsorbed at the step edge. The H abstraction from the CH₃ group at the step edge is easier than that on the terrace due to the steric repulsion with the adjacent H atom. The C₂H₅ group is formed on the surface as a by-product with the CH₃ adsorption at the CH₂ group.