We present theoretical investigations of various hydrocarbon species adsorbed on hydrogenated flat (100), flat (111), and stepped (100) surfaces of diamond. We use ab initio density-functional molecular-dynamics simulations and a dynamical quenching minimization algorithm to calculate adsorption energies and minimum-energy configurations of different binding configurations. The onefold adsorption energies of the hydrocarbon fragments on all the surfaces were found to be in the order ${\mathit{E}}_{\mathrm{C}2\mathrm{}}$H>${\mathit{E}}_{\mathrm{CH}2\mathrm{}}$>${\mathit{E}}_{\mathrm{CH}3\mathrm{}}$>${\mathit{E}}_{\mathrm{C}2\mathrm{}}$${\mathrm{H}}_2$. C$ sub 2 roman H sub 2— is predicted to have stable twofold binding sites on both the terrace site and near step edges of the diamond (100) substrate. Adsorption on the flat (111) surface is found to be weaker compared to binding on the flat and stepped (100) substrates. We found several adsorption configurations where adsorption energies on the near step edges are different from those on the flat terrace. We studied local surface relaxations due to the adsorbed molecule. The binding of the hydrocarbon admolecule in the presence of an adsorbate is investigated. In general, we found weaker binding for molecules adsorbed on adjacent surface radical sites. Preliminary results on hydrocarbon adsorption at finite temperature are discussed.

• Received 19 May 1994

DOI:https://doi.org/10.1103/PhysRevB.50.15369