DIAMOND EPITAXY ON A SI(001) SUBSTRATE - A COMPARISON OF STRUCTURAL MODELS

A previous proposal for the atomic structure at the interface of a diamond (001) adfilm growing epitaxially on Si(001) in a 45 degree rotated orientation, is extended by the inclusion of Si atoms in the second adfilm layer. In addition, two new models for growth in 3:2 registry in a parallel orientation are investigated, including versions with and without incorporation of hydrogen atoms into the structure. For each model, a total energy optimisation of the geometry is carried out using quantum chemical calculations with the PM3 Hamiltonian applied to periodically repeated atomic clusters containing up to eight atomic layers. Due to the non-stoichiometric nature of the interface layers, comparisons of the relative energetics of the models are performed by the introduction of carefully defined interface and adhesive bonding energies. It is found that the rotated model has a very low intrinsic interface energy and is favourable for very thin adfilms, but due to the smaller elastic deformation needed for registry the parallel growth mode becomes most favourable for thicker layers. Detailed atomic geometries for the optimised structures of all three models are given.