HYPOTHETICAL C-100 MOLECULE AND DIAMOND-GRAPHITE INTERFACE - UNSTABLEAND METASTABLE STATES OF CARBON

We summarise our ab initio calculations on diamond to date and their c onsequences for diamond film growth. Local spin density calculations o n 50 and 62 atom clusters have given good estimates for hydrogenation reactions including activation energies and surface reconstructions. L arger calculations on the icosahedral, tetrahedrally bonded C-100 mole cule reveal it should spontaneously decompose into two concentric full erenes (C-20 and C-80). It is possible that a similar mechanism might cause graphitisation at a diamond asperity if hydrogen were not presen t, at least where a twin boundary meets the surface. However, the satu rated, tetrahedrally bonded C100H60 molecule was found to be stable, e legantly illustrating one of the much discussed roles of hydrogen in d iamond growth. We have tested the graphite-diamond interface model of Lambrecht et al. (Nature, 364 (1993) 607-610) and find the interface t o be stable, but less so than their interatomic potential calculations suggested. We find some evidence for bond reconstruction and basal di slocation formation.