THEORETICAL-STUDIES OF DIAMOND MECHANOSYNTHESIS REACTIONS

Density functional theory methods have been used to examine the intera ction of (i) the carbene and C-2 tools With a pair of radical sites on the diamond (111) surface and (ii) the carbene tool with a surface di mer on the reconstructed diamond (100) surface. For the (111) surface, the carbene tool (carbenecyclopropene) is found to bond preferentiall y to a single radical site (on top site) rather than at a bridged site . This means this tool is not useful for adding a carbon to diamond (1 11) at this site. The C-2 tool, on the other hand, is found to add a b ridged C-2 molecule, through a series of steps which are overall exoth ermic. The carbene tool can add a carbon to the bridged C-2 molecule, leading to a bridged C-3 molecule perpendicular to the surface, by an overall exothermic series of steps. If another radical site is activat ed, the C-3 can bend over to a threefold coordinated position, with on ly a small barrier. Thus, this series of steps can be used to create a threefold coordinated C-3 molecule on the diamond (Ill)surface. For t he surface dimer on the reconstructed (100) surface, the carbene tool is found to add with no barrier if the angle between the tool and the surface is allowed to vary or with a 0.09 aJ (13 kcal mol(-1)) barrier for a C-2 upsilon constrained approach. In this case, a bridged site is strongly favored, and the subsequent steps of sequentially breaking the pi and sigma bonds between the tool and added carbon atom are all feasible. Thus, this series of steps can add a bridged C atom to the reconstructed diamond (100) surface.