Stability of Nanodiamond

The theoretical and computational studies outlined in this chapter focus on the phase transitions among nanodiamond, graphitic, and fullerenic forms of nanocarbon. Computationally, these transitions are represented by quantum mechanical methods, and the transformations have been modeled using a variety of cluster geometries and sizes. The range indicates that outside this range, the nanodiamonds will be metastable with respect to a transformation to graphitic or fullerenic phases. The identification of a co-existence region indicates that the phase transitions are not entirely thermodynamically driven, and that other factors such as surface energies, surface stress and charge, and kinetic considerations, may be instrumental in inducing a change of phase. One property, fundamental to the stability of nanodiamond, is the degree of surface hydrogenation. A logical explanation is that although H-terminated nanodiamonds may be slightly higher in energy than their dehydrogenated counterparts, they are metastable below the hydrogen desorption temperature, and there will be no spontaneous hydrogen desorption, and recombination without a suitable driving force.