First principles investigations of diamond ultrananocrystals

Presented here are results of ab initio Density Functional Theory (DFT) structural relaxations performed on dehydrogenated and monohydrogenated nanocrystalline diamond structures of octahedral {111} and cuboctahedral morphologies, up to approximately 2 nm in diameter. Our results in this size range show an inward transition of dehydrogenated nanodiamond clusters into carbon onion-like structures, with preferential exfoliation of the (111) surfaces, in agreement with experimental observations. However, we have found that this transition may be prevented by monohydrogenation of the surfaces. Bonding of atoms in the surface layers of the relaxed structures, and interlayer bonding has been investigated using the electron charge density.