Molecular Dynamics Simulations of Nanodiamond Graphitization

Nanocarbons have attracted great interest due to their potential applications in nanoscale devices, medicine, lubrication and composite materials. Recently, nanocarbons with a variety of morphologies are reported to have been obtained after annealing nanodiamonds above 1,200 K. Here, we have investigated the transformation of 2–5 nm nanodiamond particles upon annealing using molecular dynamics simulations. The simulations show that nanodiamonds undergo annealing-induced graphitization by a progressive sp3 to sp2 conversion of carbon atoms that begins at the surface. The extent of this conversion depends on the size and morphology of the nanodiamond. It is found that while graphitization proceeds easily from {111} surfaces towards the core, the presence of {100} surfaces leads to residual sp3 carbon atoms. We will also discuss different steps involved in nanodiamond graphitization, the formation of onion-like carbon and vibrational spectra of these structures.