For bulk samples of diamond NPs, conversion to nano-onions is often done by high temperature annealing. At T > 1000 K, surface reconstructions are known to occur that force carbon atom dimerization. The reconstructed diamond surface is thought to contain little to zero hydrogen, and thus promotes graphitization by reducing cleavage energies by ~50%. The other factor is the surface itself, where different planes graphitize at varying rates. In the range of 1400 -1900 K, the (111) surface is considered the most reactive, due to its buckled hexagons,with dimensions similar to hexagons in graphite (0001). This factor is proposed to promote cleavage and exfoliation of graphite-like layers that encapsulate the diamond NP.