Spherical carbon particles consisting of concentric graphite-like shells (carbon onion) can be formed by electron irradiation of graphitic carbon materials. Recent experiments have shown that heavy ion or electron irradiation induces the nucleation of diamond crystallites inside such concentric nested carbon fullerenes. In this work classical molecular dynamics simulations with an empirical many-body Brenner’s potential-energy expression developed for hydrocarbons are used to investigate irradiation effects on the process of transformation onion’s cores into diamond.

To explain contraction the spacing between layers in the carbon onions observed in experiments we propose model, which explains the transformation of faceted-layered structures into quasi-spherical graphitic onions under high electron irradiation. This model is based on the destruction of strained region, which include pentagonal rings and on filling the holes in different ways with heptagonal and pentagonal carbon rings. We have carried out calculation for three model of onion core and have obtained the temperatures and number of threefold atoms for the models. After comparing results of different models we could chose most perfect model for simulation of diamond-like structure nucleation. The temperature of transformation and the interlayer distances of this model are very close to the experimental values. Analyses of performed calculation give us the possibility to propose mechanism of formation of tetrahedral bonded carbon atoms inside a bucky onion. Our model can realistically describe almost all facts, which have been observed in experiments dealt with transformation of carbon onion core under electron irradiation.