Computer simulation of radiation-stimulated fragmentation of nano-sized clusters of semiconductors

Full text: The investigation of clusters of semiconductor materials has been the subject of great interest due to their unique properties that cardinally differs from those of bulk materials. Research on dependence of cluster properties on its size, charge states and stoichiometry is of obvious interest. In addition, processes of formation and fragmentation of clusters are rather complicated and have been insufficiently studied, particularly in respect of clarifying of the role of irradiation in these processes. Here we have simulated the structure and properties of GamAsn and Sin clusters in different charge states (positive, neutral, and negative), as well as possible channels of their disintegration by the computational approach that combines molecular dynamics and self-consistent tight-binding methods. It has been revealed, for example, that for 4- and 5-atom clusters GamAsn there are four possible stable geometries depending on their charge state and stoichiometry. The anions GamAsn are found to be more stable with respect to disintegration. The probability of fragmentation is large for the positive and neutral clusters of GaAs4, Ga2As3, Ga3As2, especially for Ga2As3, the neutral ones disintegrate into two opposite-charged fragments with more probability. Thus, the charged clusters may constitute considerable part of produced clusters due to their more stability than neutral ones in respect of disintegration, moreover, the additional charged clusters appear in result of disintegration of neutrals ones. The process of fragmentation of a number of clusters caused by the multiple ionization of an atom and then the whole cluster has been simulated. Such ionization can be triggered by irradiation with both high-energy X-rays and charged nuclear particles. The kinetic energy changes of the cluster with the time are obtained by molecular dynamic simulation of the time evolution of system It is shown that the multiple ionization of the cluster itself exerts a greater influence on cluster destruction than the single multicharged ion alone. For instance, the twofold-charged cluster [Ga2As2]+2 disintegrates in three daughter fragments, exactly, two positive Ga+ ions and one As2 molecule