Molecular dynamics simulation of argon cluster ion collisions with argon atoms

The process of collisions of accelerated argon cluster ions with residual gas atoms was analyzed by molecular dynamic simulation. The cluster ions under consideration had an icosahedral structure. Their initial temperature was assumed to be equal to 35 K. The influence of the value of accelerating potential and initial size of cluster ions on the results of their impact breaking is investigated. The number of atoms in cluster ions varied from 309 to 1415. The accelerating potential value varied in the range from 10 to 100 keV. An evolution of cluster ions after the collision was observed for 1.51 mu s. The simulation showed that after collisions, fragments of cluster ions can be survived, whose size, temperature and phase state (partial or complete melting) are determined by the ratio of the two above-mentioned parameters. Subsequent intensive evaporative cooling of these fragments leads to the full recovery of an ordered structure in them: icosahedral or crystalline. By the end of the considered time interval, temperature and size decrease of the fragments due to evaporation significantly slows down. It was also found that with weak or moderate damage of cluster ions, the processes occurring at the initial stage of the fragment formation (several dozen picoseconds) have a vibration nature. The frequency of these vibrations in the considered variants was in the range of 220-285 GHz. In addition, the parameters for atom scattering both knocked out from cluster ions at collisions and those leaving the fragments during evaporation were determined. The simulation results were used to investigate the formation process of so-called accelerated neutral atom beams, which arise by interaction of gas cluster ion beams with residual gas. Assumptions were made about the composition of the formed beams.