Low energy cluster impact simulated by molecular dynamics; angular distribution of sputtering yield and impact under various impact angles

Abstract

The collision process of low energetic gold atoms and solid targets has been simulated using our molecular dynamics simulation code CLIMPACT II. The used algorithm is a third-order predictor Verlet algorithm [L. Verlet, Phys. Rev. 159 (1967) 98; W.F. van Gusteren and H.J.C. Berendsen, in: Molecular Liquids — Dynamics and Interfaces, A.J. Barnes et al., eds. (Reidel, 1984) p. 475.]. The iteration time step is continuously optimized by the program. About 50% of the total computer time is spent to integrate the motions during the first 100 fs of simulation time [B. Nitzschmann, Diploma thesis, Univ. of Oldenburg, Germany, 1992)]. When the crater formation ends and the motions in the target are slower, the step increases up to 20 times the start step size. Using this algorithm we are able to simulate a target of up to 10 5 particles. We use new nonreflecting boundary conditions. Only mechanical interactions are considered. The projectile can be chosen as a cluster with variable impact angle. Specifically the output yield under different impact angles and the distribution of the desorbed particles are presented and discussed. The temporal development of the desorption shows three distinct processes: an early explosive process, a surface ablation by an apparent surface shock wave, a final thermal evaporation.