Simulation of cluster impacts on silicon surface

A new hybrid model, combining Molecular Dynamics (MD) with continuum mechanics and thermodynamics, has been developed for studying collisions of energetic particles with a solid surface. MD describes interaction of atoms in the central impact zone characterized by energetic atomic collisions and non-equilibrium states of matter while the continuum model is applied to a much larger volume outside. Appropriate boundary conditions at the interface of the two regions prevent the appearance of unphysical shock wave reflections. The hybrid model is very efficient in computations as it reduces the number of the system's degrees of freedom by minimizing the size of the central MD zone. The model was applied to collisions of a few keV Ar clusters containing approximately 100 atoms with Si(100) surface. The results show that cluster impacts create craters and local melting and that a number of displaced surface atoms have large lateral velocities. The latter may explain the experimentally observed surface smoothing by cluster bombardment.