Dependence of cluster ranges on target cohesive energy: Molecular-dynamics study of energetic Au_(402) cluster impacts

摘要

It has long been known that the stopping and ranges of atoms and clusters depends on the projectile-target atom mass ratio. Recently, Carroll et al. [S.J. Carroll, P.D. Nellist, R.E. Palmer, S. Hobday, R. Smith, Phys. Rev. Lett. 84 (2000) 2654] proposed that the stopping of clusters also depends on the cohesive energy of the target. We investigate this dependence using a series of molecular-dynamics simulations, in which we systematically change the target cohesive energy, while keeping all other parameters fixed. We focus on the specific case of Au_(402) cluster impact on van-der-Waals bonded targets. As target, we employ Lennard-Jones materials based on the parameters of Ar, but for which we vary the cohesive energy artificially up to a factor of 20. We show that for small impact energies, E_0 approx< 100 eV/ atom, the range D depends on the target cohesive energy U, D ∝ U~(-β). The exponent β increases with decreasing projectile energy and assumes values up to β = 0.25 for E_0 = 10 eV/atom. For higher impact energies, the cluster range becomes independent of the target cohesive energy. These results have their origin in the so-called 'clearing-the way' effect of the heavy Au_(402) cluster; this effect is strongly reduced for E_0 approx> 100 eV/atom when projectile fragmentation sets in, and the fragments are stopped independently of each other. These results are relevant for studies of cluster stopping and ranges in soft matter.