Ejection of atoms from rare-gas solids by low energy cascades

Abstract

The results of a molecular dynamics calculation are presented for collisional ejection of atoms from excited low temperature rare-gas solids. An atom in the solid is assumed to receive an amount of kinetic energy consistent with an energetic, non-radiative decay of an excited dimer and the number, energy and direction of ejected atoms are calculated as functions of depth in the solid of the initially energized atom. The results are compared to the standard binary-collision cascade model and to a thermal-spike model for ejection. The yields integrated over depth are found to depend nearly linearly on energy deposition as in the collision cascade model. They also scale with the surface number density and the surface binding energy. The calculated angular and energy distributions are relatively insensitive to the exciting energies and exhibit distinct differences from the cascade and thermal models. However, the peak position in the energy spectra is consistent with the cascade model if the surface binding energy, which is about two thirds the cohesive energy for these solids, is used. Experimental results on the electronic sputtering of solid argon are briefly considered.