Focused collision sequences in tungsten and molybdenum

Abstract

The resolution of momentum into focused collision sequences has been studied in the b.c.c. structure by observing the ejection of atoms from tungsten and molybdenum monocrystals undergoing irradiation with 50 kev A⁺ ions. The ejected atoms were collected on glass plates, and by analysing the form of the deposits it was found that ejection occurred preferentially in the and crystal directions. This is interpreted in terms of collision sequences travelling along these directions which, on intersecting the surface, cause ejection in the same direction. In order to obtain a qualitative understanding of the processes involved, some suggestions as to the possible focusing mechanisms are discussed, and approximate calculations of the relative focusing energies and ranges are shown to be consistent with the observed nature of the deposits. The appearance of faint streaks in the ejection patterns are explained in terms of the ejection of energetic recoil atoms whose trajectories are channelled between the {110} planes.