Molecular dynamics simulation of swift ion damage in lithium fluoride

Abstract

A model of an ion explosion spike initiated within the framework of the virtual photon model by the passage of a swift ion through a crystal of lithium fluoride comprising 6400 ion pairs, which is followed by Auger emission is described in outline. The repulsive Coulomb interaction of the so-called spike ions thus created amounts to 19.746 keV/nm of trajectory. The resulting Coulomb explosion ejects spike ions into interstitial sites, but principally embodies a collective inward movement of lattice anions accompanied by outward motion of cations. In 〈1 0 0〉 this results in disorderly collisions within 10 fs, but in 〈1 1 0〉 the motion is more coherent, indeed the collective relative oscillation of the two sub-lattices is of sufficient amplitude transiently to form crystalline, high energy, non-cubic structures. Spike ion discharge spanning 300 fs generates F-atoms (F 2 − species) mainly in a central disordered zone. As the system cools, this zone contracts and exceptionally in the present case generates a pair of pinned edge dislocations. The dislocations are very stable and do not mutually annihilate until they have been heat-treated for some time at 30 K below the nominal melting point. The defects thus created would etch to form pits as originally described by the author some years ago. Hillocks as first described by Knorr, but more recently studied in detail at Darmstadt are also formed.