Track formation in amorphous metals under swift heavy ion bombardment

Recently tracks were observed in amorphous metals irradiated by swift multicharged ion (MCI). The experiment is especially interesting because the track was not revealed if amorphous metal target had been annealed preliminarily. The present paper is devoted to interpretation of the experimental data in terms of the so-called "plasma model". The slowing down of MCI in solids results from the energy loss mainly due to inelastic collisions. Practically almost all energy inputs by projectile are concentrated in excited electrons resulting from ionization processes. The relaxation of the excited electrons happens due to electron-electronic (electronic heat conductivity) and electron-lattice collisions. The cooling time of the excited electron subsystem itself in metals is some orders of magnitude smaller than the typical time of energy transfer from electrons to the lattice which is depended essentially on crystal structure of the target. The rate of electron energy transfer to target atoms is determined by the presence (in single crystals) or the absence (in amorphous metals) of the lattice periodic potential. The melting track should be observed in amorphous target with metallic conductivity, as here the rate of electron energy transfer is more than in single crystal. Crystallisation happens upon annealing, amorphous metal turn into crystal with periodic potential and tracks are not formed. The calculations of final lattice temperature taking into account the increase of melting point at local fusion and lattice thermal conductivity are carried out. (C) 1998 Elsevier Science B.V. All rights reserved.