Latent track formation in silicon irradiated by 30 MeV fullerenes

It is now well accepted that electronic excitation and ionisation arising f rom the slowing-down of swift heavy ions can lead to structural modificatio ns in most targets. It is shown here that new effects take place during irr adiations with high energy fullerene beams. Electron microscopy observation s were performed at room temperature on prethinned monocrystalline silicon samples after irradiation with 30 MeV fullerene ions. The observed damage i s continuous and confined around the projectile paths. The tracks consist o f amorphous material as shown by high resolution transmission electron micr oscopy observations. These tracks recrystallize very rapidly in the electro n microscope during the observations in high resolution conditions. Further more, a decrease of the track diameter is observed as the cluster ions pene trate deeper inside the target, which is related to an angular scattering o f the cluster constituents. At large penetration depths, before disappearin g completely, the tracks end as aligned damaged regions of decreasing diame ters. Finally, strong sputtering effects occur on the target surfaces, so t hat craters are generated at the impacts of the projectiles. The fact that amorphous tracks are generated in crystalline silicon following heavy clust er bombardment can be attributed to the strong localization of the deposite d energy during the slowing-down process of rather slow projectiles. (C) 19 98 Elsevier Science B.V. All rights reserved.