Formation of ion tracks in amorphous silicon nitride films with MeV C 60 ions

Amorphous silicon nitride (a-SiN) films (thickness 5–100nm) were irradiated with 0.12–5MeV C60, 100MeV Xe, 200MeV Kr, and 200 and 420MeV Au ions. Ion tracks were clearly observed using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) except for 100MeV Xe and 200MeV Kr. The observed HAADF-STEM images showed that the ion tracks consist of a low density core (0.5–2nm in radius) and a high density shell (several nm in radius). The observed core and shell radii are not simply correlated with the electronic energy loss indicating that the nuclear energy loss plays an important role in the both core and shell formations. The observed track radii were well reproduced by the unified thermal spike model with two thresholds for shell and core formations.