Surface effect on ion track formation in amorphous Si3N4 films

Thin films of amorphous Si3N4 (thickness 5-30 nm) were irradiated with 360-720 keV C602+ ions. Ion tracks were observed using transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The track length and the radial density profile of the track were measured for various combinations of the film thickness and the energy of C602+. The length of the ion track produced in a 30-nm film was found shorter than that in a 20-nm film indicating that there is surface effect on track formation. This can be qualitatively understood in terms of the energy dissipation process. The observed radial density profile also depends on the film thickness. The result can be explained by surface cratering.