Morphological changes of nanostructures on silicon induced by C₆₀-ion irradiation

We study morphological changes on the Si surface induced by the C₆₀ ion beam under various irradiation conditions. The fluence and incident energy of the C₆₀ ion beam was 1 × 10¹⁶–1 × 10¹⁹ ions/m² and 50 keV–9 MeV, respectively. The beam’s incident angle to the surface normal was 0° or 60°. As a result of the changes in these variables, three types of nanostructures were observed: concave and convex, stringlike, and ripple structures. Structure shapes or sizes varied with changes in the parameters. Almost all cases showed concave and convex structures at an incident angle of 0°. At a 60° incident angle, stringlike or ripple structures were formed. Stringlike structures were formed at higher incident energy, while ripple structures were formed at lower incident energy. We found that both stringlike and ripple structures can form from sputtering and thermal effects. The formation of string structure requires a thicker amorphous layer and the proper balance of sputtering and annealing.