Fig. 3: Ion energy dependences of (b) the mean track diameter and of (c) the mean track length in diamond.

In b, the track diameters determined from the top-views (0°) and the side-views are indicated by closed and open circles, respectively. The difference between them indicates the two-step structures of the tracks, whose candidate structures are schematically shown in (a) as surface craters and hillocks. In d, squared mean radii of the tracks determined from the side views are plotted against Se, indicating the track-formation threshold of 24 keV nm−1. In b–d, error bars represent the mean ± the standard deviation (SD), of more than fifty tracks for each condition.