EM study of latent track morphology in TiO2 single crystals

A TEM investigation was conducted into the morphology of 167 MeV Xe (2 × 1010 cm−2 to 1014 cm−2) and 1 GeV Bi ion (2 × 1010 cm−2) induced latent tracks in single crystal TiO2 (rutile). At fluences up to 1011 cm−2 latent tracks are visible as discontinuous lines of strained crystal along the ion trajectory. From the implanted surface down to about 60–70 nm below the surface the tracks appear as continuous conical structures with a base of diameter 5–6 nm (Xe) and 8–9 nm (Bi) in contact with the surface with a mushroom shaped hillock extending outward from the surface. At fluences between 6 × 1012 cm−2 and 1013 cm−2 the crystal is amorphized but rod-like crystalline regions remain which are oriented along the ion trajectories. Amorphization extends from the surface down to 8.3 μm below suggesting an upper limit for the threshold electronic stopping power for amorphization of 7.3 keV nm−1. At 1014 cm−2 Xe the entire 8.3 μm subsurface region is rendered amorphous although some evidence of short range ordering remains.