Orientation dependent annealing kinetics of ion tracks in c-SiO₂

The structure and thermal response of amorphous ion tracks formed along the $[112¯0]$⁠, $[101¯0]$⁠, and [0001]-directions in crystalline quartz have been investigated using small angle x-ray scattering. The radii of the ion tracks vary by about 5% (0.3 nm) for tracks along different crystallographic directions. Molecular dynamics simulations reproduce this anisotropy along the $[101¯0]$ and [0001] directions and suggest that differences in thermal conductivity along these directions are partly responsible for this observation. Using in situ annealing, tracks along the $[101¯0]$ and [0001] directions were shown to recrystallize during thermal annealing around 960–1020 °C with activations energies around 6 eV, while those along the $[112¯0]$-direction already disappeared at 640 °C with a significantly lower activation energy around 3–4 eV.