TRACK INTERFERENCE IN SWIFT HEAVY ION IRRADIATED Al2O3

Abstract

The morphology of latent ion tracks induced by high energy heavy ions in Al2O3 have been studied using a combination of high resolution TEM (HRTEM), exit wave reconstruction, geometric phase analysis and numerical simulations. Single crystal α-Al2O3 crystals were irradiated with 167 MeV Xe ions along the c-axis to fluences between 1 x 1010 and 1 x 1013 cm-2. Planar TEM lamella were prepared by FIB and geometrical phase analysis was performed on the phase image of the reconstructed complex electron wave at the specimen exit surface in order to estimate the latent strain around individual track cores. In addition to the experiments, the material excitation in a SHI track was numerically simulated combining Monte-Carlo code describing the excitation of the electronic subsystem with classical molecular dynamics of the lattice atoms. Experiment and calculation both demonstrated that the relaxation of the excess lattice energy results in the formation of a cylinder-like disordered region of about 4 nm in diameter consisting of an underdense core surrounded by an overdense shell. Modeling of the passage of a second ion in the vicinity of this disordered region revealed that this damaged area can be restored to a near damage free state. The estimation of a maximal effective distance of recrystallization between the ion trajectories yields values of about 6 - 6.5 nm which are of the same order of magnitude as those estimated from the saturation density of latent ion tracks detected by TEM.