Damage threshold and structure of swift heavy ion tracks in Al₂O₃

Abstract

Structure changes and their formation threshold in swift heavy ion (SHI) tracks in Al2O3 are studied using a combined start-to-end numerical model. The hybrid approach consists of the Monte-Carlo code TREKIS, describing kinetics of the electronic subsystem, and classical Molecular Dynamics for lattice atoms. The developed approach is free from a posteriori fitting parameters. Simulations of Xe 167 MeV ion impacts show that relaxation of an excess lattice energy results in formation of a cylindrical discontinuous disordered region of about 2 nm in diameter. Recent transmission electron microscopy observations agree with these results. The threshold of an SHI track formation is estimated to be ~6.1 keV nm−1. Calculated x-ray diffraction patterns of irradiated material demonstrate more pronounced damage of the Al atoms sublattice near SHI trajectories. Modeling of Xe ion tracks overlapping demonstrates that the damaged area can be restored to a near virgin state. Estimations give 6.5 nm as the minimal distance between the Xe ion trajectories resulting in recovery of the transformed structure produced by the previous ion.

Recrystallization as the governing mechanism of ion track formation

“…Focused 30 keV Ga ion beam was used for milling and pre-thinning of samples, while 1 keV Ga ions were used for final polishing. Samples were imaged using JEOL ARM-200F TEM operating at 200 kV, achieving higher resolution than in the previous TEM analysis 16 .…”

“…It consists of well separable stages: excitation (at attosecond timescales) and relaxation (femtoseconds) of the electronic subsystem of a target, excitation of the lattice due to energy transfer from electrons (picoseconds), followed by structure changes during lattice relaxation (up to nanoseconds). In turn, the kinetics of structure transformations can be divided into: (a) formation of an initial damage around the ion trajectory, and (b) relaxation of this initial damage into a final damaged structure 16 . As with most of the multiscale physics problems, track formation cannot be traced accurately within a single model posing formidable challenges for theoretical description and understanding of the underlying physical mechanisms.…”

Fundamental Phenomena and Applications of Swift Heavy Ion Irradiations

“…A simplified and efficient model with no need of fitting parameters was recently proposed [281,282] and proved to be sufficiently accurate. In this approach, the atoms are modeled with MD simulations once they receive kinetic energy from electrons and holes which are described within the MC scheme as described above.…”

Latent tracks of swift Bi ions in Si3N4

“…To simulate the formation of Bi ion latent tracks a hybrid scheme was applied [7,8] for the coupled kinetics of the excitation and relaxation of the electronic and the atomic sub-systems of a material irradiated with highenergy heavy ions. First, the asymptotic trajectory Monte Carlo code TREKIS [9,10] is used to determine the initial parameters which are characteristic of an excited state of the ensemble of electrons as well as energy transferred to lattice atoms via electron-lattice coupling in an ion track.…”

“…The supercell sizes used in the MD simulations were 24.2×23.5×19.9 nm 3 (1096000 atoms) with the periodic boundary conditions in all directions. All details of the applied methods can be found in [7,13]. Track evolution is traced up to 150 ps, after which the cell temperature dropped below 350 K, so no structural changes are expected after this time.…”