Acoustic activation of structural rearrangement in carbon coating by ion bombardment

In order to explain atomic rearrangements in the target material, which is far deeper than the penetration depth of implanted ions, the acoustic action of low-energy (≤ 1 keV) ions on point defects in a diamond-like carbon (DLC) target was investigated. The total amplitude of the stress pulse generated due to the transfer of energy, momentum and volume from an incident ion to the target material is found, using a spherical approximation of the thermoelastic peak — the nanometric region where the phonon energy loss of the ion is thermalized. The spatial dependence of the amplitude of the generated pulse adjusted for sound absorption follows a power law rather than an exponential law. Due to such long-range action, the acoustic pulses from the ions of C+, Ar+ and Xe+ bombarding the DLC target can activate migration of defects at depths up to 50 nm and considerably reduce the activation energy of kinetic process at depths up to 300 nm. The dependence of the maximum depth of defect activation on the type of defect and on the energy of the ion was investigated for two typical values of the activation energy. The model was used to explain experimental data concerning the modification of optical properties of amorphous sp2-bond carbon films by 1.2 keV Ar+ ions.