Ion-induced surface pattern evolution in computer simulations with a new approach – unification of collision cascade and kinetic 3D Monte Carlo calculations

Aiming at a more complete but still efficient atomistic calculation of the action of low-energy ion impacts on surfaces, a novel program package has been developed which unifies the calculation of the collision cascade with kinetic 3D Monte Carlo simulations. The 3D atom relocations by the collision cascade were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Here, we analyse the impact of bulk processes like vacancy and interstitial creation, defects annihilation and migration as well as ion erosion on surface morphology. In particular, we prove the importance of a complete description of the ion impacts. Collisional and thermally activated processes occurring simultaneously are important for the ripple formation and propagation. The novel program was applied to ripple formation on Si substrates under 1 keV Ar+ irradiation for fluences up to a few 10¹⁸ cm^-2. Besides the angle of ion incidence, the crucial parameters deciding about ripple coarsening are migration energies of surface defects.
So far, simulation cell sizes of 100x100x50 nm³ with about 17 million atoms allow ripple formation up to 25 nm wavelength, thus direct comparison with experiment can be done.
Additionally, the scaling behaviour of the surface pattern wavelength and roughness has been studied.