Molecular dynamics (MD) simulations of 500 eV  Xe⁺ ion bombardment of Si (001) at 67° ion incidence angle  delivers typical distributions of displaced near surface Si atoms. We focused on the spatial distributions of surface vacancy and adatom generation on Si (001) surface.

After 500 MD simulations of single Xe⁺ ion impacts, the mean distribution can be fitted by Gaussian distribution of different aspect ratio. The center of the distribution is ~15 nm from the impact point. Then we performed 3D kinetic lattice Monte-Carlo simulations using this defect distribution as input. 

Initially, the surface was simply homogeneously roughened, and after a fluence of about 3 x 10¹⁵ ion/cm²  the surface started to form ripple pattern perpendicular to the azimutal incidence angle with wavelength ~15 nm. The ripple moves forward in ion incidence direction. These results agree nicely with experimental observation. The mechanism of ripple formation related to surface atomic flows induced by ions, surface damage distribution and Mullin’s diffusion will be discussed.