The implantation of 50 or 100eV Si atoms into (100) 2 x 1, (110) and (111) monocrystals, and the resultant damage, were studied by using molecular dynamics simulations. It was predicted that low-energy ion irradiation would create near-surface disordered zones. For 100eV bombardment, they contained some 15 displaced atoms. The latter number depended only slightly upon the surface crystallography. The cross-sectional size of the disordered zones was compatible with experimental data on the amorphization fluence of Si under low-energy bombardment if amorphization was assumed to proceed via the overlap of single-ion impact-induced amorphous zones. The amorphous zones were metastable, and crystallized at sufficiently high temperatures and/or after sufficiently long times. Point defects were left behind at the surface. For a particular case study which was investigated, collapse of the amorphous zone was characterized by an activation energy of some 3eV. Amorphous zones could therefore be long-lived at room temperature, on the time-scale of an experiment. Disordered atoms were detected by invoking a geometrical criterion. That is, every atom that was located outside of a sphere with a radius that was equal to the Lindemann radius was said to be disordered. The number of true interstitials (atoms that were more than half a nearest-neighbor distance from an ideal lattice site) was proportional to the number of disordered atoms. The latter number could be described by dividing the projectile energy by an amorphization energy of 6 to 7eV. This value was in agreement with other simulations, and with experimental data. Except in the case of the open (110) surface, the crystal damage reached to considerably greater depths than the ion range.

H.Hensel, H.M.Urbassek: Physical Review B, 1998, 57[8], 4756-63