Angular dependence of the backscattering yield from Si crystals in double and single alignment

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Abstract
Single and double alignment backscatterings of MeV helium ions from a silicon crystal have been simulated in a computer. Angular dependences of the backscattering yield in a (110) plane for 2 MeV helium ions along (110), (100), and (111) are calculated for regular lattice positions and various interstitial positions in single alignment. In double alignment 2.8 MeV helium ions are incident on a (100) crystal plane parallel to (110) and angular dependences of the backscattering yield for detector rotation in a (110) plane along [110], [111] and [010] are calculated. In (110) and [110] the tetrahedral (T), the hexahedral (H) and so called ytterbium atom positions (Y) show a flux peak and the split (100) and the bond-centred positions (BC) have a shallow and narrow dip. In (111) and [111] the H-and the BC-positions have a flux peak and the other positions a dip. In (100) (or [010]) the BC-, H-, Y-, S-positions (BC and H) show characteristic off axis peaks and the others a dip. In double alignment the reduction in the backscattering yield for regular lattice positions (by a factor of 10−3) and the enhancement in the yields for the interstitial positions (by a factor of 2–6) enable one to locate host interstitial atoms over an interstitial fraction of 10−3. The single alignment yield calculations are compared with the experimental results by Andersen and coworkers and by lue and coworkers.