Wataru Takeuchi

Influence of thermal vibrations on ion surface scattering near 180° scattering angle in the two-atom scattering model☆

Abstract Based on the two-atom scattering model, the ion surface scattering near 180° scattering angle is investigated for the analysis of a new ion beam technique, i.e., impact collision ion scattering spectroscopy (ICISS). The shadowing effect of elastic scattering and the ion trajectory focusing effect play important roles for large-angle backscattering at the solid surface. Numerical results show that these two effects are very sensitive to the thermal vibrations of surface atoms, especially to their anisotropy. The angle of incidence at the maximum intensity and the peak width (fwhm) of the backscattering intensity is an increasing function of uz/ux, where ux and uz are the rms displacements parallel to and perpendicular to the surface, respectively. In the case of a TiC crystal, it was found that the ratio of uz/ux is nearly 1.6.

Shell correction of screening length in interatomic potential

Abstract In the computer studies on the interaction of an charged particle with solids, authors treat the nuclear collision by the Thomas–Fermi screened Coulomb potential. For better agreement with experiment, authors sometimes modify the screening length. We investigate the theoretical background for the correction factor of the screening length in the interatomic potential which is deduced from two steps. The first step is to determine the correction factor of an isolated atom so as to adjust the average radius of the Thomas–Fermi electron distribution to that of the Hartree–Fock electron distribution. The second step is to determine the screening length of two-atom encounter, using the combination formula corresponding to the Firsov formula. The obtained correction factors of the screening length are in good agreement with those determined by the ICISS computer analysis.

Computer studies of 180° Ne neutral atoms backscattered from a Pt(111) surface

Abstract The 180° neutral impact-collision ion scattering spectroscopy (NICISS) intensity has been evaluated using the ACOCT program code based on the binary collision approximation. The computer simulations are performed for the case of 2 keV Ne+ ions incident along the [ 1 1 2] direction of a Pt(111) surface. It is found that there are the influences of not only first or second layer atoms at the surface but also several layer atoms below the surface on the 180° Ne NICISS intensity. Also, the ACOCT results show that the Moliere approximation of the Thomas-Fermi potential with a reduced Firsov screening length multiplied by a factor of 0.85 and the vertical component of surface Debye temperature 143 K are suitable for the 180° Ne NICISS intensity at the Pt(111) surface.

Computer studies of surface structure of NiA1(111)

Abstract The 180° neutral impact-collision ion scattering spectroscopy (NICISS) data have been analyzed using the ACOCT program code based on the binary collision approximation (BCA) The computer simulations are performed for the case of 2 keV He + ions incident along the [121] direction of a NiA1(111) surface. It is found that the experimental results are well reproduced by the ACOCT simulations including the inward relaxation of 40% of the first interlayer spacing on Ni terminated layer at the NiA1(111) surface and including the Moliere approximation of the Thomas-Fermi potential with a reduced Firsov screening length, multiplied by a factor of 0.60.

Energy spectrum of He+ ions scattered from the SnTe(001) surface

Abstract The energy spectra of He + ions specularly reflected from a SnTe crystal with the rocksalt structure have been calculated using the ACOCT computer code based on the binary collision approximation. The calculations are performed for 700 keV He + ions incident along the aligned [210] direction and the random one of a SnTe(001) surface at glancing angles. The calculated spectra for the [210] direction have several peaks which are attributed to the surface hyperchanneled ions reflected from the first layer, and the energy spectra of the random direction have only one peak due to the ions reflected from the first layer. An interesting aspect of measured spectra is that the half-width of the energy spectrum for the [210] direction is larger than that of the random one. These broad spectra of the [210] direction are found to be due to the surface hyperchanneled ions.