COMPUTER-SIMULATIONS OF ION-SCATTERING AND RECOILING BLOCKING PATTERNS FOR SURFACE-STRUCTURE ANALYSIS

A three-dimensional classical ion trajectory simulation code has been developed and applied to ion scattering and recoiling patterns on a la rge-area detector. The test systems used for the patterns were as foll ows: (1) Pt{110}-(1 x 2) and -(1 x 3) as an example of a reconstructed metal surface; (2) Ni{100}, {110}, and {111} surfaces as an example o f different crystal faces; and (3) Ni{110}-(2 x 1)-O as an example of adsorbate recoiling. The optimum experimental configurations for colle cting data for structural analysis have been considered. Three configu rations have been identified; these include collection of both in- and out-of-plane scattering and recoiling data. The anisotropic patterns obtained for the scattered I(S) and recoiled I(R) flux in azimuthal de lta and exit beta angle space are produced by blocking cones and are u nique for the specific substrate and adsorbate structures. Critical ex it beta(c) and azimuthal delta(c) angles can be identified from these patterns. The interatomic spacings d along specific azimuths are deter mined from measurements of beta(c) and delta(c). Simulated patterns fo r the three test systems listed above are presented and their features are analyzed in terms of the surface structures. The advantages and n ew features available through the use of large-area detectors are desc ribed and compared to conventional ion scattering spectrometry (ISS). In the case of Pt, for which comparable experimental scattering data a re available, the agreement between simulations and experimental resul ts is good.