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Structure analysis of crystal surfaces by low energy ion beams

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Publication Date
DOI: 10.1016/0168-583x(88)90703-3


Abstract The impact collision mode of low-energy ion scattering (ICISS) with backscattering close to- and at 180 ° has been used to determine the surface structure of single crystals in a direct and straightforward way. The intensity of backscattered primary particles (noble gas ions and neutrals — NICISS, or alkali ions — ALICISS) are measured as a function of the polar and azimuthai angles with respect to the surface, supplying a real space image of the atom positions. Energy discrimination by means of a time of flight or electrostatic deflection technique, respectively makes the method surface mass selective. On the basis of shadowing (and blocking) of the primary particles the location of atoms in the surface near region has been determined, the reconstruction of several fcc (110) metal surfaces have been found to be of the missing row type. The NICISS method has also clear benefits for surface crystallographic investigation of binary component systems. The NiAl(111) surface consists of two types of surfaces, either Ni or Al terminated, separated by single steps. From NICISS survey patterns the complete information of surface and near surface “bulk” crystallography may be displayed in a single gray scale plot. For 'the As/Si(001) −1 × 2 surface an As overlayer consisting of As dimers with an interatomic distance of 2.55 Å has been found.

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