Surface relaxation and rumpling of RbI(001) determined by medium energy ion scattering

The surface relaxation and rumpling of RbI(001) were determined directly by medium energy ion scattering using a new toroidal electrostatic analyzer. Its energy resolution was estimated to be 1 x 10(-3), which allows a layer-by-layer analysis of a near surface region. We measured the angular spectra of the ion scattering yields for I- around the [011] axis in the (100) plane and around the [111] axis in the (110) plane using well-collimated 80 keV He+ beams. The angular shifts of the scattering yield minima for I- of the second layer from those for I- of the deeper layers, giving quantitative information about the surface relaxation and rumpling. The present analysis revealed that the location of the top Rb+ and I- ions was shifted by 0.080 +/- 0.033 Angstrom toward the inside and by 0.001 +/- 0.014 Angstrom toward the vacuum side, respectively from the non-relaxed lattice position in the surface normal direction. The results are compared with the theoretical calculations based on shell models and a molecular dynamics simulation. (C) 1998 Elsevier Science B.V. All rights reserved.