Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Poster: Oxide and Insulator surfaces: Structure, Epitaxy, Growth and Adsorption

O 44.8: Poster

Dienstag, 13. März 2018, 18:15–20:30, Poster A

LEED I(V) analysis of the physisorption system C₂H₂ (3√2×√2)R45^∘/NaCl(100) — •Jochen Vogt — Chemisches Institut der Uni Magdeburg, Magdeburg, Germany

The first layer acetylene adsorbed on the NaCl(100) surface is known to form long-range ordered structures with (3√2×√2)R45^∘ and (7√2×√2)R45^∘ translational symmetry, respectively [1,2]. The comparatively large unit cells in this system are assumed to be induced by a moderate lattice mismatch with the substrate. In both cases, however, the adsorbate structure is not known in full detail. The poster presents first results of an I(V) structure analysis for the (3√2×√2)R45^∘ phase. Calculated full dynamical LEED intensities are fitted to experimental data of seven diffraction spot orders. An unusual feature of the in-house search algorithm for R-factor minima is the use of rigid molecule structure parameters instead of individual atomic site coordinates, with the advantage of a reduced number of free parameters. According to LEED (Pendry R-factor=0.27), the substrate exhibits a small site specific surface rumpling. The acetylene molecules are placed in average 2.71 Å above the Na⁺ ions in a nearly parallel orientation with respect to the surface plane. Lattice mismatch induced strain appears to be released by small lateral shifts of the molecules from the exact on-top positions over Na⁺.

[1] A. Glebov, R. Miller, J. P. Toennies, J. Chem. Phys. 106 (1997) 6499. [2] A. G. Cabello-Cartagena, J. Vogt, H. Weiss, J. Chem. Phys. 132 (2010), 74706.