Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)

O 14.24: Poster

Monday, March 27, 2006, 18:00–21:00, P2

PIRS and LEED study of quasi-orthorhombic acetylene thin films on KCl(100) — •Jochen Vogt and Helmut Weiss — Chemisches Institut der Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany

The epitaxial growth of acetylene thin films on KCl(100) single crystal surfaces has been studied by means of low-energy electron diffraction (LEED) and polarization infrared spectroscopy (PIRS) in transmission geometry at 40 K. IR spectra in the regions of the infrared active fundamentals ν₃ and ν₅ were recorded at increasing coverages up to 20 layers. In both cases a triplet structure of the spectra was observed. LEED experiments without extensive adsorbate charging effects were possible up to coverages of 4 layers and indicated a (√2×√2)R45^∘ symmetry, consistent with the results of helium atom diffraction experiments [1]. All experiments support a parallel orientation of the molecules in the layers, as expected for the low-temperature orthorhombic phase of C₂H₂. Based on the structure model of this phase the PIRS film spectra were analyzed using a dynamic dipole-dipole coupling model. Good agreement between simulated and experimental spectra is obtained for both fundamental modes if the possibility of azimuthal misorientations of adjacent layers by 90^∘ is taken into account.

[1] J. P. Toennies et al., Phys. Rev. B 65, 165427 (2002)