Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)

O 18.53: Poster

Montag, 25. Februar 2008, 18:30–19:30, Poster F

Leed spot profile analysis of a quasi-one-dimensional system as a function of temperature — •Michael Cordin, Peter Amann, Enrico Doná, and Erminald Bertel — Institute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria

We employ low-energy electron diffraction (LEED) to investigate phase transition on the quasi-one-dimensional c(2x2)-Br/Pt(110) surface. Lowering the temperature yields a transition from a fluctuating, long range ordered phase at room temperature into an inhomogeneous state. From the LEED spot profile analysis we determine the temperature dependence of the fluctuations and the unusual reduction of the long range order parameter with falling temperature. Furthermore we observe the appearance of additional LEED spots corresponding to a primitive (2x1) and a (3x2) overstructure. The transition from the long-range ordered c(2x2) room temperature state to the inhomogeneous low-temperature state is completely reversible. The correlation length in the system is strongly anisotropic. The results agree with STM data showing the formation of striped disorder and local (2x1) and (3x2) domains at 60 K. DFT calculations yield a degeneracy of the three structures at 0 K. The formation of a long-range ordered state at 300 K out of a low-temperature disordered state seems in apparent contradiction with entropy considerations, but can be rationalised by assuming temperature-dependent interactions in the system. A possible explanation is a Peierls interaction in a surface resonance.