Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)

O 44.7: Poster

Mittwoch, 28. März 2007, 17:00–19:30, Poster C

SPA-LEED and NIXSW investigations of PTCDA on Ag(100) — •Julian Ikonomov¹, Oliver Bauer¹, Serguei Soubatch², Adam Lassise², Stefan Tautz², and Moritz Sokolowski¹ — ¹Institut für Physikalische und Theoretische Chemie der Universität Bonn, Wegelerstr. 12, 53115 Bonn, Germany — ²International University Bremen, School of Engineering and Science, P.O. Box 750 561, 28725 Bremen, Germany

We report studies of vacuum deposited PTCDA films on Ag(100). The SPA-LEED (Spot Profile Analysis Low Energy Electron Diffraction) measurements show two ordered structures on Ag(100). Up to one monolayer coverage, PTCDA forms a commensurate c(4 × 4) structure with two molecules, perpendicularly oriented to each other in the unit cell. The ordered structure is stable up to a sample temperature of 690 K, at which a phase transition to a disordered phase occurs. Cooling the sample back to room temperature recovers the ordered structure. At a coverage above one monolayer the second layer orders in a different structure on top of the c(4 × 4)-ordered first layer. Herein the molecules are arranged in a herring-bone pattern, and the unit cell is very similar to that of the (102) plane of the PTCDA bulk crystal. NIXSW (Normal Incidence X-Ray Standing Wave) experiments were performed on the monolayer in order to determine the vertical adsorption height and to compare it with values determined earlier for PTCDA on Ag(111) [1]. Supported by SFB 624.

[1] A. Hauschild et al., Physical Review Letters 94 (2005) 036106.