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 44.17: Poster

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

Molecular flexibility as a factor affecting the surface ordering of organic adsorbates on metal substrates — •S. Soubatch, R. Temirov, and F. S. Tautz — International University Bremen (Jacobs University Bremen as of spring 2007), Bremen, Germany

The effect of molecular flexibility on the surface ordering of complex organic adsorbates is explored by mean of LEED and STM, using DH4T and mixed DH4T-tetracene phases on Ag(111) as model systems. Above 273 K, DH4T forms a nematic liquid crystalline phase. At 273 K, a reversible phase transition to a long-range ordered, point-on-line coincident phase is observed. However, this ordered state is still affected substantially by the flexible nature of DH4T, which materializes in a large number of local structural defects. If traces of DH4T are co-evaporated with tetracene, inclusions of a 1:1 stoichiometric DH4T-tetracene phase are found in a tetracene/Ag(111) matrix. In this mixed phase, tetracene and the two surface enantiomers of DH4T arrange in a complex stripe structure. The mixed phase shows a higher degree of order than present at the pure DH4T/Ag(111) interface, which also lacks chiral organization. The addition of tetracene molecules as structural templates stabilizes certain conformations of DH4T and thus, by balancing its structural flexibility, allows the surface-induced chirality of DH4T to become a decisive factor in determining the structure of the mixed phase.