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 18.64: Poster
Montag, 25. Februar 2008, 18:30–19:30, Poster F
Surface- induced handedness in adsorbed layers — •Philipp Schmidt-Weber1, Thorsten Kampen1, Arantzazu Mascaraque2, Rocio Cortez2, Jan-Hugo Dil1, and Karsten Horn1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin — 2Universidad Autonoma de Madrid, Spain
Molecules that are achiral in the gas phase may acquire a chiral character through the loss of symmetry elements, which has a strong influence on their arrangement in long-range ordered structures. We have studied stilbene and its derivates, using STM, LEED and photoemission with the aim of identifying such ordering processes. Dicarboxy-stilbene (DCSB) loses its carboxyl hydrogen atom when adsorbed on Cu(110), and acquires a handedness on the surfaces which is readily seen in STM images. The two enantiomers then arrange in different long-range ordered structures ("herringbone" and "parquet" patterns), which themselves possess a handedness, i.e. they exist in a dextro- and laevo- form. Using STM images in which both the substrate and the adsorbate are imaged with atomic resolution, we were able to identify two distinct types of adsorption sites as basic building blocks of the long-range structures. One of these (the "parquet" pattern) is enantiomerically pure, while the other ("herringbone") is a racemic structure. The fact that the latter is the thermodynamically stable one can be understood from general thermodynamic principles.