Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)
O 17.20: Poster
Montag, 26. März 2007, 17:30–20:30, Poster C
Optical anisotropy in a self-assembled molecular film — •Thorsten Kampen1, Simona Silaghi2, Philipp Martin Schmidt1, Rocio Cortes3, Arantzazu Mascaraque3, Norbert Esser2, and Karsten Horn1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany — 2Institute for Analytical Sciences, Berlin, Germany — 3Depto. Física de Materiales, Universidad Complutense de Madrid, Madrid, Spain
Among the class of molecules which may be used as molecular switches, stilbene and its derivatives are promising candidates. Here, we present a study on the optical properties of self-assembled 4,4’-stilbene dicarboxylic acid (DCSB) layers on Cu(110). Photoemission spectra show the deprotonation of both carboxylic end-groups upon adsorption resulting in a chemical bonding of the molecule to surface. Scanning tunnelling microscopy images reveal that nucleation of the first molecular layer starts on top of the Cu step edges. The molecular growth proceeds from the stabilized steps into the terraces and two different chiral phases are observed: a metastable enantiomorphically pure phase and a thermodynamically preferred "racemic mixture". The derived surface dielectric anisotropy from the RAS spectra show features assigned to the Cu surface state which vanish for coverages above 1ML. Even for submonolayer coverages spectral features above 3eV are observed and are assigned to optical transitions in DCSB. Specifically, the HOMO-LUMO transition dipole moment which is oriented along the long symmetry axis of the molecule is almost oriented parallel to the [110] substrate direction. This is supported by STM.