Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 30: Focussed session: Functional molecules at surfaces I
O 30.9: Talk
Tuesday, March 27, 2012, 13:00–13:15, A 053
Molecular orientation of tetracene in ordered and disordered layers on Ag(111) — •Tomoki Sueyoshi1, Martin Willenbockel1, Michael Naboka2, Alexei Nefedov2, Sergey Soubatch1, Christof Wöll2, and Stefan Tautz1 — 1Peter Grünberg Institut (PGI-3), JARA, Forschungszentrum Jülich, Germany — 2Institute of Functional Interfaces, Karlsruhe Institute of Technology (KIT), Germany
Tetracene on Ag(111) forms different structural phases depending on preparation condition. Based on scanning tunneling microscopic/spectroscopic studies, we indicated that variation of the tilt angle of tetracene molecule (and local molecular environment) results in different electronic properties of tetracene layers. This demonstrates how it is important to know the molecular orientation in the layer to understand the electronic structure of molecular layers. Here, we investigates tetracene molecular orientation in ordered and disordered layers on Ag(111) using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Quantitative analysis of NEXAFS intensity reveals that monolayer alpha-phase consists of flat-lying molecule with a tilt angle of less than 10 degrees whereas complex bi-layer beta-phase includes tilted molecule with an average tilt angle of 36 degrees. At room temperature the monolayer alpha-phase gets disordered and the average tilt angle of tetracene molecules changes to 15 degrees, accordingly. The increase in the tetracene tilt angle suggests that an order-disorder transition of tetracene monolayer is achieved by getting additional degree of freedom for tetracene to move.