Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 36: Posters: Bio/organic Molecules on Surfaces, Graphene, Solid/liquid interfaces, Metal Substrates, Electronic Structure Theory
O 36.14: Poster
Dienstag, 1. April 2014, 18:30–22:00, P1
Spontaneous change in molecular orientation at order-disorder transition of tetracene on Ag(111) — •Tomoki Sueyoshi1, Martin Willenbockel1, Michael Naboka2, Alexei Nefedov2, Serguei 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
Molecular orientation is not only correlated closely to the electronic properties of molecular layers but also related directly to formation of various molecular phases composed of the identical molecule(s). Here, we investigate the molecular orientation of tetracene in ordered and disordered layers on Ag(111) using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy [1]. Quantitative analysis of NEXAFS intensities reveals that the compact monolayer α −phase at 150 K consists of essentially flat-lying molecules with an average tilt angle α < 9∘ with respect to the Ag(111) surface. At room temperature the tetracene monolayer is dynamically disordered with α = 15 ± 4∘ (α ′−phase). The increase in the average tetracene tilt angle indicates that orientational degrees of freedom perpendicular to the surface drive the order-disorder transition in the tetracene monolayer on Ag(111). We argue that the phase transition can be explained by a delicate balance between the interfacial enthalpy and the orientational entropy.
[1] T. Sueyoshi, M. Willenbockel, M. Naboka, A. Nefedov, S. Soubatch, C. Wöll, and F. S. Tautz, J. Phys. Chem. C 117, 9212 (2013).