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O: Fachverband Oberflächenphysik
O 55: Focussed Session: Towards a Quantitative Understanding of Complex Adsorption Structures: Surface Science goes Organic I
O 55.10: Vortrag
Mittwoch, 2. April 2014, 18:45–19:00, TRE Phy
The complex polymorphism and thermodynamic behavior of a seemingly simple system: naphthalene on Cu(111) — •Roman Forker1, Julia Peuker1, Matthias Meissner1, Falko Sojka1, Takahiro Ueba2, Takashi Yamada2, Toshiaki Munakata2, and Torsten Fritz1 — 1Friedrich Schiller University, Institute of Solid State Physics, Helmholtzweg 5, 07743 Jena, Germany — 2Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
Naphthalene, C10H8, is the smallest polycyclic aromatic hydrocarbon (PAH). Despite its rather simple, non-chiral chemical structure naphthalene is known to form three different commensurate phases in epitaxial films on Cu(111), including apparently chiral arrangements of molecules in one of them [J. Phys. Chem. C 114, 13334 (2010)]. In an attempt to understand this polymorphism we performed temperature-dependent and surface coverage-dependent in situ low-energy electron diffraction (LEED) measurements revealing an unexpected and extraordinarily complex structural and thermodynamic behavior. At low coverage the molecules form a disordered gas-like phase which is a consequence of effectively repulsive intermolecular interactions. The chiral structure originates from a precursor that exhibits short-range order at intermediate coverage. This precursor undergoes a steady and reversible orientational shift upon variation of coverage or temperature which ultimately yields a long-range ordered stable epitaxial film, thereby resembling a liquid–solid phase transition. At higher coverage a competing point-on-line structure, which has not been reported before, is preferred to the commensurate chiral structure.