Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 7: Metal substrates: Adsorption of organic / bio molecules I

O 7.2: Talk

Monday, March 26, 2012, 10:45–11:00, A 053

Observing Structural Phase Dynamics and Molecular Aggregation in Real Time: Dispersive NEXAFS Applied to Organic Films — •Markus Scholz^{1, 2}, Christoph Sauer^{1, 2}, Michael Wießner^{1, 2}, Holger Wetzstein^{1, 2}, Achim Schöll^{1, 2}, and Friedrich Reinert^{1, 2} — ¹Physikalisches Institut, Experimentelle Physik VII und Wilhelm Conrad Röntgen Research Center for Complex Material Systems (RCCM), Universität Würzburg, D-97074 Würzburg — ²Gemeinschaftslabor für Nanoanalytik, Karlsruher Institut für Technologie KIT, D-76021 Karlsruhe

We present a novel experimental approach which allows following structural and electronic changes in organic films by quick near edge X-ray absorption fine-structure spectroscopy (QNEXAFS). This technique utilizes the energy-dispersive mode of the BESSY UE52-PGM beamline and allows NEXAFS with about one second time resolution. We show the potential of the method on the example of thin films of the organic molecule 1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride (NTCDA). The time-evolution of the NEXAFS signal recorded at different temperatures allows distinguishing between different processes that are involved in the reorganization of the film. Moreover, since the technique also monitors spectroscopic details we are able to study the interplay between film morphology, molecular orientation, and intermolecular interaction in real time. In a meta-stable phase we observe aggregated molecules that exhibit coherent coupling. The signature change of the vibronic progression and of the peak width allow us to quantify the coherent length of the electronic excitation.