SKM 2023 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 15: Optical Analysis of Thin Films II

DS 15.5: Vortrag

Donnerstag, 30. März 2023, 12:30–12:45, SCH A 316

Identification of different polymorphs of a zone-cast perylene diimide derivative with low-frequency Raman and infrared scanning near-field microscopy — •Nadine von Coelln, Christian Huck, Niklas Herrmann, Petra Tegeder, and Jana Zaumseil — Institute of Physical Chemistry, Heidelberg University, Germany

Small-molecule organic semiconductors are prone to form multiple thin film polymorphs. As their charge transport characteristics may vary substantially, effective and fast polymorph characterization techniques are necessary. Here, zone-cast films of perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) were studied with X-ray diffraction (XRD), confocal low-frequency Raman microscopy and infrared scanning near-field microscopy (IR-SNOM). Based on low-frequency Raman spectra and XRD, two different thin film polymorphs of PDIF-CN2 were identified, which form depending on the solvents used for deposition. While confocal Raman microscopy is limited in the spatial resolution of areas, the near-field infrared technique (IR-SNOM) offers the unique possibility of both infrared microscopy and spectroscopy with a spatial resolution down to ∼10 nm. We demonstrate that it is possible to discriminate between neighboring crystalline regions of the two PDIF-CN2 polymorphs by means of IR-SNOM using slight differences in IR absorption. As a non-destructive technique, IR-SNOM may even enable in-situ investigations of thin semiconducting films in functional devices.