Multimodal Microscopy of Partially Oriented para-Hexaphenylene Nanoaggregates

Organic molecular beam deposition (OMBD) of para-hexaphenylene (p6P) on polycrystalline platinum results in the formation of unique nanoaggregates, predominantly as nanofibers and nanoribbons. These aggregates exhibit distinct morphological properties, as revealed by atomic force microscopy (AFM). Grazing incidence X-ray diffraction (GIXD) confirms the p6P herringbone structure as partially oriented aggregates with a bias of previously observed contact planes parallel to the substrate. The optical properties of the aggregates are analyzed using polarization microscopy, fluorescence microscopy, and Raman microscopy to distinguish three different aggregate types with a focus on aspects such as molecule orientation within the aggregates, including those lying and standing upright. Polarized microscopy indicates that the molecular orientation within the fluorescing, fiber-like aggregates is generally perpendicular to the long fiber axis and parallel to the substrate, which seems not to be the case for the other two types. This finding is crucial for applications utilizing p6P's polarized emission, such as in photonic and optoelectronic devices.