Orientation of molecules in phenylene oligomer thin films: influence of the substrate temperature

Para-terphenyl, para-quaterphenyl and para-hexaphenyl thin films were obtained by vacuum sublimation on substrates at various temperatures (413K, 300K and 77K). Depending on the substrate temperature two types of oligomer molecule orientation were observed by X-ray diffraction and confirmed by spectroscopic characterizations. This two “types” of preferred orientation represent preferred grown crystallites; within one type obtained at “low temperature” the molecules are oriented parallel to the substrate, the other type is characterized by molecules approximately perpendicular to the substrate surface.