Single-Crystal-like Structure of Poly(9,9-dioctylfluorene) Thin Films Evaluated by Synchrotron-Sourced Grazing-Incidence X-ray Diffraction

Detailed structures of friction-transferred poly(9,9-dioctylfluorene) (PFO) thin films have been studied using synchrotron-sourced grazing-incidence X-ray diffraction (GIXD). The results of in-plane GIXD were in full agreement with those of electron diffraction in our previous study. We also revealed the structures of liquid-crystalline (LC) and crystalline films that were prepared by rapid and slow cooling from the LC melted state of the friction-transferred films, respectively. For the crystalline films, the results of in-plane GIXD were not in full agreement with those of electron diffraction; additional weak peaks of the odd 00l reflections were observed only in the GIXD profiles. This implies that the twofold screw symmetry along the c-axis of PFO is broken. The rocking profiles for each reflection gave the order parameter of almost one for the crystalline films and 0.67 for the LC films. These results suggest the ability of friction transfer for obtaining single-crystal-like thin films and the importance of carefully designed annealing process for the applications of the films to various optoelectronic devices.