Effect of Substrate Temperature on Molecular Orientation in Evaporated Thin Films of Vinylidene Fluoride Oligomer

A newly synthesized vinylidene fluoride oligomer (OVDF), for which ferroelectric properties are expected when the electric dipoles with the molecules are all aligned, was employed as a prospective evaporation material. Particularly, the crystal structure and molecular orientation in evaporated thin films were examined by a total reflection X-ray diffractometer and reflection absorption infrared spectroscopy. Consequently, it was revealed that the crystal structure of the evaporated films was similar to the form II crystals of poly(vinylidene fluoride) which is a polymeric sample of OVDF, and that the molecular orientations are perpendicular to the substrate. Moreover, it was observed that the molecular orientation changed from perpendicular to parallel to the substrate at the substrate temperature between -30 and -50° C and the stable crystal structure was form II.