The polarization state in VDF/TrFE copolymer thin films studied by scanning probe microscopy

Copolymers of vinylidene fluoride, VDF, and trifluoroethylene, TrFE, are representative ferroelectric polymers. Their local properties, such as domain structure and domain wall motion, are not well known because of its complex structure. In the isothermally crystallized samples, we can obtain lamellae that grow separately on the substrates. Then in order to discuss the local state of the polarization in VDF/TrFE copolymer thin films, we observed piezoelectric response images and surface potential images of the samples by piezoresponse force microscopy, PFM, and Kelvin force microscopy, KFM, respectively. We found that the piezoelectric response and/or surface potential depend on the crystal morphology. For example, piezoelectric response was large for edge-on lamellae, while it was weaker for flat-on lamellae. We also examined the change of these images due to the poling treatment.