Nanoscale investigation of polarization interaction and polarization switching in ferroelectric P(VDF-TrFE) copolymer samples

Ferroelectric properties of thin films and self-assembly of copolymers of polyvinylidene fluoride with trifluoroethylene (P(VDF-TrFE) have been studied. All samples were fabricated with Langmuir-Blodgett (LB) film deposition technique. Two main observations are presented in this dissertation. One is a polarization interaction effect in multi-layered thin films made of two different copolymers, and the other is local polarization switching of the self-assembly, called nanomesas. The multilayer films were built with two different content ratio of P(VDF-TrFE) copolymers. They were P(VDF-TrFE 80:20) and P(VDF-TrFE 50:50) with phase transition temperatures of 133 ± 4°C and 70 ± 4°C respectively. The polarization interaction effect resulted in transition temperature changes of the materials, and the determined interaction length was approximately 11 nm, perpendicular to the film plane. Nanomesas of P(VDF-TrFE) copolymer were found during annealing study of thinner films with less than 3 deposited layer thin films. Nanomesas are disk shaped isolated islands approximately 9 nm in height and 100 nm in diameter in average. Ferroelectric switching properties of nanomesas have been shown macroscopically in the previous studies. In this work, the switching properties of individual nanomesas were probed at nanoscale. Nanomesas, switched with ± 7 Vdc were recorded using piezoresponse force microscopy (PFM). Switching hysteresis loops from a local area of 12∼15 nm 2 within an individual nanomesa were also obtained using switching spectroscopy PFM (SS-PFM). The coercive field determined from the well behaved switching loops is ∼250 ∼ 450 MV/cm