Atomic Force Microscope Grain Size Analysis and Surface Shearing Effects on PVDF(Tr-FE) Ferroelectric Surface
Jiménez Tejeda, Kety M.
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The effects of applying a shearing force on copolymer of Polyvinylidene Fluoride with Trifluoroethylene (P(VDF-TrFE) thin film has been studied. A shearing technique was used to induce stress on the film, which may produce self-assembly effects on the polymer and also changes in the grain size. Six samples were fabricated from silicon oxide substrates with Langmuir Blodgett vertical deposition techniques, at 200 monolayers each, with a final thickness between 20-60 nm. The content ratio of the P(VDF-TrFE) co-polymer was 75:25 with Curie of 119 ºC and melting point of 153 ºC. After deposition, five samples were annealed in a vacuum during 24 hours at temperature of 130 ºC. Before shearing, the samples were annealed for a second time at 130 ºC for 15 minutes. Throughout the shearing process, the multilayer thin film of the PVDF copolymer was submitted to shear stress of the order of magnitude of 104 Pa for 30 minutes; the tension force was different for every sample. Contact mode AFM images of the samples before and after shearing process were taken and analyzed with a Scanning Probe Image Processor (SPIP) Analyzer, with which we could obtained the grain size distribution and mean grain size of the samples. Data revealed significant change in grain size after the shearing process. The molecular structure packing and the ferroelectric phase of the multilayer thin film was verified by a Rigaku X ray diffractometry before and after the shearing process, showing that the pressure and tension used during shearing was not enough to produce a phase change of the polymer.