Research On The Interaction Between Ferroelectric Polymer And SWNTs

Poly(vinylidene difluoride) (PVDF) has some excellent properties like insulation, transparency, chemical stability, radiation resistance, and mechanical strength. Especially, when it is in β-phase configuration, outstanding ferroelectric property is exhibited. However, the most common and stable configuration is the α-phase, so in general, the β-phase is difficultly obtained by drawing films, by applying a high electric field, by synthesizing copolymer, or by crystallizing directly from the melt, which remain the obstacle to the application of PVDF. Nowadays, people found that the introduction of some single-walled carbon nanotubes (SWNTs) would lead the PVDF matrix to crystallize into the β-phase. Furthermore, the composite has high dielectric constant, and has potential in a wide range of fields, such as ferroelectric memories, transducers, supercapacitors, and flexible transistors.However, people are not clear with the interaction between PVDF and SWNT yet, and obvious leakage current is detected when the composite is used as the gate insulator of a transistor. In our work, the interaction between these two materials, and their conduction and leakage mechanisms in electric devices are investigated.PVDF solution and membrane blending with well-dispersed SWNTs have been prepared with efforts, in order to investigate the composite.Because of the interaction, SWNTs are observed to form a homogeneous dispersion in the fluoropolymer matrix. Raman measurements showed sizable changes in the frequencies and intensities of SWNTs and PVDF in the composites compared with the values in pristine SWNTs and neat PVDF. This originates from the polymer’s preferable interaction with metallic SWNTs (m-SWNTs), especially with small-diameter tubes, due to non-vanishing Fermi electrons and increased curvature-induced strain energy. In addition, the selective dispersion of m-SWNTs induced remarkable enhancement in the β ferroelectric phase of PVDF, as demonstrated in Fourier transform infrared spectroscopy (FTIR), and piezoelectric force microscopy (PFM).The thin film transistors with PVDF/SWNT channel layer was fabricated, and the output characteristics were tested to discuss the leakage and conduction mechanisms. To explain the tunneling leakage current at the interface of Au/PVDF, and the influence of SWNTs, the energy band diagrams are introduced. Because the current between source and drain electrodes can be controlled by the gate voltage, our hypothesis turns out to be true. Furthermore, according to the Ⅰ-Ⅴ characteristics, the space charge limited current (SCLC) model is set up, and fitted with the experimental data to discuss the conduction mechanism.