Synthesis, characterization and electronic properties of electrospun PZT and carbon nanofibers.

摘要

One-dimensional (1D) nanostructures are the smallest dimension structures for efficient transport of electrons and optical excitations, and can be used as building blocks in bottom-up assembly in diverse applications in nano-electronics and photonics. Lead zirconate titanate (PZT) and carbon nanofibers are two typical and challenging examples of 1D nanostructure. However, the former has not been synthesized and the later has been synthesized only in a limited number of costly ways. They were synthesized using recently “rediscovered” electrostatic generation, i.e. electrospinning, technique, combined with metallo-organic decomposition (MOD) and vacuum heat treatment techniques, and characterized using x-ray diffraction, Raman microspectrometer, Fourier-transform infrared spectrometer, scanning electron microscopes equipped with energy dispersion spectrometer, Auger electron spectroscope, and scanning probe microscope (SPM). It was found that both of the synthesized PZT and carbon fibers have diameters on the order of 100 nm. Furthermore, carbon nanofibers have d₀₀₂ = 0.371 nm, stack size L_c = 1.651 nm and in-plane graphitic crystallite size L_a between 1.5 and 2.6 nm.; Piezoresponse imaging technique was transplanted to visualize polarization domains within PZT fibers. It was revealed that the grain size is around 1 μm, and domain sizes range from 100 to 500 nm. To validate the experimental effort, the electrostatic interaction between the SPM tip and the fiber was simulated using finite element method. It was found that the cone shape of the tip controls the electric field immediately below the tip and that the field is more concentrated in PZT fibers than in thin film.; Then electron transport properties of carbon nanofibers were investigated. Conductivity of a synthesized carbon nanofiber was measured between 1.9K and 300K exposed to zero magnetic fields, and in the presence of a magnetic field between −9 and 9T at room temperature, 10, 3.5 and 1.9K, respectively. It was found that the positive magnetoresistance at room temperature has a parabolic relation with the magnetic field, from which carrier mobility μ _H = (4.25 ± 0.01) × 10−3m2 /Vs and concentration n = (2.02 ± 0.04) × 1025 m−3 were obtained.; The fiber manifested large negative magnetoresistance at low temperature, with the maximum (−75%) found at 1.9K and 9T. Temperature and magnetic field dependence of the magnetoresistance was explained and modeled using the 2D weak localization effect. GB,T =G∞+e2 ph 32Y1 2+ B2B -Y 12+ B1B - 12Y1 2+B 3B Temperature dependence of the zero magnetic field conductivity was modeled using a modified simple two-band model with temperature dependent mobility, and a correction predicted by 2D weak localization model. sT=s 0+c1lnT+cTT u<