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Nanomaterials, such as films, nanowires, nanotubes, nanofibes, have surface effect,size effect,macroscopic quantum tunneling effect and quantum confinement effect, which are obviously differentfrom macroscopic materials. So, nanomaterials show some excellent optical, electrical, magnetic,mechanical properities. BiFeO3, with Curie temperature about850℃, Neil temperature about370℃, isthe multiferroic materials which have the ferroelectricity and magnetism. Via the magnetoelectric effectin the BiFeO3, we can use electric field to control magnetic field or to induce ferromagnetic phasetransition and in the contrast, electric field and ferroelectric phase transition can be controled bymagnetic field. Simultaneously, BiFeO3nanomaterials are nanomaterials and multiferroic materials, sothere must be some special properities. Recent studies demonstrated the BiFeO3films have spontaneouspolarization enhancement, switchable ferroelectric diode effects, photovoltaic effects, piezoelectric andTHz radiation properties. Glinchuk had predicted the giant magnetoelectric effect in nanowires, and in2012, K.Prashanthi had proved this effect in polycrystalline BiFeO3nanowires.Recently, Liu hadsynthesized the single-phase BiFeO3nanowires use hydrothermal method. In the ferroelectric nanowires,some reports had showed the multi-domain structure in PZT nanowires and single domain structure inBaTiO3nanowires.Based on the above consideration, we attempted to synthesize pure phase, single-crystal and evenlydispersed BiFeO3nanowire in this paper, then tested on the AFM which equips with PFM mode to revealthe domain structure. After the PFM test, a longitudinal voltage was applied on the nanowire toinvestigate the ferroelectric switching of OP （out-of plane） polarization. Specific work are in following three parts:1The synthesis of single-crystal BiFeO3nanowire with different solventsSingle-crystal BiFeO3nanowires are attempted to synthesized by hydrothermal method fromBi（NO3）3·5H2O and FeCl3·6H2O. The results showed that there are not BiFeO3nanowires with ethyleneglycol as a solvent, but when we choose the acetone as solvent, the product is single-crystal BiFeO3nanowires, and SEM and TEM image showed the nanowire with length of5-10um, diameter of50-150nm.2The ferroelectric domain structure in BiFeO3nanowiresUsing PFM mode in atomic force microscope, the domian structure on BiFeO3nanowire are testedand the OP images showed that the structure are stripes along the axial direction of the nanowire, whichrepresent different polarization orientations. After the signal analysis of nanowire and silicon substrate,we found that the signal on nanowire is proportional to the AC bias, the inverse piezoelectric effect, andthe signal on silicon substrate is proportional to square of the AC bias, the dielectric electrostrictiveeffect.3The OP ferroelectric polarization switching on BiFeO3nanowireWith a longitudinal voltage applied to BiFeO3nanowire, we observed the OP ferroelectricpolarization switching on nanowire. the OP images showed that there are obvious polariation switching.In some area, the polarization vector is along the electric direction which is normal switching; and inother area, the polarization vector is against the electric direction which is obnormal switching. Afterremoving this DC voltage, the polarization returned to its original orientation, certificated the highlystable and not retentive domains.
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