Synthesis,Characterization And Electrical Transport Properties Of Sodium Tungsten Bronze Nanowires

The hexagonal sodium tungsten bronze?h-Na_xWO₃?nanowire has a unique structure of one-dimensional tunnel,and the sodium ions in the tunnel can migrate along the nanowire under the electric field induced by bias voltage,which endows the nanowires with excellent resistive switching behavior.Research on electron-ion coupled transport behavior in nanowires benefits the understanding on resistive switching mechanism of metal oxide.Then,the resistive random access memory prototype device with good stability,high repeatability and strong controllability can be fabricated based on Na_xWO₃ nanowires.The main experimental results are summarized as follows:1.Highly crystalline h-Na_xWO₃ nanowires,with diameters of100-400 nm and lengths of 7-10?m,have been synthesized successfully by hydrothermal method.Then,the characterizations of nanowires by X-ray diffraction,transmission electron microscope and X-ray photoelectron spectroscopy demonstrate that as-synthesized nanowires are sodium tungsten bronze nanowires grown along c axis.2.The Au/h-Na_xWO₃ nanowire/Au devices.with asymmetric contact barriers were fabricated based on individual nanowire by using photolithography technique.It is demonstrated directly by energy dispersive spectroscopy that sodium ions can be driven to transport along the nanowire under the electric field induced by bias voltage.3.The Au/h-Na_xWO₃ nanowire/Au device exhibits different resistive switching behaviors under small and large bias voltage.The drift of sodium ions might induce distinct changes in its concentrations near the junctions between Na_xWO₃ nanowire and Au electrodes under a relatively large bias voltage,which will change the heights of these two Schottky barriers and switch this device to high or low resistance state accordingly.The drift of sodium ions also might induce strong disorder in its distribution,which will lead to the localization of states in the conduction band tail.The localized states can be filled or drained under a relatively small bias voltage,which will also switch the device to high or low resistance state.4.The surface potential distribution of Na_xWO₃ nanowire is observed directly by Kelvin probe force microscopy?KPFM?,and it is inhomogeneous along nanowire.We also use KPFM,electrostatic force microscopy and scanning microwave impedance microscopy to study the electrical properties of two dimension NbS₂/BN heterostructure grown by chemical vapor deposition and exfoliated MoS₂.