Electrical Transport Properties Of Hexagonal WO₃ Nanowires Modulated By Argon Ion Beam Etching And Hydrogen Ion Doping

The memristor not only has the superiorities of low power consumption,fast rewritable speed,simple structure and compatibility with CMOS process,but also functions such as non-volatile state logic operation,brain-like neuromorphic calculation,and high-density information storage,etc.However,the unclear microscopic mechanisms of ion-electron couple transport lead to unstable performance of the memristive devices.Therefore,improving device performance and the in-depth study on the resistive witching mechanism of memristors at the nanoscale is very critical for its widespread application.In this paper,the selected hexagonal WO₃ nanowire has a unique tunnel structure in the c direction,is very convenient for electrons or other ions to transport in the lattice under the force of external electric field.More importantly,WO₃has distinctive electronic band structure,which provides a prerequisite for hydrogen ion-electron double injection and its coupled transport.Besides,argon ion beam etching is applied to improve the electronic transport performance of the memristive devices greatly.The main research contents and results of this thesis are listed as follows:1.Hexagonal WO₃ nanowires with good dispersibility and crystallinity were prepared by simple hydrothermal method,and then SEM,TEM,XRD,Ramam and other basic characterizations were carried out.Some high-quality devices like Au/h-WO₃ nanowire/Au were fabricated by the standard photolithography and electron beam exposure technique successfully.2.After being etched by the argon ion beam,XPS,XRD,TOPAS fitting,Ramam,and optical absorption spectroscopy were performed systematically.The results indicate that the concentration of oxygen vacancy increases with the etching time.At the same time,the lattice constants a,c,the interplanar spacing d,the band gap,etc.are all decreased to some extent.Besides,the I-V characteristic curves were recorded after etching,which shows that the concentration of oxygen vacancy increases with the etching time.And the electrical transport performance is enhanced prominently and the oxygen vacancy levels are doped shallowly in the band gap.3.The current-voltage characteristics and resistive switching mechanisms,based on the two-terminal Au/hexagonal WO₃ nanowire/Au devices,have been investigated under different relative humidity levels.Under high relative humidity,the hydrogen ions produced by hole-oxidizing adsorbed water molecules will drift to the negatively biased electrode in the adsorbed water layer based on Grotthuss mechanism,and accumulate near the negatively biased electrode,which will deplete the itinerant electrons and increase the height of the Schottky barrier prominently.The electrical transport properties are dominated by the electrode-limited conduction mechanism?Schottky emission?.Once the bias voltage is larger than a critical value,these accumulated hydrogen ions are reduced to hydrogen immediately by the hot electrons injected from the negatively biased electrode,and then the electrical transport properties are dominated by the bulk-limited conduction mechanism?Poole-Frankel emission?.The generation and accumulation of hydrogen ions induced by bias voltage endows the device based on hexagonal WO₃nanowire with more abundant resistive switching properties.