As the temperature increases, the overall resistance of the WO3 nanowire will decrease

correspondingly, which is consistent with that of a typical semiconductor. On the other hand, the WO3 nanowire will exhibit hysteretic resistance switching though the bias sweep range is this website less than 1 V. The electrical transport properties of WO3 are known to be governed by the hopping conduction mechanism, and the electrons localized at the oxygen vacancies are the major carriers [1]. Theoretical calculations and experimental results indicate that the electrical transport and optical properties of WO3−x films depend on the levels of oxygen vacancies: films with x > 0.2 are metallic and conductive, and those with x < 0.167 are transparent and resistive [17]. The oxygen vacancies act as +2-charged dopants and will drift when the electric field strength is strong enough, which will modulate the concentration

distribution of oxygen vacancies and then the electrical transport properties. At room temperature, when bias voltage less than 1 V is applied to the two electrodes with a separation of 1 μm, the strongest electric field in the WO3 nanowire will be less than 106 V/m, and the drift of oxygen vacancies is negligible. At the moment, WO3 nanowires exhibit resistive characteristics, and the I V curves are perfectly linear and symmetric. The drift of oxygen vacancies can be enhanced evidently by increasing the strength of electric field or the temperature, which will result in DMXAA datasheet a change in the concentration of oxygen vacancies along the axial direction and then the resistance of the WO3 nanowire. The resistance of WO3 nanowire keeps at a minimum value when oxygen vacancies distributes

uniformly along the axial direction. When the bias voltage is swept from 0 to V max (−V max) and then back to 0, the drift why of oxygen vacancies results in departure from the uniform distribution, which will lead to device switching gradually to high resistance state. When the bias voltage is swept subsequently from 0 to −V max (V max) and then back to 0, the drift of oxygen vacancies restores the uniform distribution, which will lead to device switching gradually to low resistance state. Therefore, the critical electric field for oxygen vacancy drifting in WO3 nanowire is one order of magnitude less than that in its granular film [28], which might be attributed to its nanoscale diameter and single crystalline structure. Figure 2 EPZ004777 Log-scale and linear-scale (inset) I – V curves recorded for an individual WO 3 at different temperatures. Another important characteristic of these I-V curves in Figure 2 is an increase in the asymmetry between positive and negative bias voltages with increasing temperature, which might be attributed to the asymmetry in the two ohmic contacts between WO3 nanowire and electrodes. Figure 3a shows the typical I-V curves recorded at different temperature in vacuum for the WO3 nanowire device with obviously asymmetric ohmic contacts.