Characterization of memristive properties The electrical transport measurements were carried out with a Keithley SourceMeter 2602 (Keithley Instruments Inc., Cleveland, USA) on a variable temperature probe station. In order to eliminate the effect of water absorption, the probe station is placed in a homemade vacuum chamber, which can be vacuumized to a base pressure less than 10−1 Pa by mechanical pump, or filled with dry air or inert gases. Results and discussion Figure 1 shows typical I V curves recorded for an Au/WO3 nanowire/Au device with different bias sweep LXH254 in vivo ranges in the sequence of 0→V max→0→−V

max→0 at room temperature in vacuum. When the bias sweep range is small (less than 1 V), the I V curves is perfectly linear and symmetric, which implies that the contacts between find more the WO3 nanowire and the two Au electrodes are ohmic. At this moment, the electric field strength in the WO3 nanowire is about 106 V/m due to the length of WO3 nanowire between two electrodes which is about 1 μm (upper left inset of Figure 1). As the bias sweep range increases, the I V curve will become nonlinear, and will not superpose itself any longer when bias voltage is swept in different directions. That

is, the device is switched gradually to high resistance state under large positive bias voltage and switched back to low resistance state under negative bias voltage, which has been named as electrical hysteresis or memristive switching [14, 15, 27]. Figure 1 also indicates that the parts under small bias (less than 1 V) in these I V curves are almost linear. However, if the bias voltage is swept in the sequence Quisinostat nmr of 0→−V max→0→V max→0, hysteretic-type resistive switching from the low (high) to the high (low) resistance level

occurs under negative (positive) bias voltage (datum not shown here), instead of under positive (negative) bias voltage as described above. As shown in lower right inset of Figure 1, the linear resistance of the WO3 nanowire is about 20 Cyclin-dependent kinase 3 MΩ, which can be switched remarkably to about 500 MΩ after being excursed under 8 V bias voltage and back to about 20 MΩ after being excursed under −8 V bias voltage. Therefore, two-terminal RRAM can be fabricated based on individual WO3 nanowires, which can be written by a large bias voltage and read by a small bias voltage. Figure 1 Typical I – V curves recorded with different bias sweep ranges. The black, red, and green curves are recorded for an individual WO3 nanowire at room temperature in vacuum with 1, 3, and 5 V, respectively. Inset in the upper left corner is a SEM image of the WO3 nanowire device. Inset in the lower right corner shows the I-V curves recorded within a small sweep range after large positive and negative bias excursion. Inset in the upper right and lower left corner are schematic diagrams showing the movement of positively charged oxygen vacancies.