Figure 2.

(a) threshold-like, (b) self-rectifying bipolar, and (c) ordinary bipolar I–V characteristics of a ZnO nanoisland at different current compliance. The nanoisland firstly underwent process (0) as indicated in (a), i.e., a voltage sweep from 0 to 10 V under a current compliance of 5 nA. Then the nanoisland underwent four voltage sweep processes sequentially (process (1): 5 to 0 V; process (2): 0 to −5 V; process (3): −5 to 0 V; process (4): 0 to 5 V) as illustrated in (a). Under the current compliance of 10 nA, 100 nA–10 μA, and 100 μA–1 mA, the voltage sweep processes resulted in three types of resistive switching (threshold-like, self-rectifying bipolar and ordinary bipolar) in (a), (b) and (c), respectively.