The stress-dependent piezoelectric coefficient of ZnO wire measured by piezoresponse force microscopy

We studied a converse piezoelectric effect of individual ZnO wires by using a conductive cantilever tip attached to the end of each wire. The piezoelectric coefficients d 33 of individual wires were measured and found to be in the range of 1–45 pm V −1 , some of them being much larger than that of bulk ZnO. A 20% increment of d 33 was found when 0.32 GPa stress was applied, but the d 33 was decreased when the wire was bent by excessive compression.