Size dependence of transverse electric transport in single ZnO nanoneedles

We report a size dependence of transverse electric transport in single ZnO nanoneedles with diameters ranging from 5 to 50 nm. Under the same voltages, the measured transverse current through the single ZnO nanoneedle was found to decrease dramatically with the decreasing diameters from 50 to 20 nm, and no current were detected when the diameters are smaller than 20 nm. A spherical electric transport model is proposed to explore the origin of the size dependence.