Piezoelectric-effect-induced formation of nanorings, nanohelices, and straight nanobelts of ZnO

Piezoelectric effect makes the nanobelt of polar-surface-dominated ZnO single crystal able to decrease its spontaneous polarization through bending. In this article we show that the competition between the electrostatic energy and the elastic bending energy introduces a spontaneous curvature to the ZnO nanobelt and thus results in the formation of nanorings, nanohelices, and straight nanobelts, which were observed in the experiment. The radii of the nanorings and nanohelices are proved to be proportional to their thickness, which is in agreement with the experiment data. The various values of the pitch angle of the helices and their different chiralities are discussed. The properties of such nanorings and nano-helices and their possible applications in nanodevices are also discussed.