When a zinc oxide (ZnO) nanowire is bent, polarization that is perpendicular to its c-axis (i.e. the longitudinal direction of the nanowire) will be induced due to the piezoelectric effect of ZnO crystal. In this paper, based on the theories of the piezoelectric effect and elasticity, we derive the relation between this polarization and the degree of bending, and calculate the potential of the electric field excited by this polarization. The result is in agreement with that of the experiment [Z.L. Wang, J.H. Song, Science 312 (2006) 242].

Peptide-based self-assembling systems are increasingly attractive because of their wide range of applications in different fields. Peptide nanostructures are flexible with changes in the ambient conditions. Herein, a reversible shape transition between self-assembled dipeptide nanotubes (DPNTs) and vesicle-like structures is observed upon a change in the peptide concentration. SEM, TEM, AFM, and CD spectroscopy were used to follow this transition process. We show that dilution of a peptide-nanotube dispersion solution results in the formation of vesicle-like structures, which can then be reassembled into the nanotubes by concentrating the solution. A theoretical model describing this shape-transition phenomenon is presented to propose ways to engineer assembling molecules in order to devise other systems in which the morphology can be tuned on demand.

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.

The method to obtain phonon dispersion of achiral single-wall carbon nanotubes (SWNTs) from 6 x 6 matrix proposed by Mahan and Jeon(7) has been extended to chiral SWNTs. The number of calculated phonon modes of a chiral SWNT (10, 1) is much larger than that of a zigzag one (10, 0) because the number of atoms in the translational unit cell of chiral SWNT is larger than that of an achiral one even though they have relative similar radius. The possible application of our approach to other models with more phonon potential terms beyond Mahan and Jeon's model is discussed.