Deformation-free single-crystal nanohelixes of polar nanowires

Ultrasmall, deformation-free, single-crystal nanohelixes/nanosprings of piezoelectric ZnO are reported. The nanohelixes are made of similar to12 nm nanowires and have a uniform mean diameter of similar to30 nm. The growth follows a hexagonal screw-coiling model, in which the growth of the nanowire is led by the Zn-terminated (0001) front surface due to self-catalysis. A sequential and periodic 60degrees rotation in growth direction among the six equivalent directions of (0111) in an ordered and equally spaced distance results in the formation of the nanohelix. The sequential change in growth direction is to reduce the electrostatic interaction energy caused by the +/-{01 (1) over bar1} polar surfaces of the nanowire, analogous to the charge model of an RNA molecule.