The method depends on screw dislocation, defects that help in the creation of spiral steps on an otherwise flawless crystal face. When atoms land on the crystal surface, they form spiral ramps; in harnessing the defect to make nanostructures, atoms collect on the surface of a dislocation spiral, and the strain associated with screw dislocations builds up in the tiny structures they create.

Published in Science [Morin et al., Science (2010), doi: 10.1126/science.1182977], the study found that a simple crystal defect, a screw dislocation, drives the growth of hollow zinc oxide nanotubes that are just a few millionths of a centimeter thick. Led by Song Jin of the University of Wisconsin-Madison, the research initially developed from a study of how nanowire growth can be driven by screw dislocations, and how such growth also occurs for other nanowire materials grown in solution.

There are two main element of the research. The first is an understanding of the spontaneous formation and growth of single-crystal inorganic nanotubes. The team explored why thick-walled nanotubes can have very little Eshelby twist due to the competition between hollow dislocation cores, and Eshelby twist in relieving the dislocation strain energy. The second element was showing that the dislocation-driven growth of nanowires or nanotubes can be rationally designed through an understanding of crystal growth theories and the concept of dislocation-driven nanomaterial growth.

The study also compared the prediction from the classical crystal growth theory on dislocation-driven and layer-by-layer growth with the growth kinetics observed under carefully controlled low supersaturation conditions. This confirmed that the anisotropic crystal growth of these 1D nanomaterials is indeed driven by screw dislocations.

The work provides a theoretical framework for controlling solution nanowire/nanotube growth that can be applicable to many other materials apart from zinc oxide. Once refined, this new understanding could eventually be applied to the large-scale, low-cost solution growth for rational catalyst-free synthesis of 1D nanomaterials.

These have many potential applications in electronics, solar power, battery and laser technology, as well as chemical and biological sensing. In renewable energy, for example, a large amount of such materials could be used to convert sunlight to electricity, and they could also provide new raw materials for battery electrodes and thermoelectric devices.