Mechanism and Kinetics of Spontaneous Nanotube Growth Driven by Screw Dislocations

Nanosynthesis Without a Twist The synthesis of many nanoscale materials occurs under conditions of changing saturation because generation of product decreases the concentration of reactants. Morin et al. (p. 476) used a flow reactor to maintain conditions of low supersaturation during the growth of zinc oxide nanotubes and nanowires. Under these conditions, growth of the tubes was controlled by the release of stress, which prevented the torquing of the crystals along their axis. Since growth at different saturation conditions matched predictions, this looks like a promising method to develop rational and controlled synthesis of nanomaterials at large scale and low cost. Low supersaturated conditions help control the growth of zinc oxide nanowires and nanotubes from defect sites. Single-crystal nanotubes are commonly observed, but their formation is often not understood. We show that nanotube growth can be driven by axial screw dislocations: Self-perpetuating growth spirals enable anisotropic growth, and the dislocation strain energy overcomes the surface energy required for creating a new inner surface forming hollow tubes spontaneously. This was demonstrated through solution-grown zinc oxide nanotubes and nanowires by controlling supersaturation using a flow reactor and confirmed using microstructural characterization. The agreement between experimental growth kinetics and those predicted from fundamental crystal growth theories confirms that the growth of these nanotubes is driven by dislocations.