Template-based,near-ambient synthesis of crystalline metal-oxide nanotubes,nanowires and coaxial nanotubes

In response to a growing need for metal-oxide nanotubes and nanowires for nanoelectronic applications and size-effect studies, crystalline nanotubes and nanowires in a range of metal oxides have been synthesized at near-ambient conditions and without the application of heat treatments, pressure or an external electric field. Specifically, the mechanisms of formation of crystalline TiO₂ nanotubes and nanowires from flourine-based liquid precursors inside anodic aluminum oxide templates have been elucidated. This method can be extended to synthesizing nanotubes/nanowires of other crystalline metal oxides, such as ZrO₂, SnO₂ and FeOOH. Using sequential deposition, TiO₂/ZrO₂ coaxial nanotubes have been synthesized. In principle, the methods outlined here could be used to fabricate crystalline nanotubes and nanowires of tailored dimensions in other metal oxides. The ability to synthesize, at near-ambient conditions, crystalline metal-oxide nanotubes and nanowires of tailored geometries represents a clear advantage in terms of minimal equipment requirements, low cost and possible incorporation of biomolecules and temperature-sensitive moieties.