SiO(2)/Ta(2)O(5) core-shell nanowires and nanotubes.

One-dimensional nanostructures such as nanowires, nanobelts, and nanotubes have attracted much attention as a result of their unique properties, which can be applied in the fabrication of biomedical sensors, optoelectronic devices, field-effect transistors, and field-emission devices, for example. In particular, one-dimensional nanostructures of metal oxides such as ZnO, SnO2, [3] a-Fe2O3, [4] WO3, [5] and Ta2O5, [6] so-called functional materials, have been widely studied. The synthesis of these functional metal oxide nanostructures are investigated widely through physical and chemical reactions, including vapor–liquid–solid (VLS), solution–liquid–solid (SLS), vapor–solid (VS), and other template-based approaches. Ta2O5 is a fascinating functional material that has been used in applications such as dynamic random access memory (DRAM) devices, antireflection coating layers, gas sensors, photocatalysts, and capacitors owing to its high dielectric constant, high refractive index, chemical stability, and hightemperature piezoelectric properties. 11] However, the synthesis of Ta2O5 nanostructures (e.g. nanowires or nanotubes) has had little success as a result of its high melting point. On the other hand, silica (SiO2) nanowires are well developed for electronic and optoelectronic applications. Various methods of synthesizing SiO2 nanowires include pulsed laser ablation, directed growth from a silica substrate or silica nanoparticles in a reductive atmosphere, direct growth from a Si substrate with catalyst, carbon-assisted and carbothermal reduction of silicon dioxide or metal oxides, and the sol–gel method. All of these approaches are direct, simple, and high-yielding, which are important factors for commercial applications.