[show abstract][hide abstract] ABSTRACT: A scalable and versatile method for the large-scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates, including amorphous quartz and fluorinated tin oxide, is reported. The synthesis involves the chemical-vapor transport of metal oxide vapor-phase species using air or oxygen flow over hot filaments onto substrates kept at a distance. The results show that the density of the nanowires can be varied from 10(6)-10(10) cm(-2) by varying the substrate temperature. The diameter of the nanowires ranges from 100-20 nm. The results also show that variations in oxygen flow and substrate temperature affect the nanowire morphology from straight to bundled to branched nanowires. A thermodynamic model is proposed to show that the condensation of WO(2) species primarily accounts for the nucleation and subsequent growth of the nanowires, which supports the hypothesis that the nucleation of nanowires occurs through condensation of suboxide WO(2) vapor-phase species. This is in contrast to the expected WO(3) vapor-phase species condensation into WO(3) solid phase for nanoparticle formation. The as-synthesized nanowires are shown to form stable dispersions compared to nanoparticles in various organic and inorganic solvents.
[show abstract][hide abstract] ABSTRACT: Inorganic nanowires are expected to play a central role in the re-engineering of products with applications in composites, thin films, nanodispersions, energy conversion devices, sensors, nanoelectronic devices and optics. The synthesis of materials at the nanoscale might also help in the discovery of new phases with interesting properties. However, the synthesis strategies for inorganic nanowires is quite limited and have not reached the level of maturity needed for either bulk manufacturing or for controlling nanowire characteristics such as sub 10 nm diameters and different growth directions. In this regard, we report several synthesis strategies that potentially offer in-situ control over the resulting nanowire characteristics such as size, growth direction and an ability to form two-dimensional networks. The techniques described here could be scaled up easily for bulk production of various nanostructures. Our preliminary results suggest that the nanowires form stable dispersions in both organic and aqueous solvents compared to nanoparticles of the same material.