A Scalable Method for the Synthesis of Metal Oxide Nanowires

We report a novel, scaleable and versatile method for large scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates including amorphous quartz, fluorinated tin oxide, etc. The synthesis concept uses the chemical vapor transport of metal oxide vapor phase species onto substrates using air or oxygen flow over hot-filament sources. The hot-filaments were designed to provide uniform heating and gas phase composition over large substrate areas. The results show that the nucleation densities could be varied from 10/cm to 10/cm with decreasing substrate temperature. A thermodynamic model for determining the nucleation density and nanowire diameter is presented. The analysis indicates that the nucleation for nanowires occurs through condensation of sub-oxide, WO2 species. This is in contrast to WO3 species condensation into WO3 solid phase for nanoparticle formation. The dispersion behavior of as-synthesized nanowires in aqueous and organic solvents is also studied.