Tungsten trioxide nanomaterials are of tremendous interest due to their potential use as electro chromic, gas sensing, and photo catalyst materials. The synthesis of doped and undoped tungsten oxide nanowires is done using either tungsten foils or powders as sources. Utilizing chemical vapor transport of metal oxide vapor species andoxygen flow over hot-filaments onto substrates, metal oxide nanowires can be fabricated.

In vapor phase synthesis route, the chemical vapor of tungsten oxide is transported onto substrates kept at temperatures higher than the decomposition temperature resulting in tungsten nanowires. The synthesis of tungsten oxide nanowires can also be accomplished without the use of any catalysts or any medium.

Hot filament CVD reactor setup is used for the synthesis. It consists of a quartz tube housed in a tube furnace heater with the ends connected to the necessary accessories for flow and pressure control. A tungsten filament of small diameter and long length is used as the tungsten source. The tungsten filament is always heated to a temperature of about 1950 K and quartz boats are employed to curtail the deposition directly onto the tube walls. The substrates (quartz and fluorinated tin oxide coated quartz slides) are placed on the boat and heated for 10-15 minutes. The synthesized nanowires are collected in a dry powder form by scraping the material from the quartz substrates.

The nanowires obtained are oxygen deficient W18O49 phase and subsequent oxidation of these substrates in an oven changes the phase to WO3 as indicated by a change in color from blue to green. Tungsten oxide nanowires can remain in the solution for longer periods of time without sediment or any kind of agglomeration compared to nanoparticles in organic solvents.