Synthesis and characterization of tungsten oxide nanorods

Single crystalline nanorods (15–200 nm in diameter and hundreds nanometers in length) have been formed on the carbon-covered W wires by simple electric heating under a vacuum of 5 × 10⁻⁴Pa. The chemical composition and crystalline structure of the nanorods were carefully investigated by various characterization techniques such as scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, energy dispersive x-ray spectroscopy and electron energy loss spectroscopy. After ruling out any possible existence of carbon nanotubes (CNTs), tungsten carbide, W–Fe alloying, and formation of other types of tungsten oxides, monoclinic W₁₈O₄₉phase has been well identified. The mechanism of nanorod formation of sub-tungsten oxide (∼WO_2.7compared to WO₃) will be discussed in relation to the sample preparation conditions.