Tungsten oxide nanowires synthesized by a catalyst-free method at low temperature

We report the synthesis of tungsten oxide W 18 O 49 nanowires by thermal evaporation at low temperature without using catalysts. By placing tungsten powder in the high temperature zone at 650 °C and tungsten substrate in the low temperature zone at 400 °C of a tube furnace, W 18 O 49 nanowires with diameters of 10–50 nm are produced with high yield. The nanowires extend to 500–1500 nm length, and the cross-sectional shapes are circular or polygonal. The roles of the source material, the pre-oxide layer on the substrate and the temperature of the reactor are also investigated. It is shown that the presence of oxygen on the W surface is essential for tungsten oxide nanowire growth.