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 deg C and tungsten substrate in the low temperature zone at 400 deg 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.
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