Tungsten Oxide Nanowires

Compared with other transition metal oxides, ungsten oxides have attracted great attention and have been investigated extensively due to their outstanding electrochromic, optochromic, and gas-chromic properties. ith those distinctive prop-erties, tungsten oxides have been used to makeflat panel displays, photoelectrochromic smart win-dows and gas sensors. Non-fully oxidized tungsten oxides (WO3x), such as W20O58, W18O49andWO2, are of particular interest because of their unique electronic characteristics, e.g. tungsten oxide has been found to be a semiconductor, a conductor or a superconductor in different oxidization states. Since one-dimensional tungsten oxide nano-materials exhibit superior properties in some promising applications compared with bulk materials, much effort has been made to synthesize tungsten oxide nanowires by using different methods, including a soft-chemistry approach, the chemical vapour deposition (CVD) method, hot-filament-assisted synthesis, flame synthesis and multistage field enhancement of tungsten oxide nanowires.

Tungsten oxide nanowires of diameters ranging from 7 to 200 nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour–solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W18O49. I–V curves are measured by an in situ transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I–V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I–V curves by using a metal–semiconductor–metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.

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