Tungsten Oxide Nanorods Growth from Heated Tungsten Foils

Details: Category: Tungsten Information; Published on Thursday, 05 February 2015 18:35; Written by cq; Hits: 1504

Tungsten oxides nanostructures have exhibited application perspectives in such fields as electrochromic (EC) devices, photocatalysis, gas sensing, adsorption of organic dyes, etc. So far, in most high-temperature-reaction fabrications of the tungsten oxide nanostructures, the reactant sources and the substrates are separated. Occasionally, tungsten oxide nanostructures are grown directly from the metallic tungsten, which serves as both the reactant source and the substrate. The advant ages of direct heating method include short fabrication time, convenient manipulation, less expensive instrumentation and easy accession to high reaction temperatures. Most importantly, tungsten ox-ide nanostructures can grow directly from, instead of depos-iting on, the substrates. Therefore, a number of desired properties, such as good adhesion and low contact interface resistance, can be expected.

As previously reported, a fast heating chemical vapor deposition (CVD) system was developed, in which the temperature of the carbon substrate could be raised to 1800°C in 15 seconds with the passage of large electric current. Combined structures of conical carbon fiber and carbon nanotube (CCF/CNT), which had large length, good straightness and perfect crystallinity, were fabricated using this system. Recently, tungsten oxide nanostructures were also attained with similar instrumentation.

Nanorods of W18O49, an oxygen-deficient nonstoichiometric tungsten oxide, were fabricated by directly heating W foils. In the fabrication, the W foils functioned as both the sub-strates and the reactant sources. Other necessary conditions included the coverage of the substrates with KBr and the introduction of low pressure wet oxygen. The oxidized W surface and the KBr on it combined into eutectic droplets and tungsten oxide segregated from them due to supersatu-ration. This growth is referred to as an SLS process. Field emission was obtained from the such-fabricated W18O49 nanorods and the UPS analysis suggested that the emitted electrons were likely to have come from the conduction band, impurity levels and/or surface states of these nanorods.

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