Elsevier

Journal of Crystal Growth

Volume 310, Issue 2, 15 January 2008, Pages 462-466
Journal of Crystal Growth

Low-temperature synthesis and electrical transport properties of W18O49 nanowires

https://doi.org/10.1016/j.jcrysgro.2007.10.038Get rights and content

Abstract

W18O49 nanowires are simply synthesized by the reaction between water vapor and tungsten powders in tube furnace at a low temperature of 600 °C. The nanowires have diameters of 20–50 nm, lengths several micrometers. XRD, TEM and SAED results show that the nanowires are of single crystalline monoclinic W18O49 structures with the growth direction [0 1 0]. The growth mechanism is analyzed. We investigate the temperature dependence electrical transport properties of individual W18O49 nanowires. The conductivity is 2.58 Ω−1 cm−1 at 290 K and 42.35 Ω−1 cm−1 at 500 K, respectively. And the electron activation energy is calculated to be about 0.26 eV.

Introduction

The miniaturization in electronics is promoting the development of nanotechnology. It will drive towards lower system costs and reduced power consumption. The studies in recent years have shown the possibility of fabricating functional devices from one-dimensional nanomaterials. The design and performance of these functional devices are based on the electrical properties of one-dimensional nanomaterials, such as carbon nanotubes, silicon nanowires, ZnO nanowires and SnO2 nanobelts. Field-effect transistors, bipolar transistors, single-electron transistors and metal–semiconductor diodes have been possible using carbon nanotubes and silicon nanowires [1], [2]. The investigations on the electrical transport properties of nanomaterials are fundamental for their application in fabricating functional devices [3], [4], [5], [6].

Tungsten oxide, for its applications in gas sensors [7], [8], electrochromic devices [9], photocatalysts [10] and field emission displays [11], has attracted much attention recently. Much effort has been taken to investigate their electrical properties, including superconductivity and charge carrying abilities. So far, the researches mainly focus on films [12], [13], [14], [15]. However, the electrical transport properties of one-dimensional tungsten oxide have rarely been studied for the difficulties in synthesis and measurement. Up till now, several methods have been reported to synthesize tungsten oxide nanowires. Li et al. grew quasialigned W18O49 nanotubes and nanowires in an infrared-heating furnace using a Ta wafer as substrate at high vacuum [16]. Zhou et al. obtained quasialigned nanotips of W18O49 at a temperature as high as 1400 °C [17]. Wang et al. synthesized W18O49 nanowires by annealing and then oxidizing WCx films [18]. Lee et al. synthesized colloidal tungsten oxide nanorods by hydrothermal using W(CO)6, Me3NO·2H2O and oleylamine as reagents [19]. As can be seen, the methods mentioned above either need special equipments, high temperature to evaporate the raw powders, or using poisonous reagents.

In this paper, we synthesized W18O49 nanowires by a simple and low-cost method at 600 °C. The morphology was characterized by XRD, TEM and SAED and the growth mechanism was given. The electrical transport properties of individual nanowires were investigated at a temperature ranging from 290 to 500 K.

Section snippets

Experimental details

The method used here is similar to that has been reported by Jin et al. [20]. There they used tungsten particles with diameters 0.6–1 μm and synthesized W18O49 nanoneedles with diameters 200–400 nm which have obvious dislocations at 800 °C. Here we develop the experimental conditions based on their results. In a typical process, an alumina boat loaded with tungsten (W) powders (99.9%, ∼0.2 μm) was placed at the center of the quartz tube inserting into a horizontal tube furnace. Two alumina boats

Results and discussion

Fig. 1(a) shows the general morphology of the products. The nanowires are of diameters ranging from 20 to 50 nm and lengths of several micrometers. It should be noted that there are a few nanoparticles in the products. Fig. 1(b) is the XRD pattern of the synthesized products, which shows there are WO2 (JCPDS: 32-1393) and metal W (JCPDS: 4-806) besides W18O49 (JCPDS: 5-392) in the products. The TEM image, as shown in Fig. 2, confirms that the nanowires are single crystalline. The down left inset

Conclusion

In summary, W18O49 nanowires were synthesized by a simple method at low temperature. The XRD, TEM and SAED results showed that the nanowires were single crystalline monoclinic W18O49 with the growth direction [0 1 0]. And the progress of growth was analyzed. The temperature dependence electrical transport properties of single W18O49 nanowires were investigated and the activation energy ΔE is about 0.26 eV.

Acknowledgments

This work was partly supported from “973” National Key Basic Research Program of China (Grant no. 2007CB310500), Chinese Ministry of Education (Grant no. 705040), and National Natural Science Foundation of China (Grant no. 90606009).

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