One-step in situ synthesis and characterization of W 18 O 49 @carbon coaxial nanocables
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Mei Cai General Motors Research and Development Center, Warren, Michigan 48090-9055
Xueliang Suna) Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario, Canada N6A 5B9 (Received 25 November 2008; accepted 4 February 2009)
We demonstrate here in situ synthesis of bulk yield W18O49@carbon coaxial nanocables based on an easily controlled chemical vapor deposition process at relatively low temperature (760 C) using metallic tungsten powder and ethylene (C2H4) as the raw materials. Transmission electron microscope (TEM), energy dispersive x-ray (EDX), and x-ray diffraction (XRD) analyses indicate that the resultant nanostructures are composed of single-crystalline W18O49 nanowires, coaxially covered with amorphous carbon walls. A vapor–solid (VS) mechanism is proposed to interpret the formation of the nanocables. The effect of carbon sources on the nanocable growth was investigated. The results revealed that the introduction of carbon species not only causes the production of W18O49@C nanocable structures, but also obviously modulates growth behaviors and core/shell diameter ratio of the nanocables. The obtained nanocables may find great applications in catalyst systems and optical and electronic nanodevices because of their enhanced surface properties and in high chemical stabilities.
I. INTRODUCTION
One-dimensional (1D) nanostructures have drawn intensive research interest because of their unique applications in mesoscopic physics and nanoscaled devices.1–3 To tailor the physical and chemical properties of 1D nanostructures to a more diverse range, one of the most effective ways is to create heterostructures with different compositions and interfaces.4–6 Among various 1D heterostructures, the coaxial nanocable structure has become a significant class because of their wide applications in field effect transistors,7,8 light emitting diodes,9 solar cells,10 gas sensors,11 magnetic sensors12 and optical13–17 nanodevices. More recently, the synthesis of coaxial structures consisting of a carbon shell and a semiconductor or metallic core has become an emerging research field because of the distinct properties combining of carbon nanotube and other functional materials. Since 1D nanostructures can be easily oxidized and contaminated because of their high surface chemical reactivity, leading to the deterioa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0214 J. Mater. Res., Vol. 24, No. 5, May 2009
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ration of their performance, a carbon shell can provide an effective layer to ensure the stabilization and passivation of the active nanocore surface. To date, various metal18–23 or semiconductor24–31 @carbon coaxial nanocable structures have been developed, which raise some new research interest as a result of their distinct physical and chemical properties. As reported previously, Sn@carbon nanocables have been successfully synthesized by chemical vapor deposition,18 and the nano
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