Microstructure observations of silicon carbide nanorods
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The microstructures of –SiC nanorods synthesized by hot-filament chemical vapor deposition were studied in detail by high-resolution electron microscopy. Two distinct types of nanorods were identified. The longer nanorods (lengths > 0.1 m) contained globules at their tips and a relatively low density of stacking faults perpendicular to their [111] growth direction. It was also observed that SiC nanorods that grew along [100] direction contained no planar defects. Meanwhile, Ni was found to be an effective catalyst for SiC nanorod growth. The short nanorods (lengths < 50 nm), which contained no globules at their ends, can grow along [111], [100], or [112] direction. The growth of these nanorods was interpreted by a two-dimensional vapor–solid mechanism.
I. INTRODUCTION
The fabrication of nanometer-sized materials has gained considerable attention because of their potential uses in both mesoscopic research and in the development of nanodevices.1–6 Among these materials, SiC nanorods are effective materials for the reinforcement of various composite materials because of their high strength and stiffness combined with large aspect ratios. The strengths of the SiC nanorods measured were substantially greater than those found previously for larger SiC structures, and they approach theoretical values.4 The synthesis of SiC nanorods were first done successfully in 1995 by the carbon nanotube-confined reaction method.1 The diameters of the SiC rods produced were significantly smaller than those from the reaction of SiO with impure nanotubes at 1700 °C.7 This two-step reaction has also been employed for the synthesis of SiC nanorods via the carbon reduction of silica instead of using SiO directly.8 There are also reports of –SiC nanorods prepared by carbothermal reduction of sol-gel-derived silica xerogels containing carbon nanoparticles9,10 or chemical vapor deposition on granular active carbon with iron nanoparticles inside the pores.11 The synthesis of SiC whiskers with diameters in micrometers is much easier. The methods fall into the following three standard categories: carbothermal reduction of silica,12–18 decomposition of organic silicon compounds,19–21 and reaction between silicon halides and CCl4.22 The preferred method for mass production ap-
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Address all correspondence to this author. e-mail: [email protected]
2020
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 9, Sep 2000 Downloaded: 27 Mar 2015
pears to be carbothermal reduction of silica.23,24 This process has inherent advantages, including the availability of low-cost raw materials and the simplicity of the production procedure.17 In order to grow SiC in whisker morphology via the carbothermal reduction of silica, it is necessary to supply the reactants in a vapor form in the final step of the reaction.12,17 The most common vapor species are SiO and CO in an inert atmosphere,14,17 or SiO and CH4 in a hydrogen atmosphere.12,18 The geometrical factors of the whiskers, such as shape, size, aspect ratio, etc., are important factors that a
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