From helical nanowires, nanocrosses to aligned micro-carbon fibers
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From helical nanowires, nanocrosses to aligned micro-carbon fibers Hai-Feng Zhang1,2, Chong-Min Wang2, James S. Young2, James E. Coleman2 and Lai-Sheng Wang1,2 1 Department of Physics, Washington State University, 2710 University Drive, Richland, WA 99352, USA 2 W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
ABSTRACT We successfully synthesized helical core-shell crystalline SiC/SiO2 nanowires, core-shell crystalline SiC/C nano-crosses and well-aligned core-shell crystalline SiC/C fibers by using a chemical vapor deposition technique. For the helical crystalline SiC/SiO2 nanowires, the SiC core typically has diameters of 10-40 nm with a helical periodicity of 40-80 nm and is covered by a uniform layer of 30-60 nm thick amorphous SiO2. Detailed structural characterizations suggested that the growth of this novel structure was induced by screw dislocations on the nanometer scale. For the core-shell nanocrosses, the crystalline SiC core typically has diameters of 10 to 40 nm and is covered by a uniform layer of 80-110 nm graphitic carbon. The wellaligned SiC/C fibers were shown to be formed by two sequential steps: catalytic SiC growth and graphitic carbon nano-sheets coating. The helical nanowires and core-shell nanocrosses may have potential applications in nano-electronics. The formation mechanism of the carbon fibers suggested that fabrication of field emission filament carbon nano-fibers may be realized by using the aligned crystalline nanowires as templates. INTRODUCTION One-dimensional nano-structures have recently attracted great interest because of their potential applications as interconnects or functional components in future mesoscopic electronic, and opto-electronic devices [1,2]. The discovery of carbon nanotubes has significantly stimulated research activities into the syntheses and characterization of one-dimensional nanosystems, including semiconductor nanowires, coaxial nanocables, and nanobelts. In order to fabricate nano-devices with tailored properties, different types of nanostructures and nanojunctions will be needed [3-6]. In this paper, we report the syntheses of helical core-shell crystalline SiC/SiO2 nanowires, core-shell crystalline SiC/C nano-crosses, and well-aligned coreshell crystalline SiC/C fibers using a chemical vapor deposition technique. EXPERIMENTAL DETAILS The syntheses of helical nanowires, nanocrosses, and carbon fibers were performed in a horizontal alumina tube furnace using a silicon wafer as substrate, which was scratched using a 600 grit sand paper. Iron powders, held in an alumina sample boat were used as a catalyst to decompose methane, and were placed in the tube furnace upstream from the silicon substrate. The synthesis was carried out typically as the following: (1) Increase the temperature slowly to
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