Synthesis of Y-branching multiwalled carbon nanotubes with a bamboolike structure
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G.H. Li Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China (Received 13 June 2002; accepted 19 August 2002)
Y-branching multiwalled carbon nanotubes with a bamboolike structure were grown by chemical vapor deposition from a C–H–N gas system when B2O3 and Ti was supplied. Transmission electron microscopy images reveal that these novel junctions contain a tube branched into two tubes with nearly the same diameter. In addition, the tube walls show perpendicularly stacked graphite planes, which take on a bamboolike structure. The influence of preparation conditions on the structure of these carbon nanotubes is discussed. This novel structure may offer promising application for nanotube-based composites.
Carbon nanotubes (CNTs) are one of the most promising materials for the fabrication of nanotechnological devices in the future. Considerable research efforts are focused on the investigation of their structure, as well as their remarkable mechanical and electric properties. One of the interesting facets is the multitude of novel shapes, such as nanosprings, bamboo trunks, and connectors, observed under different processing conditions. Another fascinating application of this new form of carbon is use as an excellent candidate for composite reinforcement, which comes from the exceptional mechanical properties of CNTs combined with their low density. In the behavior of nanotube-based composites, the interaction at the nanotube/matrix interface is critical.1,2 The bamboo trunks and the branching structures in CNTs, such as Y and L junction, are attracting increasing interest because they are potentially able to bring in new mechanical properties and improve nanotube/matrix wetting and adhesion. At the same time, the branching CNTs may bring in novel electrical properties.3–5 These features may be essential for carbon nanotube-based composites and nanotechnology. The branching CNTs have been synthesized by the arc-discharge method6 and chemical vapor deposition (CVD) method, such as hot-filament CVD,7 thermal decomposition of fullerene,8 MPE-CVD,9 and thermal CVD.10 The Y-junction CNTs grown in the latter method
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J. Mater. Res., Vol. 17, No. 11, Nov 2002
are reported to present a rectifying effect in two-terminal I–V characteristics.11 In this communication, we report our observation of Y-shaped multiwalled CNTs (MWCNTs) with bamboolike structure, which may offer promising application for composite materials and microelectronic devices. Our procedure for preparing CNTs is described as follows: Ti powder (>100 nm) and B2O3 powder were mechanically mixed and pressed into pills and then were placed in a tubular furnace with a flow of 40 ml/min H2 and 80 ml/min N2 while the temperature was increased to 900 °C at a rate of 10 °C/min. Then, additional flow of 8 ml/min C2H2 for 2 h was introduced. Finally, the system was cooled in N2 atmosphere to room temperature. In this procedure, the total
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