Growth of multiwall carbon nanocoils using Fe catalyst films prepared by ion sputtering
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shad Muhammad College of Materials Science and Engineering, Chongqing University, Shapingba, Chongqing, 400044, People’s Republic of China (Received 28 December 2012; accepted 8 April 2013)
Carbon nanocoils (CNCs) with different diameters have been synthesized on different substrates by thermal chemical vapor deposition using Fe films as catalysts prepared by ion sputtering. It is found that CNCs with diameters greater than 100 nm are obtained as the main products in large quantities on Fe film coated indium tin oxide substrates. However, on Fe film coated SiO2 substrates, multiwall CNCs (MWCNCs) along with carbon nanotubes (CNTs) are grown, and the yield of MWCNCs is decreased rapidly with a lower Fe film thickness. The as-grown MWCNCs with observed coil diameters less than 100 nm and filament diameters less than 30 nm are much thinner than the conventional CNCs. Plate-like catalyst particles with sizes much larger than the filament diameter of the MWCNCs are observed at the roots of these MWCNCs, indicating a base growth mechanism. Furthermore, it is also observed that large particles with irregular shapes lead to the growth of helical MWCNCs, while large particles with steady circular shapes tend to grow as straight CNTs. Based on the experimental results, a growth model for MWCNCs is proposed.
I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.107
scopic scale, MWCNCs can be used in high-performance composite films with high conductivity, good elasticity and toughness.14 Meanwhile due to their helical structure, MWCNCs are also considered as good materials for highly efficient electromagnetic wave absorbers.15 The synthesis of conventional CNCs including their structure, formation, and growth mechanism has been reported in many articles.4,10,16–19 So far, many research groups have synthesized CNCs with large coil diameters (greater than 50 nm) in large quantities.16–18,20–22 However, still there has been no breakthrough in the preparation techniques for growing MWCNCs with small coil diameters (less than 50 nm). The main reasons are that the growth mechanism for the MWCNCs is not clear and the optimum catalysts have not been found. Therefore, the growth of MWCNCs can’t be effectively controlled, leading to their lower production rate. In general, MWCNCs are synthesized by catalytic chemical vapor deposition (CVD) using hydrocarbons as reaction gas and transition metals as catalysts.7,23–25 The first experimental observation of the production of MWCNCs was done in 1994, when Zhang and Amelinckx et al.26,27 synthesized MWCNCs by catalytic deposition of acetylene over a silica-supported Co catalyst in a CVD system at 700 °C. Similarly, Lu et al.28 have prepared MWCNCs by catalytic CVD on finely dispersed Co nanoparticles supported on silica gel under reduced pressure and relatively low gas flow rates. Tsuchiya et al.29 have reported a method to
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Ó Materials Research Society 2013
Three-dimensional (3D) helical materials have attracted worldwide attention due to t
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