Nanostructured carbon generated by chemical vapor deposition from acetylene on surfaces pretreated by a combination of p
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ztia´n Korda´s and Ro´bert Vajtai Department of Experimental Physics, University of Szeged, H-6720 Szeged, Do´m te´r 9, Hungary (Received 14 February 2000; accepted 5 July 2000)
Chemical vapor deposition of carbon nanotubes by catalytic decomposition of acetylene on V2O5 microtube crystals is presented. The catalyst was prepared by laser irradiation of vanadium sheets and treated with cobalt acetate solution. The carbon deposits generated on this novel type of catalyst were characterized by transmission electron microscopy measurements. Both carbon nanofibers and carbon nanotubes were found to be formed. This catalyst system, generated by the combined laser irradiation and chemical impregnation methods, is a new and promising way to study the differences in the mechanism of the generation of nanostructures.
I. INTRODUCTION
Materials dispersed in nanometer size generally show very dissimilar properties compared to their appearance in larger measurements. This irregular behavior assures their application under unusual conditions. Intensive research effort has been spent on the preparation, characterization, and application of nanostructures. Among the various nanocompounds and composites, the structured carbon nanoparticles have attracted especially close attention. Carbon nanostructures, particularly nanofibers and nanotubes, are a focus of physical and chemical research because they can be used for hydrogen storage,1,2 as potential nanosensors, nanowires and nanoelectrical devices when the interior of the tube is filled with metal,3–12 and for polymer fillers. The application of carbon nanotubes has been summarized by Ajayan.13 Among the techniques are the arc discharge method first described by Iijima,14 laser-assisted reactions and evaporation-condensation, high-temperature pyrolysis performed in the absence or presence of catalysts, and electrochemical conversions.15–19 The properties of nanotubes and their modification have been widely investigated.20–27 The synthesis of Cu nanoparticles and microsized fibers using carbon nanotubes as a template28 or the inclusion of iron oxide in nanotubes29 has also been reported. It is known that most of the metals can be oxidized by laser irradiation.30–34 Taking into consideration that the laser beam transports very high energy focused on a very small surface, generally a fraction of one square millimeter, it can oxidize some portion of the metal target J. Mater. Res., Vol. 15, No. 10, Oct 2000
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generating distinctive structures of metal oxides on the surface. It has been shown experimentally and theoretically that the morphology of the oxide layer depends on the (spatial and temporal) temperature gradients causing inhomogenities in the reaction rate of oxidation, surface tension, and the transport properties (heat conductivity and diffusion constants).35,36 The regular micro- and nanostructures (microtubes and nanowires) are formed upon laser irradiation of a metal vanadium surface, resulting in a thousand times hig
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