Formation of Nanotubes, Nanowires, and Nanoparticles in a Hydrogen Arc

Abstract

Carbon nanotubes, nanowires, and nanoparticles are novel materials with numerous possible applications. Part of the interest in these materials lies in the intimate relationship between structure and properties. Understanding their growth process could lead to control of these properties. Hydrogen, which readily reacts with carbon, is used as the arcing atmosphere to help synthesize precursors for nanotube growth. In hydrogen, there is a direct correlation between the ability to remove graphitic sheets from the anode and the yield of nanotubes. This provides initial evidence that nanotubes can be formed by small graphitic sheets. In addition, encapsulated nanowires of Cu and Ge can be formed in the soot when arcing composite anodes in hydrogen but not in helium. To explain this, a mechanism is proposed using polycyclic aromatic hydrocarbon (PAH) molecules produced by the arc and metal nanoparticles as the precursors for nanowire growth. Experimental evidence for this mechanism is given by making Cu and Ge filled nanotubes using pyrene as the sole carbon source. In addition, it is shown that graphitically encapsulated magnetic nanoparticles can also be found in the soot when arcing a graphite/Ni anode in hydrogen.