Formation of chains of graphitic nanoparticles by heating fullerene blacks covered with thin metal films

Strongly bent, fibrous carbon nanostructures with outer diameters usually between 35 and 90 nm were generated by the pyrolysis above 800 degrees C of a fullerene black which had been covered with a thin nickel film. Transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS) revealed that the material consists of chains of hollow elongated multi-wall graphitic nanoparticles. The worm-like nanostructures only arose from the nickel-covered parts of the fullerene black as checked with scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). Attempts to generate similar structures from commercial carbon blacks, arc-produced fullerene-free carbon blacks and glassy carbon failed. Substituting nickel by cobalt or molybdenum also did not lead to the generation of fibrous structures. Additionally, the pyrolysis-induced changes of metal films on graphite and glassy carbon and the direct interaction of nickel films with fullerene vapour were investigated. A growth model for the nanochains is proposed, which includes the diffusion of carbon through a metal particle, the segregation of carbon and the repeated surface melting and solidification of the metal.