Abstract: Helical carbon nanofibers with a symmetric growth mode were synthesized by the catalytic decomposition of acetylene using Cu-Ni alloy nanoparticles as the catalyst prepared by hydrogen-arc plasma method. The morphology of the coiled carbon nanofibers was examined by SEM, TEM and IR. We found that there were only two helical fibers symmetrically grown over a single Cu-Ni alloy nanoparticle, which was faceted with a regular shape(quadrangular, oblong, triangular and rhombus). The two coiled fibers have different coiled chirality, but have identical coil diameter, coil length, and fiber diameter. The angles between the two helical fibers grown on a single catalyst nanoparticles were different(60°, 90°, 110° and 160°). The IR analysis revealed that the molecular structure of helical nanofibers contained both unsaturated —CC— and saturated —CH₂— and —CH₃— groups. However, rectilinear carbon fibers were synthesized by the catalytic decomposition of acetylene with Cu nanoparticles and Ni nanoparticles as the catalyst prepared by hydrogen-arc plasma method.

Key words: Helical carbon nanofibers, Hydrogen-arc plasma, Cu-Ni alloy, Thermal decomposition