Two opposite growth modes of carbon nanofibers prepared by catalytic decomposition of acetylene at low temperature

Helical carbon fibers were synthesized by the catalytic decomposition of acetylene as carbon source at low temperature of 240–260 C with two nanocopper catalysts prepared by the hydrogen-arc plasma method and thermal decomposition of copper tartrate. Two growth modes for helical carbon fibers were obtained. One is mirror-symmetric growth mode, and the other is asymmetric growth mode. In the two growth modes, there were always only two helical fibers in regular shapes that were grown over a single copper nanoparticle. The two helical fibers had identical coil diameter, coil length, fiber diameter, cycle number, tight coil pitch, and cross section. In mirror-symmetric growth mode, the two helical fibers had absolutely opposite helical senses. The catalyst particle size was less than 50 nm and the coil diameter was\100 nm. Whereas in asymmetric growth mode, the two helical fibers had absolutely identical helical senses. The catalyst particle size was larger than 200 nm and their coil diameters reached 1 lm. The catalyst particle size had considerable effect on the growth mode for helical carbon fibers.