ABSTRACT
The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates has been developed. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. Based on this technology, a 13C isotope labeling method was developed for revealing the growth mechanism of the multi-walled nanotubes (MWNT) made by chemical vapor deposition (CVD), a topic that has been under extensive investigation since the discovery of the carbon nanotube. Various theoretical models of nanotube growth have been suggested, however, direct experimental evidence to support any of the models is scarce. The isotope labeling method established a relationship between the feeding sequence of 13C2~ and 12C2~ and the locations of 13C and 12C atoms in the nanotubes relative to the catalyst particles. The results provided unambiguous evidence supporting the extrusion growth model of MWNTs. Moreover, the isotope labeling method represents a reliable chemical approach to nanotube intra-molecular junctions that may exhibit interesting and useful properties.
