The Mo-containing compound is probably an oxide although detailed compositional analysis has yet to be carried out. 10 mg catalyst was placed in a quartz boat and heated to 1200C in Ar gas flowing through a quartz tube in an electrical furnace. Once the temperature reached 1200C, the Ar flow was shut off and pure CO gas was introduced at a flow rate of 1,200 sccm. The original light-blue catalyst material had become black with a slight increase in volume. One difficulty in the catalytic production of multiwall nanotubes is the inability to operate at temperatures higher than 800-900 o C, since above these temperatures the rate of pyrolysis of the hydrocarbon feedstock overwhelms the rate of tube growth, resulting in an undesirable amorphous overcoating.
Higher temperatures are desirable in order to anneal away defects that form in the growing nanotube.
Carbon monoxide as a carbon source does not suffer from this problem since it decomposes in the vapor at a significant rate only at much higher temperature. We operated at 1200 o C since this is the temperature known to produce the optimum fullerene yield, an indication that nanotubes should anneal at this temperature. The present observation eliminates this possibility by showing that attachment of catalytic particles to their tubes survive exposure to temperatures similar to that in the LV experiment, as well as sonication. The nanotubes of Fig. 1 exhibit several other notable features. First, they are isolated instead of forming bundles or ropes as in LV and arc formation, implying that growth is individual rather than cooperative, as we believe is the case for LV and arc-grown tubes.