Nanotechnology’s Wonder Material: Synthesis of Carbon Nanotubes - Hierarchical Nanostructures for Energy Devices - page 53

d n 3 r 4 n g | 6

Figure 3.11 Growth termination data obtained with different compositions of
unpurified and purified ethylene and hydrogen feedstock. The gas
purification results in striking differences in the catalyst lifetime and
growth yield.
Reprinted with permission from ref. 46. Copyright 2011 American
Chemical Society.

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high-resolution data clearly show that this model does not provide an ad-
equate description.
Third, the complicated nature of the process places very stringent re-
quirements on the experimental setup. For instance, purification to remove
gas impurities is necessary for reproducible CNT growth. This is because the
oxygen-containing species can make the growth chemistry very complicated
by promoting or demoting catalysts depending on their molecular forms and
concentrations. 43,52 Indeed, different gas compositions produce strikingly
different trends of growth deactivation (Figure 3.11), which could in turn
produce misleading analysis. Finding the most ecient gas precursor could
be a valuable complement to these efforts as it would simplify the GPR
kinetics. 6,42,44,45

3.3 Conclusion
Carbon nanotube synthesis represents a striking example of a simple system
that can produce rather complicated behavior. Given the amount of effort
that has gone into understanding CNT growth to date, it is remarkable how