  Our group recently reproduced the water-assisted growth method, so-called
"super growth", of millimeter-thick single-walled carbon nanotube (SWNT)
forests by using C2H4/ H2/ H2O/ Ar reactant gas and Fe/ Al2O3 catalyst. In this
current work, a parametric study was carried out on both reaction and catalyst
conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm)
yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3
support enhanced the activity of Fe, Co, and Ni catalysts. The growth window
for the rapid SWNT growth was narrow, however. Optimum amount of added H2O
increased the SWNT growth rate but further addition of H2O degraded both the
SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT
growth, but again, further addition decreased both the SWNT growth rate and
quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly
enhances the SWNT growth rate by supplying the carbon source to the catalyst
nanoparticles. The origin of the narrow window for rapid SWNT growth will also
be discussed.
