The optimization of water assisted chemical vapor deposition (WA-CVD) was carried out to synthesize ultra long, vertically aligned, densely packed carbon nanotube (CNT) forests. The effect of various WA-CVD parameters (viz. the flow rate of the reactant gas mixture and its injection temperature, growth kinetics, ramp rate and growth temperature) on the height of the CNTs was studied. A hypothesis for catalytic activity is proposed on the basis of the X-ray photoelectron spectroscopic analysis of the CNT grown substrates and further verified at the optimum condition. The effect of temperature on the growth of the CNTs is studied. The gas flow rate and injection temperature influence the onset of oxidation of the substrates, which in turn affects the CNT growth rate. A growth kinetics study is performed in order to monitor the growth temperature. The role of the onset of oxidation of the iron catalyst in the growth of the CNTs is studied by varying the ramp rate. The precise CNT growth temperature for WA-CVD is determined by growth temperature studies. The optimum condition allows ～2.2 ± 0.002 mm long CNTs to be obtained.
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