Thermal Analysis Study of the Growth Kinetics of Carbon Nanotubes and Epitaxial Graphene Layers on Them

With the aim of improving the yield and purity of carbon nanotubes (CNTs), we have studied the chemical vapor deposition (CVD) growth of CNTs with Fe-Mo powder catalyst and acetylene precursor by using the technique of in situ simultaneous thermal analysis (STA). We could distinguish this way the rapid catalytic growth stage of CNTs and the slow epitaxial growth stage of graphitic impurities on the nanotubes, which were discovered to be graphene layers. Both reactions were first order, and the activation energies were determined to be 177 and 189 kJ/mol, respectively. In the rapid-growth stage, the growth of CNTs could be further tuned from kinetically controlled regime to gas-diffusion-controlled regime, where the CNTs exhibit a longer growth time and a higher yield, using appropriately shaped crucibles. These results are helpful for both elucidating the growth mechanism of CNTs and improving the quality of mass-produced CNTs.