Role of iron catalyst particles density in the growth of forest-like carbon nanotubes

Carbon nanotubes (CNTs) were fabricated by Chemical Vapour Depositon using a C2H2/H2 mixture. They were grown on Si/SiO2 substrate with Fe film as catalyst, deposited using thermal evaporation technique. The aim of this work is to emphasize the role of the Fe catalyst and the C2H2/H2 flow rate ratio to grow vertically aligned CNTs. Fe metal samples with the deposition times ranging from 1 min to 16 min were deposited and CNTs were grown with different C2H2/H2 flow rate ratio, from 5/95 to 30/70 by thermal CVD at 750 oC. Results show that CNTs were not vertically aligned with the longest catalyst deposition time for all flow rate ratios, while CNTs were always vertically aligned for deposition time less than 4 min and vertically aligned only for a C2H2 flow rate greater than 20% for the 7 min catalyst deposition time. Morphological and structural information about CNTs and Fe metal clusters were provided by field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). An accurate balance between the Fe metal clusters density and the C2H2/H2 flow rate ratio favours to achieve of a good vertical alignment