Control over the Diameter, Length, and Structure of Carbon Nanotube Carpets Using Aluminum Ferrite and Iron Oxide Nanocrystals as Catalyst Precursors

Both colloidal iron oxide and aluminum ferrite nanocrystals can initiate the growth of vertically aligned carbon nanotube (CNT) carpets through water-assisted chemical vapor deposition (CVD). The outer diameters of the CNTs ranged from 3 to 18 nm, and this dimension correlated well with the diameters of the starting nanocrystals. The smallest particles (4 nm aluminum ferrite nanocrystals) yielded CNT carpets with high percentages (60%) of single-walled CNT species, whereas larger particles (iron oxide nanocrystals over 25 nm) formed carpets with more double, triple, and larger multiwalled structures. CNTs grown by aluminum ferrite nanocrystals were uniformly of higher quality (<i>I</i>_G/<i>I</i>_D = 11.4) than comparable materials formed from pure iron oxides (<i>I</i>_G/<i>I</i>_D = 9.8). We speculate that the presence of aluminum in the nanocatalyst may slow the acetylene decomposition at the catalyst surface, leading to less production of amorphous carbon material