Temperature and gas pressure effects in vertically aligned carbon nanotube growth from Fe-Mo catalyst

Vertically aligned carbon nanotubes are grown from Al2O3-supported Fe-Mo catalyst in a hot filament chemical vapor deposition apparatus. We compare the effect of carbon nanotube growth on deposition of 0.5 and 1 nm thick Fe catalyst layers before and after deposition of 0.1 and 0.2 nm thick layers of Mo. We observe that the order of deposition plays a role in the height of the nanotube arrays, especially evident during growth at elevated reaction pressures where carbon flux is higher. We investigate the role of temperature and pressure on features of the nanotube arrays such as height, alignment, quality, volumetric density, and diameter distribution for each of the catalyst thicknesses and for each case of Fe/Mo and Mo/Fe. We compare our results to those obtained from carpets grown from pure Fe catalyst, and observe that a Mo cocatalyst call be advantageous regardless of how it is deposited. However, we find that the order of deposition plays a key role in the temperature and pressure range in which optimal single-walled carbon nanotube growth occurs.