Growth orientation of carbon nanotubes by thermal chemical vapor deposition

Carbon nanotubes (CNT) were synthesized using thermal chemical vapor deposition. The diameters of these CNT were quite uniform with the length of the CNT up to several tens of micrometers. With the substrate surface normal either along or against the gravity vector, different growth orientations of CNT were observed by scanning electron microscopy. The Raman spectra were similar for samples synthesized at different locations. These results suggest that gravity affects the growth of long CNT with small diameters.