Carbon nanotubes have been grown on silicon substrates coated with metal catalysts containing Ni and Feat low temperatures by chemical vapor deposition using mixtures of acetylene and nitrogen at 90 Torr. At a growth temperature of 400 degreesC, all nanotubes are well aligned. However, these nanotubes are not made of perfect graphite as characterized by transmission electron microscopy and Raman spectra. The amount of carbon soot in the film increases apparently with increase of the concentration of acetylene and the growth temperature. But, as the growth temperature is raised to 500 or 600 degreesC, the graphitic-sheets begin to appear in the tube shell although the alignment of nanotubes becomes worse due to various growth rates for different sizes of nanotubes. Methane and carbon monoxide reactants are studied and found to be unable to grow carbon nanotubes at the conditions employed for acetylene to successfully grow nanotubes. Field emission of the carbon nanotube film grown at 400 degreesC. is also measured. The turn on voltage is 11 V mum(-1).