Palladium (Pd), chromium (Cr), and platinum (Pt) are used as co-catalysts to decrease the growth temperature of carbon nanotubes to 500-550 degrees C. Pd is found to be the most efficient co-catalyst for the growth of carbon nanotubes on cobalt-nickel catalytic particles deposited on a silicon oxide substrate by thermal chemical vapor deposition using C2H2. High-resolution transmission electron microscopy reveals the bamboo-shaped carbon nanotubes grown at 500 degrees C using Pd, while the curled carbon nanofibers are grown at 550 degrees C using Cr.