Vertically aligned bamboo-like carbon nanotubes (CNTs) are successfully synthesized on Ni-coated Si (NUSi) substrates by hot-filament-assisted radio frequency (rf) magnetron sputtering. Transmission electron microscopy analysis reveals that a bamboo-like structure is formed inside the nanotube that has a catalytic Ni nanoparticle on the tip. It is likely that moderate carbon particle energy plays an essential role in synthesizing CNTs by sputtering. To verify its importance, we conduct a bias-sputtering experiment to test the effect of negative voltages on the energy of the carbon particles. Furthermore, we find that the diameter and density of the aligned bamboo-like CNTs can be controlled by changing the number density of Ni nanoparticles on Si substrates. (C) 2003 American Vacuum Society.