Growth of carbon nanotubes by gas source molecular beam epitaxy

Multiwall carbon nanotubes have been grown by gas source molecular beam epi taxy in the presence of Ni catalyst. Some nanotubes show thinner bases comp ared with their heads. First- and second-order Raman scattering spectra are used to study the structure of samples with different initial thicknesses of Ni layers. The second-order 2D Raman mode of carbon nanotubes shows a do wnshift compared with the graphite-like structure. The growth of carbon nan otubes is found to depend on the size of the metal droplets. When the initi al Ni layer is either too thick or too thin, few carbon nanotubes are obser ved. The Raman spectra show graphite and glassy carbon structures for too t hick and too thin initial Ni layer films, respectively. Only when a proper range of Ni catalyst film is used, carbon nanotubes could be found. (C) 200 1 American Institute of Physics.