Experimental studies of the formation process and morphologies of carbon nanotubes with bamboo mode structures

Carbon nanotubes (CNT) were synthesized by microwave plasma chemical vapor deposition, and the formation process and morphologies of bamboo mode structures were systematically analyzed. Thin films of Fe on Si substrates were used as the catalyst, and the CNT films were characterized with electron microscopy, Raman spectroscopy, and Auger electron spectroscopy. For growth up to 15 min, the films grow with vertically aligned CNT with evidence of amorphous carbon at the top surface. For longer growth times the films exhibit a layer of amorphous carbon and a CNT mat on top of the aligned carbon nanotube 'forest.' Transmission electron microscopy measurements displayed multiwalled CNT with bamboo structure and encapsulated tips some of which contained catalyst particles. Two kinds of bamboo mode structures were observed: cone shaped, and cylindrical. The results indicate that the CNT growth is predominantly of the base growth mode, and the formation of the compartments was attributed to the difference in the bulk and surface diffusion of carbon species at the catalyst.