Carbon nanotubes are filled with copper by means of chemical vapor deposition. Control of the density of copper in the plasma is crucial and is accomplished by adjusting the length of the copper electrodes that are exposed to the tungsten heating filament. Both simple and branched Cu-filled nanotubes were grown. Most of the branched nanotubes branch only once to form a regular trilateral starburst structure; others branch repeatedly in simple dendritic patterns. A model to account for the filling and growth characteristics is proposed based on observations made with a high-resolution transmission electron microscope and selected area electron diffraction.

Well-aligned carbon nitride nanotubes are fabricated by microwave plasma assisted chemical vapor deposition using iron as the catalyst. These nanotubes are linearly polymerized by carbon nitride nanobells with catalyst particles in the root, as revealed by high-resolution transmission electron microscopy. Carbon nitride nanotube film is analyzed by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Raman spectroscopy. Both XPS and AES reveal a nitrogen content of about 2% in the film. Raman spectroscopy exhibits a good crystallization of these carbon nitride nanotubes. Electron energy loss spectroscopy is used to study the local distribution of nitrogen in a single nanotube, which indicates that nitrogen prefers to locate at curved graphite sheets, at the top of the nanobells, and that incorporation of nitrogen results in the decrease of the crystallization. Based on these results, a growth model is proposed to explain this periodically stacked nanobell structure. In this model, we propose that graphite sheets only precipitate along the surface of catalyst particles and that lower growth rate at the top curve surface of the bell-like catalyst particle is the key factor influencing formation of this special microstructure. A heterojunction between a tubular carbon nanotube and a carbon nitride nanobell also has been fabricated by a two-step growth technique. And short carbon nitride nanotubes with a few nanobells or even just one nanobell are obtained by both physical and chemical methods. Furthermore, we studied the field emission properties and have obtained a threshold field of as low as about 1 V/μm. A novel side-emission mechanism has been proposed based on the special polymerized nanobell structures.