GROWTH-BEHAVIOR AND GROWTH DEFECTS OF CARBON NANOTUBES

The growth behavior and growth defects of carbon nanotubes have been examined by high resolution electron microscopy. Results have shown that both axial extension and radial thickening mechanisms are involved in the growth of carbon nanotubes. Depending on the nucleation conditions, a tube can have either a circular or a polyhedral cross-section. However, the growth mechanisms for the circular tubes and for the polyhedral tubes are apparently the same. The existence of nanotube-nanoparticle assemblies suggests that the formation processes of tubes and of particles are closely related. Several growth defects have been identified in the present study, such as incomplete sheets, U-turn growth, disordered sheet stacking, growth step, dividing wall, curved tube, and sharp bend. The mechanisms involved in the formation of these defects have been discussed. Graphitic sheets are found to possess a great flexibility. The smallest tube observed in the present study has a diameter of approximately 0.7 nm, corresponding to the diameter of a C60 molecule. Excess illumination by electron beam will result in radiation damage of tubes. The radiation damage takes place over the entire illuminated area while the growth defects only occur in limited regions.