The growth behavior and growth defects of carbon nanotubes were examined using high-resolution electron microscopy. The results showed that both axial extension and radial thickening mechanisms were involved in the growth of carbon nanotubes. Depending upon the nucleation conditions, a tube could have either a circular or a polyhedral cross-section. However, the growth mechanisms for the circular tubes and for the polyhedral tubes were apparently the same. The existence of nanotube-nanoparticle assemblies suggested that the formation processes of tubes and of particles were closely related. Several growth defects were identified in the present study, such as incomplete sheets, U-turn growth, disordered sheet stacking, growth step, dividing wall, curved tube and sharp bends. Graphitic sheets were found to possess great flexibility. The smallest tube observed in the present study had a diameter of approximately 0.7nm, corresponding to the diameter of a C60 molecule. Excess illumination by electron beams resulted in the radiation damage of tubes. The radiation damage occurred over the entire illuminated area, while the growth defects occurred only in limited regions.

Growth Behavior and Growth Defects of Carbon Nanotubes. M.Liu, J.M.Cowley: Materials Science and Engineering A, 1994, 185[1-2], 131-40