The structure of the carbon nanotube and its surface topography probed by transmission electron microscopy and atomic force microscopy

The structure, morphology and surface topography of multilayer carbon nanotubes have been studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The carbon nanotube three-dimensional structure, and especially that near the cap regions, is resolved by use of these two complementary techniques. We have found that a large proportion of nanotubes have a cylindrical shaped body, with a significant number being polygonal in appearance. Polygonal caps with extended flat surfaces are also directly imaged by the TEM and AFM studies. We have achieved atomic resolution AFM imaging of a nanotube surface, showing the hexagonal arrays on the top layer akin to the graphite structure. These are arranged helically with respect to the tube axis. The observation of superpatterns, deviation of the surface trigonal patterns to nearly hexagonal patterns and an increase in interlayer distance compared with graphite, indicate stacking disorders between successive cylindrical layers. Dislocation defects on the surface can be clearly imaged by the AFM and it appears that, although most tubes appear to be formed by concentric tubes, some spiral structures can also occur.