Structures of carbon nanotubes studied by HRTEM and nanodiffraction

Abstract

Nanodiffraction, with an electron beam of diameter 1 nm, has been used in conjunction with high resolution electron microscopy (HREM) and selected area electron diffraction to investigate the structures of carbon nanotubes having diameters of a few nanometers. It is shown that, in addition to nonotubes of circular cylindrical cross-section, with zero, one or several helix angles, there are many tubes having polygonal cross-sections, made up of flat regions joined by regions of high, but uniform curvature. The HREM evidence for such structure is that the patterns of lattice fringes on the two sides of the tube may be very different, with spacings varying from the 0.34 nm given by circular cylinder tubes, up to 0.41 nm. The nanodiffraction patterns show that the flat regions of the polyhedral tubes may have a well crystallized graphite structure but may also show considerable rotational disorder.