Spatial variations in the electronic structure of pure and B-doped nanotubes

The spatial homogeneity of electronic properties, as evidenced by the local density of states (LDOS) of pure and B-doped multi-walled carbon nanotubes, is investigated using scanning tunneling microscopy and tunneling spectroscopy. For pure nanotubes, the LDOS is found to be uniform except for the tip of the tubes. B-doped tubes, in contrast: show characteristic spatial variations in the electronic LDOS along their length. For both types of tubes, the LDOS associated with the tip structures is distinctively different from that seen anywhere on the tube body. Localized slates associated with the pentagonal defects present at the tube tips are identified for pure but not for B-doped tubes. The implications of spatial variations in the LDOS on electronic transport and field emission properties of carbon nanotubes are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.