Scanning tunneling microscopy and spectroscopy studies of single wall carbon nanotubes

Scanning tunneling microscopy and spectroscopy have been used to characterize the atomic structure and tunneling density of states of individual single wall carbon nanotubes (SWNT's) and ropes containing many SWNT's. Analysis of atomically resolved SWNT images shows that the nanotubes consist of a wide range of diameters and helicities with no one structure clearly dominant. Tunneling spectroscopy measurements made simultaneously on atomically resolved SWNT's exhibit semiconducting and metallic behavior that depend predictably on helicity and diameter. In addition the band gaps of the semiconducting tubes were also found to depend inversely on diameter. These results are compared to theoretical predictions, and the implications of these studies as well as important future directions are discussed.