Tunneling spectroscopy on carbon nanotubes using STM

Single-wall carbon nanotubes (SWNTs) prepared on the graphite substrate were investigated by a low-temperature scanning tunneling microscope at 77 K. From the tunneling spectra with high-energy resolution obtained at 77 K, both metallic and semiconducting SWNTs were found in the same bundle. For the metallic SWNT, the conductance curve inside the first peak is finite and quite flat. The width between the first peaks is obtained as 1300 meV. Fine structures due to the anisotropy of equi-energy contours around the K point were observed just outside the first peaks. The observed gap width for the semiconducting SWNT is 600 meV. The conductance curve, which has broad peaks around V = + 80 mV was also observed. (C) 2002 Elsevier Science B.V. All rights reserved.