Scanning tunneling microscopy and spectroscopy of multiwall carbon nanotubes

We report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC are discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30 degrees). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are equally visible by STM tip. This suggests that the stacking nature of MWNTs has no detectable effects on the electronic band structure of the tube shells. Unlike other MWNTs produced by are discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices.