Scanning tunnelling microscopy and spectroscopy of short multiwall carbon nanotubes

We report on the structural analysis of multiwalled carbon nanotubes (MWCNTs), produced by the DC arc discharge method in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. Microscopic scale 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°). For MWCNT ropes, 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 MWCNTs span the metallic-semiconductor regime. Unlike other MWCNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as components for molecular electronic devices.