Atomic structure and electronic properties of single-wall carbon nanotubesprobed by scanning tunneling microscope at room temperature

A detailed three-dimensional structural analysis of single-walled carbon na notubes was carried out using a scanning tunneling microscope (STM) operate d at room temperature in ambient conditions. On a microscopic scale, the im ages show tubes condensed in ropes as well as tubes which are separated fro m each other. For a single-wall nanotube rope, the outer portion is compose d of highly oriented nanotubes with nearly uniform diameter and chirality. On separated nanotubes, atomically resolved images show variable chirality ranges between 0 degrees - 30 degrees, and variable diameter (1-3 nm), with no one type dominant. From STM and scanning tunneling spectroscopy measure ments we confirmed the correlation between chirality and the electronic pro perties, namely the tuning from metallic to semiconducting. We also observe d a rectifying behavior correlated with the chiral angle of 25 degrees, an important observation for nanodevices application. (C) 1998 American Instit ute of Physics. [S0003-6951(98)01552-6].