In order to understand the intrinsic electronic properties of carbon nanotubes, it is important to eliminate the contact effects from the measurements. This can be accomplished by using a conductive-tip atomic force microscope cantilever as a local electrode to obtain length-dependent transport measurements. In this talk, I will review the previous experimental efforts in this area. I will describe how to obtain a reproducible and stable electrical contact between conductive AFM cantilevers and carbon nanotubes. I will report on resistance versus length R(L) measurements in long channel carbon nanotubes (up to 130 micrometer) at room temperature. For semiconducting carbon nanotubes in the on-state, R(L) is linear. In the depleted state, R(L) is linear for long channel lengths (>10 micrometer), but non-linear for short channel lengths due to the long depletion lengths in one-dimensional semiconductors. Transport remains diffusive under all depletion conditions, due to both low disorder and high temperature.

Keywords: carbon nanotubes