Scanned Probe Microscopy of Electronic Transport in Carbon Nanotubes
  We use electrostatic force microscopy and scanned gate microscopy to probe the conducting properties of carbon nanotubes at room temperature. Multi-walled carbon nanotubes are shown to be diffusive conductors, while metallic single-walled carbon nanotubes are ballistic conductors over micron lengths. Semiconducting single-walled carbon nanotubes are shown to have a series of large barriers to conduction along their length. These measurements are also used to probe the contact resistance and locate breaks in carbon nanotube circuits. 
A. Bachtold, M. S. Fuhrer, S. Plyasunov, M. Forero, Erik H. Anderson,   A. Zettl and Paul L. McEuen