Nanotubes have opened the possibility of examining electronic transport through single-molecule wires of nanometer diameter with lengths of up to tens of microns - a model system in which to study the physics of electrons in one dimension. The existence of two flavors of nanotube - metallic and semiconducting - has also led to speculation about the possibility of an all-carbon molecular electronics technology. I will discuss the fabrication and properties of nanotube homo- and heterojunctions(1). The junction between two metallic nanotubes has a surprisingly high conductance, which may be understood as a result of compression of the junction by substrate forces, and points to the usefulness of nanotube networks as branching interconnects for molecular-scale devices. The metal-semiconductor junction acts as a nanoscale Schottky diode, and can be used as the basis of a three-terminal rectifier consisting of only a few thousand atoms. I will also discuss new techniques for imaging electronic transport in nanotube devices using a conducting-tip AFM(2). By using electrostatic force microscopy to image the local potential in current-carrying devices, the mean free path in semiconducting and metallic nanotubes has been measured. Individual scattering sites in semiconducting nanotubes can also be studied using scanned-gate microscopy.
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