Carbon Nanotubes Intramolecular Junctions

Single-wall carbon nanotubes (SWNTs) can be either one-dimensional metals or semiconductors depending on their diameters and chiralities. These remarkable electronic properties and their small sizes (diameters ~1 nm) make SWNTs an ideal candidate for the ultimate miniaturization of electronic devices. Single-electron transistors employing metallic nanotubes and field-effect transistors employing semiconducting nanotubes have been demonstrated. More fascinating intramolecular devices have also been proposed. For example, by introducing a single pentagon-heptagon pair into the hexagonal carbon bond network, two pieces of nanotubes with different atomic and electronic structures can be seamlessly fused together, thereby creating metal-metal, metal-semiconductor, or semiconductor-semiconductor junctions. These junctions can be envisioned as building blocks for future molecular electronics based entirely on carbon. Here we report, to our knowledge, the first electrical measurements of well-defined nanotube intramolecular junctions. A metal-semiconductor junction is found to act like a rectifying diode, that is it exhibits nonlear transport characteristics that are strongly asymmetric with respect to bias polarity.