Carbon nanotube intramolecular junctions

The ultimate device miniaturization would be to use individual molecules as functional devices, Single-wall carbon nanotubes (SWNTs) are promising can didates for achieving this: depending on their diameter and chirality, they are either one-dimensional metals or semiconductors(1,2). Single-electron transistors employing metallic nanotubes(3,4) and field-effect transistors employing semiconducting nanotubes(5) have been demonstrated. Intramolecula r devices have also been proposed which should display a range: of other de vice functions(6-11). For example, by introducing a pentagon and a heptagon into the hexagonal carbon lattice, two tube segments with different atomic and electronic structures can be seamlessly fused together to create intra molecular metal-metal, metal-semiconductor, or semiconductor-semiconductor junctions. Here we report electrical transport measurements on SWNTs with i ntramolecular junctions. We find that a metal-semiconductor junction behave s like a rectifying diode with nonlinear transport characteristics that are strongly asymmetric with respect to bias polarity. in the case of a metal- metal junction, the conductance appears to be strongly suppressed and it di splays a power-law dependence on temperatures and applied voltage, consiste nt with tunnelling between the ends of two Luttinger liquids. Our results e mphasize the need to consider screening and electron interactions when desi gning and modelling molecular devices. Realization of carbon-based molecula r electronics will require future efforts in the controlled production of t hese intramolecular nanotube junctions.