Quantum transport in low-dimensional organic nanostructures

We have studied three low-dimensional systems with sub-micron dimensions: a single polyacetylene (PA) nanofiber; a single-walled carbon nanotube (SWNT)-rope; and a lithographically prepared stripe of poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV). In each case, the sample was contacted to four-probe electrodes, with 100-nm spacing and various electronic transport properties such as the I-V characteristics, the temperature dependence of resistivity and the gate voltage dependence of the transport current were measured. The PA nanofiber was found to be non-ohmic with a room temperature conductivity of ∼0.1 S/cm. Its carriers were found to be hole-like with charge carrier mobility of μ = 7.76 × 10^-2 cm²/Vs. For the SWNT-rope, the temperature-dependence of resistivity exhibited signatures of a Luttinger liquid for temperatures below 30 K. With varying gate voltage, periodic peaks were seen in the nanotube current which would normally be attributed to the effects of Coulomb blockade. Interestingly, these peaks show three-way splitting, similar to observations in triple quantum dot experiments. The MEH-PPV stripe, which was produced using electron beam lithography, had I-V characteristics similar to that of a large band-gap semiconductor. In the high field region, these characteristics could be explained in terms of a single carrier device model which considers the field-dependent mobility along with space charge limited conduction (SCLC). All three samples can be considered as field-effect transistors (FETs), with potential use in future high density integrated electronic devices.