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 co ntacted to four-probe electrodes, with 100-nm spacing and various electroni c transport properties such as the I-V characteristics, the temperature dep endence of resistivity and the gate voltage dependence of the transport cur rent were measured. The PA nanofiber was found to be non-ohmic with a room temperature conductivity of similar to 0.1 S/cm.. Its carriers were found t o be hole-like with charge carrier mobility of mu = 7.76 x 10(-2) cm(2)/Vs. For the SWNT-rope, the temperature-dependence of resistivity exhibited sig natures of a Luttinger liquid for temperatures below 30 K. With varying gat e voltage, periodic peaks were seen in the nanotube current which would nor mally be attributed to the effects of Coulomb blockade. Interestingly, thes e peaks show three-way splitting, similar to observations in triple quantum dot experiments. The MEH-PPV stripe, which was produced using electron bea m lithography, had I-V characteristics similar to that of a large band-gap semiconductor. In the high field region, these characteristics could be exp lained in terms of a single carrier device model which considers the field- dependent mobility along with space charge limited conduction (SCLC). All t hree samples can be considered as field-effect transistors (FETs), with pot ential use in future high density integrated electronic devices. (C) 2001 E lsevier Science B.V. All rights reserved.