We have studied the electrical conductivity in monolayer films of an ionic disk-shaped liquid-crystal molecule, pyridinium tethered with hexaalkoxytriphenylene (PyTp), and its complex with DNA by current-sensing atomic force microscopy (CS-AFM). The pure PyTp and PyTp-DNA complex monolayer films were first formed at the air-water interface and then transferred onto conducting substrates by the Langmuir-Blodgett (LB) technique to study the nanoscale electron transport through these films. The conductive tip of CS-AFM, the LB film, and the metal substrate form a nanoscopic metal-LB film-metal $\left(M\text{−}\mathrm{LB}\text{−}M\right)$ junction. We have measured the current-voltage $\left(I\text{−}V\right)$ characteristics for the $M\text{−}\mathrm{LB}\text{−}M$ junction using CS-AFM and have analyzed the data quantitatively. We find that the $I\text{−}V$ curves fit well to the Fowler-Nordheim (FN) model, suggesting electron tunneling to be a possible mechanism for electron transport in our system. Further, analysis of the $I\text{−}V$ curves based on the FN model yields the barrier heights of PyTp-DNA complex and pure PyTp films. Electron transport studies of films of ionic disk-shaped liquid-crystal molecules and their complex with DNA are important from the point of view of their applications in organic electronics.

• Received 4 April 2008

DOI:https://doi.org/10.1103/PhysRevE.78.021606