Orientation-dependent conductance study of pentacene nanocrystals by conductive atomic force microscopy

Oriented pentacene nanocrystals with long molecular axis either parallel or perpendicular to a Au substrate were prepared on a bare Au surface or a self-assembled monolayer (SAM)-modified Au surface, respectively. The conductance across the differently oriented pentacene crystals were measured by conductive atomic force microscopy in a similar device configuration of Au/SAM/pentacene/Au-tip and Au/pentacene/SAM-modified-Au-tip, respectively. Rectifying current was observed depending on the location of the SAM in the device. With an average thickness of 50 nm, the conductance along the C-H . . . pi stacking direction (a-b plane) was nearly five orders of magnitude larger than along the layer direction (c axis). (C) 2008 American Institute of Physics.