Enhancement of field emission transport by molecular tilt configuration in metal-molecule-metal junctions.

We studied the molecular configuration-dependent charge transport of alkyl metal-molecule-metal junctions using conducting atomic force microscopy (CAFM). The inflection point (or transition voltage V(T)) on the plot of ln(I/V(2)) versus 1/V shifted to a lower voltage with increasing CAFM tip-loading force and decreasing molecular length. Our results indicate that the reduction of gap distance by molecular tilt configuration enhances the transition of the electronic transport mechanism from direct tunneling to field emission transport through molecules. The obtained results are consistent with a barrier height decrease, as affected by the enhancement of the intermolecular chain-to-chain tunneling as molecular tilt, predicted by a multibarrier tunneling model.