Contact Architecture Controls Conductance in Monolayer Devices

The architecture of electrically contacting the self-assembled monolayer (SAM) of an organophosphonate has a profound effect on a device where the SAM serves as an intermolecular conductive channel in the plane of the substrate. Nanotransfer printing (nTP) enabled the construction of top-contact and bottom-contact architectures; contacts were composed of 13 nm thin metal films that were separated by a ca. 20 nm gap. Top-contact devices were fabricated by assembling the SAM across the entire surface of an insulating substrate and then applying the patterned metallic electrodes by nTP; bottom-contact ones were fabricated by nTP of the electrode pattern onto the substrate before the SAM was grown in the patterned nanogaps. SAMs were prepared from (9,10-di(naphthalen-2-yl)anthracen-2-yl)phosphonate; here, the naphthyl groups extend laterally from the anthracenylphosphonate backbone. Significantly, top-contact devices supported current that was about 3 orders of magnitude greater than that for comparable bottom-contact devices and that was at least 100,000 times greater than for a control device devoid of a SAM (at 0.5 V bias). These large differences in conductance between top- and bottom-contact architectures are discussed in consideration of differential contact-to-SAM geometries and, hence, resistances.