Transport studies of isolated molecular wires in self-assembled monolayer devices

We have fabricated a variety of isolated molecule diodes based on self-assembled monolayers (SAM) of solid-state mixture (SSM) of molecular wires [1,4-methane benzene dithiol (Me-BDT)], and molecular insulator spacers [penthane 1-thiol (PT)] with different concentration ratios r of wires/spacers, which were sandwiched between two gold (Au) electrodes. We introduce two specialized methods borrowed from surface science to (ii) confirm the connectivity between the Me-BDT molecules with the upper Au electrode, and (ii) count the number of isolated molecular wires in the devices. The electrical transport properties of the SSM SAM diodes were studied at different temperatures via the conductance and differential conductance spectra. We found that a potential barrier caused by the spatial connectivity gap between the PT molecules and the upper Au electrode dominates the transport properties of the pure PT SAM diode (r=0). The transport properties of SSM diodes with r values in the range 10−8<r<10−4 are dominated by the conductance of the isolated Me-BDT molecules in the device.