Electrical characteristics of conjugated self-assembled monolayers in large-area molecular junctions

We have studied the electrical characteristics of close-packed monolayers of conjugated para-phenylene oligomers as a function of molecular length in large-area molecular junctions. An exponential increase in resistance with molecular length is observed, R∝exp(βL), with β=0.26±0.04 Å−1 and β=0.20±0.06 Å−1 for dithiol and monothiol derivatives, respectively. The decay coefficients are lower than previously determined experimentally using scanning probe or breakjunction techniques. We tentatively explain the low values by the forced planer geometry of the self-assembled molecules.