Dipole-induced asymmetric conduction in tunneling junctions comprising self-assembled monolayers

This paper describes the observation of asymmetric conductance in the form of differing ratios of current density (J) as a function of voltage (|V|) in tunneling junctions comprising self-assembled monolayers on gold using eutectic Ga–In as a top contact. Monolayers comprising compounds with nearly identical physical and electronic properties show opposite directions of this asymmetry. We tested the statistical significance of the effect and ascribed it to the collective action of embedded dipoles arising from pyrimidyl groups that are arranged parallel or antiparallel to the transport direction. We ascribe the effect to the bias-induced (de)localization of the frontier states that mitigate transport.