Irrelevant Role of Level-Electrode Coupling Asymmetry in Driving Rectification in Molecular Tunnel Junctions: Decisive Experimental Evidence from Junctions with Dissimilar Electrodes.

Current rectification in molecular junctions inherently requires broken forward-backward symmetry. A key question is whether asymmetric electrode-molecule coupling significantly drives rectification in practical molecular electronics. To address this, previously explored only theoretically, we used conducting probe atomic force microscopy (CP-AFM) to fabricate molecular junctions with symmetric molecules and dissimilar electrodes (Ag, Au, Pt). Using complementary benchmark molecular systems-saturated alkyl chains (featuring localized electrons) and oligophenyls (with delocalized electrons), we demonstrate that metal-molecule contact asymmetry does not significantly contribute to rectification, thereby discarding a theoretical formula that has retained undue consideration in the molecular electronics community and continues to be presented as an open question under debate. This assumption-free experimental finding provides crucial guidance for rationally designing high-performance molecular rectifiers.