Odd‐even effects in molecular junctions: A Solomonic resolution of conflicting reports on conductance trends, metal specificity, and microscopic origin

Abstract Odd–even conductance alternation in alkanethiol (CnT, –12) self‐assembled monolayers has been debated for two decades, with conflicting reports on trends, metal dependence, and microscopic origin. Using conducting probe atomic force microscopy (CP‐AFM) with Ag, Au, and Pt electrodes, we extract low‐bias conductance and effective molecule–electrode coupling via the off‐resonant single‐level model, combined with rigorous ‐score statistics (Welch's ‐test for unequal variances). We present a Solomonic resolution—meaning a balanced compromise that recognizes truth on both sides—to these long‐standing controversies. First, the odd–even effect has a dual origin, manifesting in both the contact conductance prefactor (, ) and the length‐decay constant (, ). Interface and bulk contributions are therefore not mutually exclusive. The assignment to interface versus bulk remains inferential from transport parameters; independent structural characterization would be desirable but faces substantial experimental challenges. Second, the relative conductance of odd versus even chains reverses with length: odd chains are more conductive at short lengths, while even chains become superior beyond a crossover. A point estimate near –13 emerges from the global fits, yet the limited experimental window (–12) and the small difference in decay constants produce a wide uncertainty interval; the precise location of the crossover therefore remains undetermined. The qualitative inversion itself (from to ), however, is a robust finding and offers a natural reconciliation of prior opposing claims. Third, the effect is observed in CP‐AFM junctions under the present experimental conditions. Earlier CP‐AFM analyses of CnT junctions did not report it because they employed parity‐agnostic fitting; once the data are deliberately split by parity the effect becomes statistically clear. Fourth, metal dependence follows parity‐insensitive work‐function scaling with . Paradoxically, although absolute odd–even differences are smallest on Ag (conductances ∼20 times lower than on Au), statistical confidence is highest for Ag ( %), owing to exceptional reproducibility of even‐chain data. This analysis demonstrates that “weaker” does not imply “absent” and highlights the necessity of variance‐aware statistics. Apparently contradictory literature findings arise from different regimes of a single underlying phenomenon.