Load-Free Determination of Film Structure Dependent Tunneling Decay Factors in Molecular Junctions

Two supramolecular orders of alkanethiol molecules self-assembled on Au(111) differing in molecular tilt angles, molecular density, and in-plane order are investigated, for a variety of chain lengths, by means of conductive scanning force microscopy. A load-free approach is presented as an alternative to the common pressure-induced methods used for investigating electron transport mechanisms in these films. The methodology, which compares molecular junctions with different thickness but exactly the same number of through bond channels, allows analyzing the molecular tilt influence (e.g., through space probability) on the current response while avoiding pressure-induced defects or film restructuring under pressure. In addition, it constitutes a direct strategy that has permitted us to evaluate tunneling decay factors which are specific of the supramolecular order within the film.