From single-molecule contacts to well-defined molecular ensemble contacts: Influence of intermolecular interactions onto the electronic transport

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In this project we will study the electronic transport properties of molecular ensemble junctions, in which small molecules are contacted to metal electrodes in a parallel arrangement. In most cases their transport properties cannot straightforwardly be deduced from those of single-molecule junctions of the same species. Possible reasons for this difference include intrinsic properties (molecular interactions) as well as extrinsic reasons, like differences in the contacts geometry on the molecular level. While several techniques have been developed that enable to study the transport through single molecules, both in a statistical manner and on an individual molecular basis, no really reliable, scalable, and versatile method for the study of the transport through small molecular ensembles does exist. This methodological lack hampers systematic studies of the intrinsic effects that have recently attracted much interest from the theoretical side. The interest is driven by the high application potential of small to medium size molecular ensembles in molecular electronics, because they are less prone to artefacts caused by individual atomic arrangements, have lower resistance as single-molecule junctions but still combine the advantages of very small size and rich functionality. The applicant DM recently developed new processes for the fabrication of molecular ensemble contacts in crossbar architecture, with junction areas ranging from approximately 50 nm x 50 nm to several hundred square micrometers. The techniques have been successfully applied for the formation of junctions of thin conducting and semiconducting polymer layers of several nanometer thickness. We propose to further develop the crossbar technique for the application of self-assembled monolayers of molecular species to be used in molecular electronics.