Metal-Molecule-Metal Junctions on Self-Assembled Monolayers Made with Selective Electroless Deposition

Electronic transport through molecular-scale devices has been studied extensively for its extraordinary dimension superiority. Assembling such devices into large-scale functional circuits is crucial since the molecular tunnel junctions must be reliable, stable and reproducible during technological applications. In ideal circumstances, the device architecture should be designed such that the metal-molecule-metal (MMM) junctions can be analyzed by the more sensitive four point probe system. In this paper, we expound a delicate method to manufacture molecular junctions, which show excellent stability and reproducibility with high yields (>91 per cent). We form self-assembled monolayers (SAMs) on conductive Au thin film by microcontact printing and then generate robust covalently bound metal thin film electrodes on top of the SAMs by selective electroless deposition. Following MMM junction formation, a photoresist is coated and wells are opened on each feature by lithography. Then, Au thin film, as a permanent top electrode, is deposited into the photolithographically defined well. Conductivity analyzations were carried out on the 50 μm square junctions by the four point probe measurement, and the results showed reproducible tunneling I-V characteristics. This method reveals an approach not only offering a unique vehicle to investigate the electrical properties of molecule ensembles in MMMs, but also making a significant step toward MMM applications at the device level.