Fabrication of Stable Molecular Electrode Using Patterned Edge of a Metal/Insulator/Metal Junction

A novel molecular electrode utilizing the exposed-vertical edge of a metal-insulator-metal tunnel junction has been successfully fabricated. Molecular metal clusters possessing thiolacetate terminated tether ligands were electrochemically bonded with metal layers resulting in the molecule spanning across the insulating film (Al2O3, 2nm thick). The molecule then became the dominant current path as confirmed by transport measurement. The success of the molecular electrode depended strongly upon the ability of insulating film to withstand morphological changes produced by the mechanical stresses incorporated during the sputtering film deposition process. Time evolution of stresses and corresponding formation of hillocks that produce shorts between metal films of tunnel junction electrodes are described. A new method, using multistep Al deposition and oxidation for alumina growth, was developed to form a mechanically robust tunnel insulator layer. Reliable electrodes with gap widths having angstrom level precision have broad application in the development of molecular electronics.