Ferrocene-based molecular electronics and nanomanufacturing of Pd nanowires.

Abstract

Two test structures were tried out for molecular junction formation and subsequent I-V characteristics measurements. One is formed by insertion of certain dithiol molecules into an alkanethiol self-assembled monolayer (SAM), followed by tethering the free thiol end with gold nanoparticles. The test structure can then be measured with CP-AFM. The matrix SAM, mixed monolayer with inserted dithiol molecules, and final test structure with gold nanoparticles were prepared and characterized by ellipsometry, AFM and STM. However, the CP-AFM measurements were very irreproducible, even on an alkanethiol SAM. This problem was analyzed and believed to come from two possible causes, namely thermal drift and deformation of the metalized tips. The other test structure was from insertion of molecules into nanogaps made by electromigration technique. Two molecules were tested and drastically different properties were observed from junctions with each molecule. For Fc-OPE molecules, near perfect conductance peaks (>0.6G0) were observed in some junctions and analysis indicates that such molecular junction contains only one or two molecules inside the nanogap. The formation of conductance peaks was analyzed with Landauer formula and a simple metal-molecule-metal model. Computational calculation also predicted high conductance through such junctions and the existence of resonant peaks. The junctions with OPE molecules, however, showed poor conductance. Possible causes such as molecular structure and easiness of molecular junction formation were discussed. In the second part of this dissertation, a new method was developed to fabricate Pd nanowires on HOPG surface using a sacrificial Cu film. The morphology and composition of the nanowires were characterized by AFM, SEM and XPS. The formation of such Pd nanowires was explained with a galvanic displacement mechanism and some test experiments were carried out to prove such growth mechanism. It was also found that the size of the Pd nanowires can be directly controlled by the thickness of the Cu film that was initially deposited. However, attempts to make Au, Pt and Ag nanowires with the same method failed, and possible causes were discussed.