Chemistry and Biochemistry

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 molecule