(35g) Electric Field Driven Assembly and Temperature Dependent Conduction through Nanoparticle-Molecule-Nanoparticle Structures
Understanding conduction mechanisms through a single molecule remains a critical question in molecular electronics. Particular difficulties are related to the instability of metal-molecule contacts and possible interactions between multiple molecules in the junction. Here we report fabrication of unique nanoparticle/molecule/nanoparticle bridge structures consisting of ~40nm gold nanoparticles linked by a phenylacetylene oligomer molecule. We also describe methods to achieve electrical contact to these structures across nanoscale (~70nm) conducting electrodes fabricated by a simple angled metal evaporation method. The assembly of the nanoparticle/molecule structure onto nanoscale electrodes is performed by dielectrophoretic trapping. At the optimum trapping conditions (2VAC, 1MHz, and 60s) a success rate of ~78% is achieved, allowing direct characterization of electrical contact and charge transport. Current versus voltage through the nanoparticle/molecule structure is consistent with a single molecule present between the nanoparticles, and IV results are obtained as a function of temperature and time in ambient. Contacts are observed to be highly stable in vacuum, but conduction is observed to slowly increase by a factor of 10 over time (1-2 weeks) upon exposure to ambient air, consistent with modifications in contact properties. Fitting of the IV data to charge tunneling models will also be presented and discussed.