c © TÜB_ITAK Au Nanoparticle Clusters: A New System to Model Hopping Conduction

We study electrical transport through self-assembled Au nanoparticle clusters which can be viewed as a new model system to study hopping transport. The physics of such systems is governed by two parameters: the charging energy and tunnel coupling between the particles. The charging energy is determined by the size of the nanoparticles. When the diameter of the nanoparticles is less than 4-5 nm the charging energy is large enough that Coulomb blockade eects were observed in electri-cal transport even at room temperature. The magnitude of the tunnel coupling between the parti-cles was determined by the thiol coating used. To study a wide range of tunnel couplings, we have synthesized gold nanoparticles with various thiol coatings, including 1-octanethiol, 1-dodecanethiol, 1-octadecanethiol, 4-mercaptodiphenylacetylene, 4-nitro-4-mercaptodiphenylacetylene, and 3,5-dinitro-4-mercaptodiphenylacetylene. Current-voltage characteristics were found to be strongly dependent on both the coating and the size of the nanoparticles. At low temperature we have observed nonlinear I-V characteristics with a threshold voltage that was signicantly larger in gold nanoparticle clusters where the thiol coating had weak tunnel coupling. Key Words: nanoparticles, Coulomb blockade, hopping conduction. 1