Electron transport in networks of gold nanoparticles connected by oligothiophene molecular wires

Abstract

Network structures made of π-conjugated molecular wires of oligothiophene 3mer, or 9mer carrying thiol groups at α,ω-positions, and gold nanoparticles with average diameter of 4 nm were prepared on interdigitated gold electrodes. Observation of the resultant assemblies by means of FE-SEM and TEM revealed that the gold nanoparticles were connected by π-molecular wires to form a network. The networks exhibited thermally activated electron transport at room temperature with activation energies of 21and 45 meV for 3mer- and 9mer-networks, respectively, and these values were almost the same as those of networks connected with non-conjugated molecules having similar lengths. However, the activation energy became very small (∼0.1 meV) at temperatures lower than 30 K and non-linear current–voltage characteristics (I ∝ V3) appeared in π-conjugated networks at 4.2 K. These results suggest that the gold nanoparticles in the networks work as Coulomb islands and the temperature-independent behavior at lower temperatures can be interpreted in terms of a co-tunneling mechanism.