Effects of Metal-Ion Complexation for the Self-Assembled Nanocomposite Films Composed of Gold Nanoparticles and 3,8-Bis(terthiophenyl)phenanthroline-Based Dithiols Bridging 1 fim Gap Gold Electrodes: Morphology, Temperature Dependent Electronic conduction and photoresponse.

摘要

3,8-Bis(3',4'-dibutyl-5"-mercapto-2,2':5',2"-terthiophen-5-yl)-1,10-phenanthroline (2) with a molecular length of 3.36 nm and its Ru(II), Fe(II), and Cu(II) complexes were treated with tert-dodecanethiol-protected active gold nanoparticles (Au-NPs) in an average size of 3.3 nm in the presence of two facing Au electrodes with a 1 x 1 μm~2 gap. Stable self-assembled molecular junctions were produced, wherein dithiols-bridged Au-NPs were chemisorbed to the electrodes by means of Au—S-bonded contacts. SEM and AFM micrographs showed that different morphologies of the films were formed depending on the number of ligand 2 in the molecules and the coordination configurations of transition metal ions. Among them a relatively homogeneous granular thin film was obtained successfully in the case of the [Ru(bpy)2]~(2+) complex. Temperature-dependent current—voltage measurements for these junctions were performed in the temperature range of 8—300 K. The electronic conduction is dominated by the sum of tunneling and thermal excitation. Classical Arrhenius plots and their linear fits, wherein the temperature-independent tunneling current was deducted, were obtained to determine the average activation energies of these nanodevices. Photoresponsive properties of these self-assembled films were studied at different temperature (80, 160, and 300 K, respectively), where reversible and reproducible photoresponse can be recorded at room temperature in the presence of [Ru(bpy)2]~(2+) species. The comparison of results before and after metal—ion complexation reveals that the introduction of Ru(II) ion into the metal—molecule system can improve effectively the morphology of the self-assembled films and the overall conductivity, decrease the barrier for activation energy, and enhance the photoresponse of these nanodevices.