Ruthenium Nanoparticles Stabilized by the Self-Assembly of Acetylene, Carboxylate, and Thiol Derivatives

Stable ruthenium nanoparticles capped with three kinds of organic ligands, 1-dodecyne, sodium laurate and 1-dodecanethiol were synthesized by the self-assembly of these ligands onto ruthenium colloids produced by a simple thermolytic method, forming ruthenium-vinylidene (Ru=C=CH), -oxygen (Ru-O), and -thiolate (Ru-S) interfacial bonds, respectively. Transmission electron microscopic studies showed the nanoparticle core diameter was around 2 nm. FTIR, TGA, and XPS measurements confirmed the attachments of the organic ligands onto the ruthenium particle surface, and the polarization of the interfacial bonds was found to increase in the order of Ru=C=CH- < Ru-S < Ru-O. The electron-transfer properties of the resulting nanoparticles were then examined by scanning tunneling spectroscopic (STS) measurements, where relatively large nanoparticles (dia. similar to 3 nm) were found to show clearly-defined Coulomb staircase; and with diminishing particle core dimensions to below 1 nm, Coulomb blockade started to emerge. On the basis of the current potential profiles, the nanoparticle molecular capacitance and hence the effective nanoparticle dielectric constants were estimated. It was found that for all samples the dielectric constants increased inversely with the nanoparticle core dimensions; and at any given particle size, the dielectric constants varied with the specific metal-ligand interfacial bonds, increasing in the order of Ru-S < Ru=C=CH < Ru-O. The results further highlight the significance of metal-ligand interfacial bonds in controlling the nanoparticle material properties.