Investigation of interparticle interactions of larger (4.63 nm) monolayer protected gold clusters during quantized double layer charging.

In this article, the effect of interparticle interactions of 4.63 nm sized monolayer protected gold clusters (Au MPCs) during quantized double layer (QDL) charging has been investigated using electrochemical techniques. Voltammetry and scanning tunneling microscopy have been used to compare their electron transfer behavior. Furthermore, since the QDL process is diffusion controlled, the diffusion coefficient values have been estimated at various charge steps using two independent electroanalytical techniques, viz. chronoamperometry and impedance. These results show that higher core charge facilitates higher diffusion coefficient values, and indicate that repulsive interactions dominate for charged MPCs compared to those of its neutral analogue, which are mainly attractive in nature. Additionally, the electron transfer rate constants at various charge steps have been estimated from the impedance results, showing comparatively faster electron transfer rate at higher charge states.

Temperature-induced phase transitions of the ordered superlattice assembly of Au nanoclusters.

Superlattices of monolayer protected metallic and semiconducting nanoclusters have attracted significant attention due to their promising applications in nanotechnology. In this paper, we investigate the effect of temperature on the ordered superlattice structure of relatively larger sized Au nanoclusters passivated with dodecanethiol [ca. Au1415(RS)328] with the help of in situ temperature controlled X-ray diffraction (XRD) and infrared spectroscopy (IR) in conjunction with thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis. In brief, monolayer protected Au nanoclusters (AuMPC) were prepared by a modified Brust synthesis technique, where dodecanethiol itself acts as both phase transfer and simultaneous capping agent during the reduction process, generating an average particle size of 3.72 +/- 0.4 nm after repeated solvent extraction and careful fractionation experiments. These particles are characterized with the help of UV-vis, transmission electron microscopic (TEM), IR, and NMR techniques, where effective capping as well as the superlattice formation on the TEM grid is evident from the combined analysis of these results. In situ low-angle XRD analysis shows that the particles undergo an irreversible phase transition in the temperature range of 100-115 degrees C, which is also reflected in the data from in situ IR analysis. However, the DSC analysis does not account for this phase transition, although the reversible phase transition due to the alkyl chain dynamics is in good agreement with the previously reported results. These results indicate the formation of temperature-induced, diffusion-limited phase transition involving nonequilibrium fractal structures, which is in good agreement with the previous available theoretical studies. The determination of the temperature window for the stability of these ordered assemblies would be used to understand the effect of thermal stress for device applications.