MESOSCALE SPHERICAL AND PLANAR ORGANIZATIONS OF GOLD NANOPARTICLES

We present a systematic investigation on the roles of some starting reagents commonly used in gold nanoparticle synthesis. Our results show that Au nanoparticles adsorbed with tetraoctylammonium bromide (TOAB) or TOAB and 1-dodecanethiol (DDT) can self-assemble into spherical aggregates in various hierarchical forms, such as discrete, linear, and two-dimensional arrays, without using any additional structural linkers. Interestingly, aged Au nanoparticles in different interconnected spherical aggregates are highly ordered, showing long-range lattice uniformity. On the basis of our substrate-dependent experiments, it has been revealed that the sphere formation, self-assembly, and crystallization of Au nanoparticles in the superlattice take place upon drying. A structural evolution of mesoscale spherical assemblies to planar organizations of Au nanoparticles has also been revealed in this work for the first time. In general, the Au nanoparticles are better shelled with TOAB than with DDT surfactant. The symmetrical organic shells of TOAB and its multi-chain structure are believed to be responsible for the high capacity of particle aggregation as well as for the long-range assembling order.

High Resolution Diffraction Imaging of Mercuric Iodide: Demonstration of the Necessity for Alternate Crystal Processing Techniques for Highly Purified Material

The overall crystalline lattice uniformity in recently available, highly purified mercuric iodide single crystals has been shown to be impacted by crystal handling techniques that were previously satisfactory. High resolution diffraction imaging of the surface regularity of crystals of various levels of purity and growth orientation shows: 1) that the newer materials have a generally lower level of precipitates, 2) that the incidence of these precipitates is now closely correlated with growth direction, and 3) that the deformation resistance and resulting sensitivity to crystal handling procedures are also closely correlated with these factors in this soft material.As a result, gentler cutting and polishing procedures have been developed and are shown to be effective in preserving overall lattice regularity in the new material. The polishing required to remove residual surface scratches affects the lattice orientation of the softer, precipitate-free regions, while not affecting those regions with detectible levels of precipitates. These results correlate closely with the electrical properties of devices made from these crystals.