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 tetraoctyl-ammonium 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.