Organization of Nanoparticles in Solution-A TEM Study

Abstract: A new approach to the study of nanoparticle systems has been introduced. Nanoparticle systems in aqueous and organic solutions have been synthesized and studied by transmission electron microscopy. These systems include nanoparticles of gold, silver, palladium, ruthenium, and platinum which have been stabilized using various ligands. The particles were initially studied as deposited samples on carbon film by traditional transmission electron microscopy. It was observed that this type of sample preparation introduces artifacts due to the hydrodynamic effects in the solvent and interactions with the substrate upon drying. A specific sample preparation method, plunge-freezing, was used in order to produce samples representative of the state of aggregation of the particles in solution. This sample preparation, which was previously mainly used on aqueous samples, has been adapted to organic solvent-based samples. Differences in electron beam sensitivity were noted between different solvents. Observation of nanoparticle systems with this method allowed evidencing the presence of ordered aggregates of particles already in solution. These structures appear to be equilibrium structures. One specific ligand allowed the formation of interfacial films of nanoparticles between an aqueous phase and an organic phase. Using the plunge freezing technique, these films could be determined to be organized monolayers of particles, with some defects present. The compatibility of this technique with energy-filtered imaging was demonstrated on bimetallic systems. High resolution capability of this technique was also demonstrated by recording images with structural resolution of better than 2 Ångström.