The Synthesizing And Characterizing Of Surface Modified Gold Nanoparticles On Self-Assembled Super Lattices

Surface modified Au nanoparticles have been synthesized based on the reduction of hydrogen tetrachloroaurate (HAuCl4) by sodium borohydride (NaBH^ in methanol. In solution-phase metal salt reduction, aggregation of reduced atoms or micro-clusters may give stable nuclei. The growth of nuclei to metal nanoparticles can proceed by deposition of atoms or micro-clusters on the surface of nuclei. A key step to control the size and shape of the growing particle is dynamically to coat the particles with a closed-packed monolayer of coordinating ligand, mercaptosuccinic acid (MSA). Suitable large size nanoparticles (several tens nanometer) and nanorods have been made.After size selection, a certain size nanoparticles were assembled into micrometer sizable super lattice crystal. The samples were characterized by X-ray diffraction(XRD), optical spectroscopy, transmission electron microscopy (TEM) and scanning tunneling microscopy (STM).As a result, a self-assembled monolayer (SAM) of MSA on the surface of fee Au particles was directly observed in atomic level. Two kinds of modification on the single particle's surfaced were discussed. They are completely compatible with other analysis methods. From the STM result and its discussion, it is interesting to compare with those two kinds of modified surface, which are in different MSA/Au ratio, giving clear difference between MSA assembles on Au bulk surface and on nanoparticles', and how the processes of the stabilization formed on the particles.