Formation of silver nanoparticles and self-assembled two-dimensional ordered superlattice

1-Nonanethiol-capped silver nanoparticles of about 4.18 nm in diameter were prepared using a liquid-liquid two-phase method. Two-dimensional ordered superlattices of the nanoparticles were formed on carbon films coated on transmission electron microscopy (TEM) copper grids by evaporating a drop of the dispersion in chloroform. The formation process of the silver nanoparticles was investigated by UV-visible absorption spectroscopy and TEM. A blue shift of the maximum absorption peak position of the UV-vis spectra occurred at the beginning of the reaction, followed by a red shift. This result indicated that large thiol-capped silver nanoparticles were formed at the beginning, then the large particles were decomposed into small particles, and in the final stage the small particles enlarged slightly again. The TEM images show directly the same process with the results from the UV-vis spectra. In addition, the W-visible spectra of the silver nanoparticle colloidal phase obtained finally show that the system is monodisperse and can remain stable for several weeks.