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 s uperlattices of the nanoparticles were formed on carbon films coated on tra nsmission electron microscopy (TEM) copper grids by evaporating a drop of t he dispersion in chloroform. The formation process of the silver nanopartic les was investigated by UV-visible absorption spectroscopy and TEM. A blue shift of the maximum absorption peak position of the UV-vis spectra occurre d at the beginning of the reaction, followed by a red shift. This result in dicated that large thiol-capped silver nanoparticles were formed at the beg inning, then the large particles were decomposed into small particles, and in the final stage the small particles enlarged slightly again. The TEM ima ges show directly the same process with the results from the UV-vis spectra . In addition, the W-visible spectra of the silver nanoparticle colloidal p hase obtained finally show that the system is monodisperse and can remain s table for several weeks.