Dodecanethiol-Derivatized Au/Ag Bimetallic Nanoparticles: TEM, UV/VIS, XPS, and FTIR Analysis

Dodecanethiol-derivatized Au/Ag bimetallic nanoparticles that can be dissolved in nonpolar solvents were prepared via a two-phase synthetic route in water/toluene mixtures. The position of the surface plasmon band was found to vary linearly between 419 and 522 nm as a function of mole fraction of Au (or Ag) content, implying ready formation of Au-Ag alloy clusters. Transmission electron microscopy images revealed that the bimetallic clusters were monodisperse with an average size of approximately 4 nm. Infrared spectral features indicate that the alkyl chains of the dodecanethiolate species take fully extended trans zigzag conformations on all alloy clusters. The most interesting finding deduced from X-ray photoelectron spectroscopy and FTIR spectroscopic measurements was that Ag atoms are enriched at the outer part of the alloy clusters when compared with the Au atoms. Copyright 1998 Academic Press.