Core-shell Au/Ag nanoparticles were prepared by deposition of Ag through chemical reduction in the presence of preformed Au nanoparticles. By changing the molar ratio of Ag to Au, the thickness of the shell and thus the size of bimetallic particles could be controlled in convenient way. In this work, uniformly-sized core-shell Au/Ag nanoparticles were prepared with large amounts of depositing metals until the molar ratio of Ag to Au reaches 1:10. The formation mechanism of the "core-shell" type nanoparticles was studied by UV-vis spectra, transmission electron microscopy (TEM), etc. A small moiety of silver ions on the surface of gold seeds is reduced. The remaining silver ions in solution are reduced to form nanoclusters. The clusters are deposited on the surface of the particles and the thickness of silver shells increased.

Key words: GOLD, SILVER, NANOPHASE MATERIALS, UV, TEM, OPTICAL PROPERTIES