Ag@Au core-shell nanoparticles were synthesized via chemical liquid phase reduction method.They were characterized by UV-Vis absorption spectroscopy

transmission electron microscopy(TEM)

differential scanning calorimetry(DSC) and X-ray absorption fine structure(XAFS) spectroscopy.The Ag@Au nanoparticles are of uniform and stable monodisperse

with an average size of the Ag core of about 8 nm

and the Au shell thickness of about 3.5 nm.DSC spectra show that core-shell particles are the most dramatic diffusion in the alloying process around 300°C

and the alloy is completely formed at 500°C.From the high temperature in-situ XAFS and the RSF curves

significant changes are clearly seen in the local structure of Au atoms in the alloying process.By fitting the data with replacement method

the Au-Au bond length gradually becomes longer from 2.86 to 2.89 and the coordination bond from 8.0 to 6.1

with 2.1 Au-Ag coordination bonds and increased degree of disorder

at the alloy formation.The alloy process is mainly based on subrogation diffusion.