Binary Au/Pd core-shell nanoparticles () were fabricated using Nd:YAG pulsed laser ablation in reactive liquid environment of PdCl 2 .with the choice of six different concentration. XRD, TEM and UV-Vis spectrophotometry characterized the Au/Pd samples. XRD showed fcc PdO and Au and PdCl 2 were formed in laser ablation process. No diffraction peaks of well crystallized metallic Pd appeared in XRD patterns of samples, indicating the palladium phase might exist in an amorphous phase or in the form of very small cluster due to low Pd concentration. UV-Vis absorption spectra were used to study the optical properties of Au/Pd bimetallic nanoparticles. According these spectra all the curves exhibit one intense peak at around 530 nm which corresponds to the absorption due to the well-known surface plasmon resonance (SPR) of Au metallic . It was observed that normalized absorption increases with PdCl 2 concentration. We found the peaks intensity strongly depends on the concentration of PdCl 2 . According to UV-Vis data it was found that SPR peaks undergo a shift toward high wavelength upon aging. To confirm the presence of Pd in Au/Pd core-shell , a chemical analysis of these samples was performed using XPS. By this analys one can study structural and electronic properties of the bimetallic . Spectroscopy a decrease intensity of the Au4f spectrum with Pd concentration indicated the formation a shell in cases containing PdCl 2 solution. Also the intensity Au4d 5/2 peak reduced with increase Pd concentration and Pd3d peaks binding energy of 328-348 eV increased. The surface concentration ratio of Pd to Au at different condition have been estimated. This suggests that gold is the core of bimetallic structure and palladium is enriched on the surface. TEM revealed that the Au are spherical in shape and a thin Pd layer has been deposited. This images demonstrates that PdCl 2 concentration is an effective parameter to control the Pd shell thickness. We found with increasing Pd concentration the Pd thickness increases but the size of Au core decrease due to the in decrease Au concentration. Pd shell thickness for the smallest Pd concentration was 0.9 nm and enhance gradually to 6.25 nm for AuPd sample that contains major amount Pd concentration. For a sample certain it was observed that with decrease Au core size increase the Pd shell thickness that this may be due to increasing surface activity with decrease of nanoparticle size, therefore Au nanoparticles have more tendency for synthesis by Pd atoms.
