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Compositional Inhomogeneity of Pd70Ag30 Alloy Nanoparticles Studied by XANES

Kuan-Wen Wang, Shu-Ru Chung, Ling-Yun Jang, Jyh-Fu Lee, and Tsong P. Perng
National Tsing Hua University, TW

Keywords: nanoparticle, XANES, Pd-Ag, surface modification

The compositional inhomogeneity of Pd70Ag30 nanoparticles with the size of 6-7nm was studied by X-ray absorption near edge structure (XANES). The composition of the as-prepared nanoparticles by chemical reduction is inhomogeneous across the diameter due to different reduction potentials of Ag and Pd [1-3]. During the heat treatment, Ag will migrate to the surface because of its lower surface energy. The composition is also affected by surface modification since it may change the surface energy during the oxidation and sintering processes. According to the ESCA results, surface modification on Pd70Ag30 nanoparticles (PdAg-p) by polyethylene glycol (PEG) will decrease the surface energy of Ag and assist the diffusion of Ag from the core to the surface. This makes the nanoparticles easier to sinter together because of the lower melting point of Ag. The results from XANES show that the L3 edge shift of Ag in PdAg-p is less than those in unmodified PdAg and PdAg modified by stearic acid (PdAg-sa). Because of the strong interaction between PEG and Ag in Pd70Ag30, desorption of oxygen from Ag is difficult and the edge shift is small at higher temperatures. For the particles of PdAg-sa, stearic acid may increase the surface energy of Ag and retard the diffusion of Ag from the core to the surface. Therefore, the oxygen desorption and edge shift are higher than those of PdAg-p. References: [1] H. C. Chu, S. R. Sheen, C. T. Yeh, and T. P. Perng, J. Alloys Comp., 322, 198 (2001). [2] C. U. Huang, H. J. Chiang, J. C. Huang, and S. R. Sheen, NanoStruct. Mater., 10, 1393 (1998). [3] C.-W. Chou, S.-J. Chu, H.-J. Chiang, C-Y. Huang, C.-J. Lee, S.-R. Sheen, T.-P. Perng, and C.-T. Yeh, J. Phys. Chem., B, 105, 9113 (2001)

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