Optical properties of mixed clusters: comparative study of Ni/Ag and Pt/Ag clusters
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The optical properties of mixed (Ni0.5Ag0.5)n and Pt/Ag clusters are investigated in the size range 2-5 nm. Low Energy Ion Spectroscopy (LEIS) experiments show that the cluster surface is entirely covered by silver atoms for the two systems. The optical spectra of Ni/Ag clusters exhibit a large Surface Plasmon Resonance (SPR), damped and widened when the cluster size decreases, in agreement with a classical model assuming a core-shell geometry and including the reduction of the conduction electron mean-free path in the silver shell. For Pt/Ag clusters, no SPR emerges in the size range 2-5 nm, although it is predicted within a classical model, a pronounced SPR appearing only for clusters larger than 10 nm in diameter.
PACS.36.40.Vz Optical properties of clusters 36.40.-c Atomic and molecular clusters 78.66.Bz Metals and metallic alloys
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