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Propriétés optiques d'agrégats mixtes de métaux de transition en matrice d'alumine : Effets de taille et de composition

Abstract : Optical response of small noble metallic particles (Au, Ag, Cu) is dominated by a Surface Plasmon Resonance band whose position and width depend mostly on their size and on the surrounding material. This manuscript presents the study of the optical properties of bi-metallic clusters AuM (M=Ag, Ni, Co et Pt) in the diameter range 1.5-6 nm, embedded in alumina. The sample preparation and different characterisation techniques are first described. Then theoretical models are introduced to interpret optical properties. A semi-quantical approach introduces core electrons, matrix and porosity of the matrix influences, but is not really suited for all the metals studied here. In other cases, a classical model is used. The third part emphasizes the size and composition effects on the optical properties of mixed AuAg clusters. For a given relative composition, the blueshift, damping and broadening of the resonance are all the more important as the size decreases, and as the gold concentration increases. These spectra are compared with semi-quantical model calculations, based on the TDLDA formalism, including both the porosity of the matrix and an inner skin with a reduced ionic-core polarizability. Two models are introduced to describe the effective dielectric function of the ionic background in the bi-metallic clusters. We can conclude that we study alloyed AuAg clusters. At last, NiAg and CoAg are formed by a nickel or cobalt-core surrounding by a silver-shell. As predicted theoretically by classical calculations, absorption spectra present a plasmon resonance band, and, for Ni-Ag, this band actually evolves continuously from the silver one to nickel one as the nickel proportion increases. Experimentally, the plasmon band for PtAg clusters is strongly lightened which is not predicted by classical calculations neither when the dielectric function is simply expressed through those of its constituents, nor for a core-shell.
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Contributor : Mélanie Gaudry <>
Submitted on : Friday, July 26, 2002 - 3:08:54 PM
Last modification on : Thursday, October 15, 2020 - 9:00:22 AM
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Mélanie Gaudry. Propriétés optiques d'agrégats mixtes de métaux de transition en matrice d'alumine : Effets de taille et de composition. Physique [physics]. Université Claude Bernard - Lyon I, 2002. Français. ⟨tel-00001513⟩

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