Binary clusters: homogeneous alloys and nucleus-shell structures

Extinction spectra of Ag_x-Au_(1?x)-alloy particles embedded in glass are compared to spectra of gold coated silver clusters and silver coated gold clusters. It is shown, that the optical extinction of alloy particles is described by the Mie theory applying the homogeneous dielectric function (hat varepsilon ) (ω,R, x) measured by Paquet. The absorption of core-shell clusters was calculated deriving an extension of the Mie theory to spheres with arbitrary numbers of shells of arbitrary materials. Comparison to measured spectra points to s-electron motion in the clusters with only slight scattering at the interior interface. The appearance of two distinct Mie peaks however proves the existence of the sharp Ag-Au interface. The extended Mie formalism was also applied to a multilayer system consisting of sodium and a dielectric substance as an example for a spherical hetero structure.