Size and composition dependence in the optical properties of mixed (transition metal/noble metal) embedded clusters

摘要: Optical properties of mixed clusters Ni/Ag, Co/Ag, and Ni/Au 2-5 nm in diameter, produced by laser vaporization embedded an alumina matrix, are investigated. The first part is devoted to (Ni x Ag 1 - ) n whose photoabsorption spectra reveal a surface plasmon resonance, damped, broadened, blue-shifted as compared pure silver clusters. For given mean size, blueshift the resonance band well damping broadening with increasing nickel proportion observed, good qualitative agreement classical predictions, assuming Ni-core/Ag-shell geometry. This core-shell structure confirmed low energy ion spectroscopy measurements showing that cluster essentially composed silver. composition, size evolution consists decreasing whereas no clear shift noticed. Although including scattering limited free path contribution conduction electrons shell, account for effects, inhomogeneous effects (size, shape, local porosity) also contribute experiment. second concerns optical (Co 0 . 5 Au similar clusters, addition, weak size. As their do not display marked resonance. comparison model dependent constant gold or shell gives understanding these features two systems Co/Ag Ni/Au.