Optical properties of nanostructured thin films containing noble metal clusters: Au-N, (Au0.5Ag0.5)(N) and Ag-N

The optical properties of nanocomposite thin films of gold, silver and bime tallic silver-gold clusters embedded in a porous alumina matrix have been i nvestigated in the size range 2-6.7 nm. The metallic particles are produced by laser vaporization of either an Au0.5Ag0.5 alloy or a pure metal target whereas the dielectric matrix is evaporated by an electron gun. Samples in volving a low metal concentration have been characterized by several comple mentary techniques in order to determine their composition, morphology and cluster size distribution. The mixed particles have the same stoichiometry as the target rod. Optical absorption spectra exhibit a surface plasmon res onance whose position is shifting with cluster mean size, giving evidence o f finite size effects. Theoretical calculations in the framework of Time-De pendent-Local-Density-Approximation (TDLDA), taking into account an inner s kin of ineffective screening and the porosity of the matrix, are consistent with observed size evolutions of the Mie frequency in each type of sample. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All right s reserved.