Relation between the optical properties of composite Si3N4 thin films withembedded Cu clusters and the clusters morphology: Irradiation effects

Ion beam sputtering codeposition has been used to elaborate ceramic-metal ( cermet) composite thin films consisting of copper nanoclusters embedded in an amorphous Si3N4 matrix. As prepared, the clusters have a size smaller th an 3 nm and postirradiation by high energetic Ar+ ions leads to an homogeni zation of the clusters' morphology and an increase of the clusters' size to an average diameter of 4.5 nm. This work deals with the relation between t he morphology of the clusters, characterized by extended x-ray absorption f ine spectroscopy and grazing incidence small angle x-ray scattering, and th e optical properties (obtained by spectroscopic ellipsometry) of the cermet s, which are classically modeled with the help of the effective medium theo ry. In the case of the as-prepared sample, the Bruggeman effective medium t heory has been successfully used. This comes from the fact that the cluster s are sufficiently close to each other to create mutual interactions. On th e other hand, the morphology of the postirradiated film is in agreement wit h the hypothesis made by the Maxwell-Garnett effective medium theory, and a resonance peak appears due to the surface plasmon excitation whose positio n depends on the cluster size. (C) 2001 American Institute of Physics.