Optical properties of cobalt clusters implanted in thin silica layers

Abstract

We present an optical characterization of cobalt nanostructured silica thin layers. Cobalt clusters in the size range 4 -8 nm are obtained after implantation of Co + ions into 200-nm-thick silica ͑SiO 2 ͒ layers on c-oriented silicon substrate ͑Si͒. Implantation has been performed for substrate temperatures of 295 K ͑Room Temperature͒ and 600°C. Spectroscopic ellipsometry measurements have been carried out on the 350-850 nm spectral range. Different simulation models have been developed to understand optical responses of these layers. We investigate all effects that can have an influence on the optical responses such as sample structure, size effects, defects of silica, and oxided particles. We show that the samples can be correctly modelled by considering the layers as a homogeneous mixture of cobalt clusters and silica buried into silica. Such a mixture is perfectly characterized by the Maxwell-Garnett cermet topology dielectric function. Additional Rutherford backscattering measurements have been carried out to question optical results and show the reliability of the ellipsometric approach.

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