Abstract

Nanolayered systems composed of a gold film coated by a granular tin dioxide layer, and a silver film coated by a granular layer of titanium dioxide are fabricated by combined sputtering/sol-gel methods. The conditions of the sol-gel synthesis and the substrate materials were adjusted with a particular attention to the aggregation effects, especially in the case of the gold/tin dioxide system. The dielectric particles are uniformly distributed on the metal surfaces and the films are smooth (mean roughness less than 6 nm). The components of the nanolayered systems prepared in this work are found to be crystalline and the sputtered metal is preferentially oriented on the substrate. Because of the low-temperature sol-gel method used for the synthesis, especially small (4-5 nm) crystallites of titanium dioxide (anatase allotropic phase) have been found with a narrow size distribution. Size and intensity enhancement effects have been evidenced in both systems and studied by micro-Raman spectroscopy. A particular attention is paid in this work to the optical properties of the nanolayered composites with an emphasis on the surface plasmon resonance. The near-normal reflection spectra are measured and the effect of the dielectric coating on both the surface plasmon band of the noble metal and the band gap absorption of the dielectric are investigated. The effective-medium theory is used to calculate the reflection curves. The simulated curves show a qualitative agreement with the experimental spectra. The possibility to use these systems in sensing applications is discussed.