Structural and optical properties of Ag: TiO2 nanocomposite films prepared by magnetron sputtering

Three sets of nanocomposite films consisting of different atomic concentrations of Ag dispersed in a TiO2 dielectric matrix were deposited by DC reactive magnetron sputtering, and subjected to several thermal annealing experiments in vacuum, for temperatures ranging from 200 to 600 ºC. The main goal of the present study is to analyse the optical properties of the as-deposited and annealed films in order to clarify the role of Ag inclusions in the TiO2 dielectric matrix. The influence of the thermal annealing in the structural and morphological evolution was then correlated with the changes in the optical behavior of the samples. Significant structural and morphological changes were observed, consisting on the crystallization of Ag and their clustering. Clusters growth as a function of temperature was also observed by the evolution of the diffractograms with the temperature increase. The present study allowed to conclude that at certain concentrations (close to 10 at. %), the films revealed some important changes on the optical properties, commonly known as Surface Plasmon Resonance, SPR. This change in the optical behavior of the films was found to be in accordance with the clusters growth as concluded from the evolution of the diffraction patterns. The optical changes, and the correspondent Surface Plasmon Resonance effect were confirmed by reflectivity and CIELab colour measurements. The samples with lower Ag content (11 at. % and 7 at. %) show typical interferometric behavior on the reflectivity curves, similar to those of “pure” TiO2 samples. After a minimum of reflectance at 300 nm, there was an increase of the reflectivity at higher wavelengths. For the samples annealed between 400 and 600 °C, a red-shift centered at around 500-550 nm is visible in the absorbance spectrum.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/ 70037/2006