Fotossensibilizadores nanoestruturados por sistema camada por camada

Abstract

The search for materials that can be modified at molecular level has been the subject of several studies worldwide. Thus, the production techniques of thin films stand out due to the possibility of reducing costs and improving the efficiency of systems, such as photosensitive systems. In this context, the aim of this study was to obtain and characterize thin films using the self-assembly technique (layer by layer technique or LbL). The thin films were deposited on different substrates (glass coverslips, silicon and polystyrene). In this work two different multilayer sets combined with two different proportions of each solution system were deposited. The cationic system was composed by the poly(diallyldimethilammonium) (PDDA) organic polyelectrolyte solution and the cadmium selenide (CdSe) inorganic semiconductor colloidal solution. The anionic system was composed by the poly(acid acrylic) (PAA) solution and the titanium dioxide (TiO2) solution, respectively. The materials used for the achievement of films and nanostructured thin films produced were characterized through various techniques. The absorption regions of inorganic colloidal solutions were determined by UV-Vis spectroscopy and presented absorption at 320 nm (TiO2) and 440 nm (CdSe). The resulting inorganic nanoparticles diameter of TiO2 and CdSe were measured by X ray diffraction (XRD) and transmission electron microscopy (TEM), resulting in values at nanometric scale. It was observed in the nanoparticle TiO2 powder diffractogram that anatase is the most abundant phase, and that there was an overlap of the highest intensity diffraction peaks of TiO2 and CdSe, both at 2q = 25.3 °. The diffuse reflectance spectrum (RDUV-Vis) of self-assembled films presented values compatible with those of the film forming solutions. Using the wavelengths obtained from the UVVis and Vis-RDUV techniques it were possible to evaluate values for the energy band gap (Ebg) seminconductors TiO2 and CdSe. The thicknesses of the films were determined by profilometry and scanning electron microscopy (SEM) techniques, and they are in the micrometric order of magnitude. Using the SEM micrographs, it was possible to evaluate the surface of the films that show a high roughness, the formation of TiO2 clumps and the agglomeration spherical selenium clusters. In TEM images, the distribution of the semiconductor nanoparticles in cross-section of films can be observed, confirming agglomerations observed by SEM.