Résumé:
This work is focused on preparation and characterization of thin layers of titanium oxide (TiO2) undoped and doped with heavy elements such as mercury, lead and zinc prepared by sol-gel method and deposited on various substrates (glass, silicon and ITO). In this study we used various investigative techniques: XRD, Raman spectroscopy, FTIR, UVVisible-NIR, Photoluminescence, Profilo-meter, SEM, AFM and spectroscopy Electrochemical potential.
DSC and XRD results show that the doping TiO2 xerogels with Hg and Pb accelerated crystallization compare of these doping with Zn which causes a delay of the crystallization of titanium oxide. The doped thin films obtained crystallize at low temperature on the titanium oxide structures, but with the increasing annealing temperature we distinguish the appearance of new phases corresponding to the doping elements this according to the type dopant. Raman and FTIR spectra confirm the results obtained by XRD and Raman spectroscopy by the appearance of vibrational bands corresponding to the same phases.
The micrographs of doped thin films show a morphology consisting of various nanostructures varied depending on the nature of the dopant and the annealing temperature.
Thin films of TiO2 doped Hg crystallizes in the form of nanoparticles, nano-sheets and nanotubes, the doping by Pb crystallizes with nano-structure of nonporous, nanotubes while doping with zinc shows the crystallization of the films with porous, nanowires and nanorodes structure .The grain size increases as the annealing temperature increases. The AFM images
correlates the observations of SEM are composed of many nanostructures with high density.
Characterizations by UV-Visible-NIR spectrophotometry, ellipsométerie and the PL spectroscopy show that the nature of dopant and the annealing temperature and the thickness of films can improve the optical properties of TiO2. Firstly, the elevation of these parameters increases the transmittance, the refractive index and decreases the optical gap; on the other hand, the doping effect causes a shift to larger lengths. This discrepancy confirmed the results obtained by photoluminescence (PL).
Characterizations I = f (v) of the thin films shows that the doping improve the properties of thin films they can be used in different application such as gas sensing and the photovoltaic field.
