Résumé:
The present work consists in the elaboration and the characterization of TiO2 thin
films by sol-gel method. Particular attention is paid to the influence of temperatures,
the annealing atmosphere, the thickness, the nature of the substrates and doping with
Fe element on the different structural, morphological, optical, dielectric and chemical
properties.
The different samples are characterized by the X-ray diffraction (XRD), atomic
force microscopy (AFM), Raman spectroscopy, FTIR spectroscopy, spectroscopic
ellipsometry, UV-Visible spectroscopy, m-lines spectroscopy and hydrophilic
measurements.
The structural study shows that the crystallization of the films occurs for critical
thicknesses. The thermal annealing under various atmospheres (air and oxygen) and
the presence of buffer layers between the TiO2 film and the substrate are important
factors affecting the formation and improving the structure of anatase and rutile
phases. The phase transformation anatase-rutile occurs at high temperature (800°C).
The SnO2 interfacial layer and the high doping level (7% at.) have the effect of
decreasing the temperature of this transformation.
The morphological study shows, in general, a uniform growth with relatively
low roughness, which bodes the optical quality of the films obtained.
The optical study shows that the values of the refractive indices derived using the
sem-infinite, Fourouhi-Bloomer and EMA models are in good agreement with those
of the literature. The study of the optical gap obtained by spectroscopic ellipsometry
and the UV-visible spectroscopy reveals some variation depending on various
parameters. The waveguiding measurements show that TiO2 films deposited directly
on the glass behave as single-mode waveguides in the two polarizations (TM and TE).
When SnO2 and ZnO films are used as buffer layers, we note the disappearance of
TM modes.
The dielectric study shows that the approach based on the Kramers-Kronig
analysis and Maxwell's equations is proved acceptable in comparison with other
known models.
The analysis of wetting water shows the super-hydrophilicity of TiO2/verre and
TiO2/(ZnO/glass) samples.
