Abstract:
"This work is devoted to the elaboration and characterization of [SiO2/(TiO2 undoped)]
and [SiO2/(TiO2 doped Ni)] systems, obtained by the sol-gel process. In this study, we have
shown the influence of the drawing speed, the annealing temperature, holding time, the
number of bilayers and the doping level on the optical and structural properties of these
systems. For this reason, various investigative techniques were used: XRD, Raman
spectroscopy, FTIR, SEM, SIMS, UV-Vis-IR, photoluminescence and m-lines.
The results obtained by X-ray and Raman show that the systems crystallize only in
anatase phase whatever is the operating conditions. We observe a decrease of the
[SiO2/(undoped TiO2)]S1 system grain size according to the elevation of both steeping speed
and number of bilayers. By cons, grain sizes of [SiO2/(undoped TiO2)]S2 and
[SiO2/(Ni:TiO2)]S2 systems increase upon of annealing temperature and hold time increase,
however they decrease when number of bilayers and Ni content increase.
The UV-Vis-IR spectra of [SiO2/(undoped TiO2)]S2 system illustrate that the stop band
width and the coefficient transmission decrease with bilayers number, annealing temperature,
and duration. While, those corresponding to [SiO2/(Ni:TiO2)]S2 system show, on the one hand,
that the stop band width decreases with increasing Nickel content whereas it increases as a
function of increasing the annealing temperature and duration. On the other hand, the
elevation of these parameters causes the decrease of transmission coefficient as a function of
Ni content increase. Thus, the effect of Nickel causes, on the one hand, a red-shift which is
accorded to the anatase grains size growth and on the other hand, it leads to a blue-shift,
which is attributed to their decrease. These shifts are confirmed by the results of
photoluminescence (PL).
M-lines spectroscopy of [SiO2/(Ni:TiO2)]S2 system shows that the insertion of Nickel
within TiO2 matrix increases the system thickness, decreases both its refractive index and
loss. Also, it shows that the system has two guided modes: TE0 and TE1."
