The preparation of a TiO2 thin film was investigated
by a newly developed two-dimensional
(2D) sol−gel process. When a chloroform solution of monomer or
tetramer of tetrabutoxytitanium (TBT) was spread on the surface of an aqueous subphase, the TBT
was hydrolyzed
and polycondensed at the air/water interface to give floating gels.
These gels were gathered
by 2D compression to yield a uniform gel film on the water surface.
The addition of chelating
agents such as acetic acid and acetylacetone to the aqueous subphase or
spreading solution
was effective in suppressing the 2D hydrolysis/polycondensation
reactions and in increasing
the stability of the floating gel film. Up to 20 layers of the
floating gel film prepared on
aqueous acetic acid could be quantitatively transferred onto a suitable
substrate using
Langmuir−Blodgett techniques. The addition of
n-octadecyl acetoacetate in the spreading
solution of monomeric Ti butoxide and ethoxide resulted in quantitative
transference of the
gel films onto substrates without a limitation on the number of
depositions. The deposited
TiO2-based gel films could be converted into nanothick
TiO2 films by calcination at 773 K
for 30 min. It was suggested that the oxide films prepared from
gel films of less than a few
tens of layers were composed of quantum-size TiO2
particulates. The thickness and the
density of the nanoparticulate TiO2 films could be
controlled by the number of deposited gel
film layers and the surface pressure of the gel film layer during
deposition. The controllable
thickness of the TiO2 film by one deposited gel film layer
was estimated to be 2−3 Å.
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