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Growth, optical, and wettability properties of iron modified titania and ferropseudobrookite thin films

TitleGrowth, optical, and wettability properties of iron modified titania and ferropseudobrookite thin films
Publication TypeArticolo su Rivista peer-reviewed
Year of Publication2021
AuthorsFerrara, Maria Cristina, Mazzarelli S., Schioppa M., Pilloni L., and Tapfer Leander
JournalJournal of Applied Physics
KeywordsChlorine compounds, Contact angle, Domain size, Energy gap, Fe 3+, Fe-doped, glass, Light absorption, Lime, Modified titania, Molar ratio, Morphology, Open circuit voltage, Optical correlation, Optical-, Oxygen vacancies, Property, Si substrates, Silicon wafers, Sol-gel process, Substrates, Surface morphology, Thin films, Thin-films, TiO 2 thin film, Titanium dioxide, Water absorption, Wetting

Iron (Fe)-modified titanium dioxide, Fe-TiO2, thin films with molar ratios Fe:Ti = 1:360, 1:60, and 1:30 and Fe-pseudobrookite, FeTi2O5 (molar ratio Fe:Ti = 1:2), were grown by the sol-gel process using acid-catalyzed solutions prepared with titanium isopropoxide and iron(III) chloride hexahydrate as Ti and Fe precursors, respectively. The layers were deposited by dip-coating onto soda-lime glasses and (100)-Si substrate wafers, and their chemical composition, crystal structure, and surface morphology were investigated in detail. For the low Fe-doped samples, the experimental results clearly indicate the formation of Fe-O-Ti heterolinkages. The films have an amorphous structure and high flatness surfaces if grown onto glass substrates. On the contrary, if grown onto (100)-Si substrates, they exhibit a granular structure (domain size ∼12 nm) made of a solid solution of Fe3+ ions within the anatase TiO2 lattice. For coatings with the molar ratio Fe:Ti = 1:2 (high Fe content), morphological investigations show the formation of wrinkled surfaces characterized by dendritic structures. X-ray diffraction measurements confirm the formation of nanocrystallites (domain size ∼15 nm) of pure, single-phase orthorhombic FeTi2O5. Wettability measurements conducted on amorphous low Fe-doped TiO2 samples revealed superhydrophilic properties with a surface-water contact angle <1°, whereas optical absorption and reflectance measurements yield bandgap widening and narrowing. A bandgap narrowing occurs with the formation of oxygen vacancies and of Ti3+ levels, but if the concentration of oxygen vacancies and Ti3+ levels increases, more electron donors are generated, which shift the Fermi level to the conduction band. This widening of the bandgap (blue shift) can be explained by the Burstein-Moss effect. The correlation of the large optical bandgap (3.61 < Eg < 3.74 eV) and the wettability results are interpreted and discussed with the presence of oxygen vacancies and Ti3+ and Fe3+ sites in the TiO2 matrix. © 2021 Author(s).


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Citation KeyFerrara2021