TiO2-SiO2 Thin Films Research Articles

Effects of heat treatment and TiO2 content on the optical properties of Eu3+ doped TiO2–SiO2 thin films

The photoluminescence properties of Eu3+-doped TiO2–SiO2 thin films were investigated. The films were deposited on silicon substrates by the sol–gel process using the dip-coating method. The molar ratio of TiO2 content was varied from 25% to 100%, while Europium concentration was fixed to 1%. The obtained films were calcinated at various temperatures ranging from 400°C to 1300°C, which allowed determining the optimal conditions for the Eu3+ luminescence. Meanwhile, the structure of TiO2–SiO2 powders, prepared in the same conditions as the films, was also studied by Raman spectroscopy. It revealed the role of Europium and SiO2 on the stabilization of the anatase phase and the importance of the silica matrix in the control of titania particle size.

Photoactive and self-cleaning TiO2–SiO2 thin films on 316L stainless steel

In this study, TiO2–SiO2 nanocomposite films with different amounts of SiO2 were prepared by sol–gel process and were coated onto stainless steel 316L. The effect of addition of various amount of SiO2 in the precursor solution on the photocatalysis, photo-generated hydrophilicity and self-cleaning property of TiO2 thin films was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, water contact angle measurements and UV spectroscopy. In the tested ranges of SiO2 content and sintering temperature, the highest photocatalytic activity and self-cleaning property were observed in the 15mol% SiO2 sample sintered at 750°C. Addition of less than 30mol% SiO2 had a suppressive effect on the transformation of anatase to rutile and on the crystal growth of anatase in the sintering heat treatment. Phase separation occurred in the composite films for SiO2 content of 30mol% or more.

Photocatalytic of TiO<sub>2</sub>-SiO<sub>2</sub> Thin Films Co-Doped with Fe<sup>3+</sup> and Thio-Urea in the Degradation of Formaldehyde by Indoor and Outdoor Visible Lights

In this work the photocatalytic activity of TiO2-SiO2 thin films co-doped with Fe3+ and thio-urea in the degradation of the gaseous formaldehyde was investigaged by indoor and outdoor visible lights. The films were synthesized by Peroxo Titanic Acid (PTA) method. The physicochemical properties of prepared samples were characterized using SEM and UV-vis absorption spectroscopy. It was found that the average film thickness of all coated samples was about 394 ± 5 nm. The band gap energy of un-doped and co-doped photocatalysts was 3.08 and 2.88 eV, respectively. The photocatalytic experimental results showed that the co-doped TiO2-SiO2 thin film yield higher photocatalytic efficiency. Under the outdoor light (sunlight in the shade condition) irradiation, with the initial concentrations of formaldehyde of 1000, 3000 and 5000 ppmV, the efficiencies of formaldehyde degradation were 94.7 %, 89.5% and 85.1 %, respectively. Under the indoor light (the fluorescent lamp) irradiation, with the same formaldehyde initial concentrations, the photocatalytic activities were 87.4%, 85.3% and 81.5%, respectively.

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO2–SiO2 thin film was prepared by self-assembly method by mixing SiO2 precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO2 and even anatase TiO2 but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO2 was incorporated into the film. The self-assembly TiO2–SiO2 thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO2 are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO2:TiO2) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.

Preparation and characterization of V2O5 doped SiO2-TiO2 thin films

Abstract In our investigation, V doped SiO2/TiO2 thin films were prepared on glass substrates by dip coating sol-gel technique. Chemical composition of the samples was studied by X-ray photoelectron spectroscopy (XPS). Transmittance of the samples was characterized using UV-VIS spectrophotometry. Subsequently band-gap energy (Eg) was estimated for these films. Powders obtained from sols were characterized by FTIR spectroscopy. It was found that vanadium decreases optical band gap of SSiO2/TiO2 films.

Effect of Co-Dopants in TiO2–SiO2 Thin films on the Formaldehyde Degradation

Titanium dioxide (TiO2)–silicon dioxide (SiO2) thin films were synthesized using the peroxo titanic acid approach (PTA) combined with the sol–gel method at low temperature around 100°C. The effects of type and amount of dopants of ferric (Fe3+) or thiourea (N-S) and co-dopants of Fe3+ and N-S on the films physicochemical properties and on the photocatalytic degradation of the methylene blue and formaldehyde under UV and visible light irradiation were investigated. Physicochemical properties of photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, wavelength-dispersive X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV–Vis spectroscopy. The results showed that the TiO2 crystal phases obtained from this method were exclusively anatase and the needle-like crystals have an average diameter of 10–25 nm. Compared with the single dopant of 1.0 wt.% Fe3+ or 0.125 wt.% N-S that was the optimal concentration for photocatalytic degradation of methylene blue and formaldehyde, the co-dopants of 0.125 wt.% N-S + 1.0 wt.% Fe3+ furthermore increased the degradation efficiency. Co-dopants of 0.125 wt.% N-S + 1.0 wt.% Fe3+ in TiO2–SiO2 films were considered to play synergistic roles in narrowing TiO2 band gap resulting in the higher methylene blue and formaldehyde degradation efficiency. Since the crystal grain size of TiO2–SiO2 films synthesized by the PTA method is small, in the visible light region, the high transmittance was attainable to 80% with no-doped and dropped to 50–60% with doped thin films.

Optical and hydrophilic properties of Cr doped TiO2–SiO2 nanostructure thin film

Cr doped TiO2–SiO2 nanostructure thin film on glass substrates was prepared by a sol–gel dip coating process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structural and chemical properties of the films. A UV–vis spectrophotometer was used to measure the transmittance spectra of the thin film. The hydrophilicity of the thin film during irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicated that Cr doping has a significant effect on the transmittance and super-hydrophilicity of TiO2–SiO2 thin film.

Photo-induced superhydrophilicity of nanocomposite TiO2-SiO2 thin film

In this work, TiO2 and TiO2-SiO2 thin films on glass substrates were prepared by the sol-gel dip coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. The super-hydrophilicity was assessed by water contact angle measurement. XRD measurements confirmed the presence of polycrystalline anatase and rutile phases in the films. The water contact angle measurements showed that addition of SiO2 has a significant effect on the super-hydrophilicity of TiO2 thin films, especially if they are stored in a dark place.

Room Temperature CVD of TiO<SUB>2</SUB> Thin Films and Their Electronic Properties

Amorphous TiO2 thin films and TiO2–SiO2 thin films were deposited for use in the gate oxide of Metal Oxide Semiconductor-Field Effect Transistor (MOS-FET). They were deposited by a novel CVD method using hydrolysis of Titanium IV isopropoxide and Tetra ethyl ortho silicate at room temperature and atmospheric pressure. Root mean square (RMS) of as-deposited TiO2 films was 0.28 nm. TiO2 films annealed at 400 � C in air showed anatase phase, but TiO2–SiO2 films didn’t crystallize below 700 � C. Dielectric constants of TiO2 films and TiO2–SiO2 films were about 40 and 20, respectively. Minima of equivalent oxide thickness of as-deposited TiO2 films and TiO2–SiO2 films were about 3.9 nm and 4.2 nm, respectively.

A Novel Label-Free Optical Biosensor Using Synthetic Oligonucleotides from E. coli O157:H7: Elementary Sensitivity Tests

SiO2-TiO2 thin films for use as fiber optic guiding layers of optical DNA biosensors were fabricated by the sol-gel dip coating technique. The chemical structure and the surface morphology of the films were characterized before immobilization. Single probe DNA strands were immobilized on the surface and the porosity of the films before the hybridization process was measured. Refractive index values of the films were measured using a Metricon 2010 prism coupler. On the surface of each film, 12 different spots were taken for measurement and calculation of the mean refractive index values with their standard deviations. The increased refractive index values after the immobilization of single DNA strands indicated that immobilization was successfully achieved. A further refractive index increase after the hybridization with target single DNA strands showed the possibility of detection of the E. coli O157:H7 EDL933 species using strands of 20-mers (5′-TAATATCGGTTGCGGAGGTG -3′) sequence.

Preparation of SiO<sub>2</sub>-TiO<sub>2</sub> Films of High Photo-Catalytic Activity in the Electric Field Heating-Treatment

In this paper the Li+, Sb3+-doped SiO2-TiO2 thin films, which were heat-treated with an applied electric field, were prepared by sol-gel dip coating. The crystallization of the thin films in the electric field heating-treatment was studied by X-ray diffraction (XRD) and atomic force microscope (AFM). The photo-catalytic activity of SiO2-TiO2 films was studied under the condition of an electric field heating-treatment and mixing with some additive such as Li+ and Sb3+. Finally, studies on photo-catalytic degradation showed that the Li+, Sb3+-doped SiO2-TiO2 films on the quartz glass, of high photo-catalytic activity, were successfully obtained in the electric field heating-treatment.

Monocomponent Powders and Thin Films in the Binary System SiO<sub>2</sub>–TiO<sub>2</sub>

In this work, we report the sol-gel alkoxide route preparation of nanostructured SiO2 and TiO2 powders as well as TiO2-SiO2 thin films obtained by dip-coating. Thermal analysis, morphology and structure were characterized for powders and correlation between preparation method and optical properties of binary materials (SiO2-TiO2) for thin films was approached. Spectroscopic Ellipsometry (SE), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) have been used for the physical characterization of the films.

Study on the Macro-Residual Stress of 304 Stainless Steel Coated with TiO<sub>2</sub>-SiO<sub>2</sub> Thin Films by Sol-Gel Process

X-ray diffraction (XRD) method to measure the residual stress in the metal substrate surface layer and the medial oxide layer between thin film and metal substrate was introduced and the sol-gel TiO2-SiO2 thin film was successfully prepared on SUS304 stainless steel substrate by dip-coating process. The macro residual stress existing in metal substrate was analyzed by XRD. It turns out that the compressive stress existing in the metal substrate surface layer decreases with the raising of heat-treated temperature and that the compressive stress of metal substrate surface layer and the tensile stress of the medial oxide layer increase with the increase of the withdrawal speeds of the sol-gel dip-coating. Based on the above study, colored stainless steels of high quality were prepared by sol-gel process for the first time.

Development of novel surfactant-templated nanostructured thin SiO2, and SiO2–TiO2 films

Nanostructured oxidic thin films are of interest due to their applicability in many different fields like filtration technology, catalysis, biomaterials and self purification. In this paper, we present sol–gel derived SiO2 and SiO2–TiO2 thin films with a new fingerprint-like nanostructure. The films were produced by dip-coating glass slides into the sol and a temperature treatment at 500 and 600°C. The characterization methods were FEGSEM and AFM. The dimensions of the nanostructured surface pattern were calculated from the AFM data with the power spectral density method.

TiO2 and TiO2–SiO2 thin films and powders by one-step soft-solution method: Synthesis and characterizations

Abstract Simple soft-solution method has been developed to synthesize films and powders of TiO2 and mixed TiO2–SiO2 at relatively low temperatures. This method is simple and inexpensive. Furthermore, reactor can be designed for large-scale applications as well as to produce large quantities of composite powders in a single step. For the preparation of TiO2, we used aqueous acidic medium containing TiOSO4 and H2O2, which results in a peroxo-titanium precursor while colloidal SiO2 has been added to the precursor for the formation of TiO2–SiO2. Post annealing at 500 °C is necessary to have anatase structure. Resulting films and powders were characterized by different techniques. TiO2 (anatase) phase with (1 0 1) preferred orientation has been obtained. Also in TiO2–SiO2 mixed films and powders, TiO2 (anatase) phase was found. Fourier transform infrared spectroscopy (FTIR) results for TiO2 and mixed TiO2–SiO2 films have been presented and discussed. The method developed in this paper allowed obtaining compact and homogeneous TiO2 films. These compact films are highly photoactive when TiO2 is used as photo anode in an photoelectrochemical cell. Nanoporous morphology is obtained when SiO2 colloids are added into the solution.

Compositional Tailored Sol-Gel SiO2–TiO2 Thin Films: Crystallization, Chemical Bonding Configuration, and Optical Properties

Thin films of SiO2–TiO2 composite oxides with various SiO2:TiO2 compositions were prepared by the sol-gel method, using tetraethylorthosilicate (TEOS) and titanium tetraisopropoxide (TTIP) as precursors. The composition, crystal structure, and chemical bonding configuration of the as-deposited and annealed SiO2–TiO2 thin films were analyzed using Rutherford backscattering spectrometry (RBS), glancing incident angle x-ray diffraction (GIAXRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Optical properties of the films were characterized by spectroscopic ellipsometry and ultraviolet-visible spectrophotometry. The Si/Ti ratios in the SiO2–TiO2 films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. When the TEOS/(TEOS + TTIP) ratio is greater than 40%, the SiO2–TiO2 thin films remain amorphous (without formation of TiO2 crystalline phase) after annealing at temperatures as high as 700 °C. FTIR spectra indicate that the quantity of Si–O–Ti bonding can be maximized when the TEOS:TTIP in the precursor is 80%:20%. The refractive index of the SiO2–TiO2 films increases approximately linearly to the mixing ratio of TTIP/(TEOS + TTIP). However, SiO2-rich films possess higher ultraviolet-visible transmittance than the TiO2-rich films. The modification of microstructure and chemical bonding configuration in the SiO2–TiO2 films by the composition and its influence on the optical properties are discussed.

XPS Studies on Composite TiO<sub>2</sub>-SiO<sub>2</sub> Thin Films Deposited on Metal Substrate by Sol-Gel

Through X-ray photoelectron spectroscopy, by the aid of Ar+ sputtering, chemical composition and the valence state of elements on surface and at depth of TiO2-SiO2 thin films and metal substrates have been studied. Results show that: on surface, elements of Cr, Mn, Ti, Fe exist in the form of their respective stable state, but Si is unstable and exhibits stoichiometrical disturbance when heat treated at 800°C; at depth, after sputtering for 5 minutes and 17 minutes, elements of Cr, Mn, Ti and Ni exist in the form of their respective stable state, but Si and Fe are unstable and exhibit stoichiometrical disturbances; at depth, after sputtering for 57 minutes, all of the Cr, Mn, Ti, Si, Ni and Fe exist in the form of their respective stable state. Results of chemical composition and their content by weight percent of TiO2-SiO2 thin films and metal substrates reveal that: Fe, Cr, and Mn diffuse from metal substrates to the thin films in scale; Ni diffuses few and Si collects to the metal substrate surface

Variable incidence infrared absorption spectroscopy of gel-derived silica and titania films

SiO2, TiO2 and mixed SiO2–TiO2 thin films were prepared, via sol-gel processing, by spin-coating on silicon wafer substrates. They were either dried at room temperature, or subjected to different heat treatments, from 600 °C up to 950 °C. Infrared spectroscopy was performed on these films, in transmission mode, using variable incidence, light, either natural or polarized. The longitudinal optical (LO) components of the rocking and asymmetric stretching Si–O–Si vibrations become more visible and the position can be more accurately determinated, respectively, with increasing incidence angles away from normal. These peak positions shift to higher frequencies with thermal treatment, as the films undergo a transition from the gel to the glassy state. In titania films, the detection of LO vibrations is less evident than in silica based-films, even at oblique incidence. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on the Superhydrophilicity of the SiO2-TiO2Thin Films Prepared by Sol-Gel Method at Room Temperature

Nanoscale SiO2-TiO2 composite thin films with the thickness of about 100 nm were prepared by sol-gel method at room temperature in air. The chemical states of the elements on the surface and near the surface were measured by XPS. The results showed that the Ti on/near the surface of the thin films existed not only as TiO2 but also as Ti2O3. Part of the TiO2 was changed to Ti2O3 after UV irradiation. The crystalline structure of the TiO2 in the SiO2-TiO2 thin films was anatase with the crystallite size of 14–20 nm. It was found that the thin film prepared at room temperature in air has good superhydrophilic property and has strong adherence to the substrate.

Photoluminescence of terbium-organic complex in aerosol–gel-derived planar waveguides

This work deals with the low-temperature preparation of optically active silica-based materials. Tb3+-doped silica monolithic gels were elaborated at 40 °C. Tb3+–SSA-doped SiO2–TiO2 thin films were deposited by an original sol–gel approach, the aerosol–gel process, and heat-treated at 150 °C. Organic complexation of terbium ions was used to improve the active properties of doped silica gels and thin-film samples. Spectroscopic characterisations are reported for these samples. Photoluminescence increase by a factor two was observed for complexation by sulphosalicylic acid.