Sol-gel Derived TiO2 Thin Films Research Articles

Thickness dependence of structural, optical and morphological properties of sol-gel derived TiO2 thin film

In this research, Titanium dioxide (TiO2) thin films with different thicknesses were deposited on glass substrate by the sol - gel technique. Formation of TiO2 thin films was confirmed by EDAX spectra. The effect of thin film thickness on the structural, optical and morphological properties of the thin films was respectively analyzed by x-ray diffraction (XRD), UV–vis spectroscopy and atomic force microscopy (AFM). XRD measurements reveal the amorphous structure of the thin films before thermal treatment, while the thin films have crystalline phases after annealing at 600 °C. The XRD patterns also showed the dominant anatase phase in thin films structure. Moreover, peaks that belong to the Brookite phase appear as the thin film thickness increases. Brookite is the rare phase which is hardly gained and is suitable for photo catalytic applications. Crystalline transformation from anatse to anatas- brookite is attributed to grain size increase as increase of thin film thickness. Increase of grain size as a result of thin film thickness increase affect on the structural, optical and morphological properties. In addition, the weight fraction of brookite, grain size, lattice parameter and dislocation density were computed. The direct allowed band gap of TiO2 thin films with thickness of 50 nm to 150 nm was found to reduce in the range of 3.788 eV to 3.687 eV. The extinction coefficient, refractive index, susceptibility and porosity of the thin films were measured at the wavelength of 550 nm. Root mean square (RMS) roughness of the thin films increases as the thin film thickness increases.

Effective Richardson Constant of Sol-Gel Derived TiO2Films in n-TiO2/p-Si Heterojunctions

The effective Richardson constant of sol–gel derived TiO2 thin film has been estimated possibly for the first time from temperature-dependent current–voltage ( ${I}$ – ${V}$ – ${T}$ ) characteristics of p-Si/n-TiO2 thin-film heterojunction diode by including the barrier height inhomogeneity at p-Si/n-TiO2 interface. The thermionic emission theory-based ${I}$ – ${V}$ – ${T}$ characteristics have been modified by assuming a Gaussian distributed barrier height at the heterojunction interface. The Richardson plot shows a nearly ideal Richardson constant of ~1265.57 Acm−2K−2, which is not only very close to its theoretical value of ~1200 Acm−2K−2 for n-TiO2 (with ${m} ^{\ast }_{n}= 10 {m} _{0}$ ), but also the first result reported.

Composition, microstructure and SERS properties of titanium nitride thin film prepared via nitridation of sol–gel derived titania thin films

The titanium nitride thin film was successfully prepared via direct nitridation of the sol–gel derived TiO2 thin film at different temperatures in ammonia gas. The composition, microstructure and optical properties of the thin films were characterized in order to investigate their effect on the surface‐enhanced Raman scattering (SERS) performance of the thin films. With the nitridation temperatures increasing, the anatase phase transformed into titanium nitride phase in the films and the concentration of nitrogen incorporation increased accordingly. Consequentially, the sol–gel derived TiO2 thin film was converted to non‐stoichiometry titanium nitride (TiOxNy) thin film, as determined by X‐ray diffraction (XRD), RAMAN and X‐ray photoelectron spectroscopy (XPS). As a result, a blue‐shift of the surface plasmon resonance absorption peaks and narrowing optical band gap of the thin films were observed, leading to the improvement of SERS performance via electromagnetic enhancement mechanism and charge‐transfer effect. In addition, the surface of thin films became gradually rough with the nitridation temperatures increasing, ascribed to the growth of titanium nitride crystal grains. Most of all, the thin films nitrided at 1000 °C had the most rough surface, and many ‘hot spots’ formed on the thin film surface accordingly, which were favorable for enhancing SERS‐active, and thereby the thin films exhibited the largest SERS enhancement. Copyright © 2017 John Wiley & Sons, Ltd.

Constructing BiVO4/Graphene/TiO2 nanocomposite photoanode for photoelectrochemical conversion applications

BiVO4/Graphene/TiO2 as a novel nanocomposite photoanode was designed, synthesized and characterized for photoelectrochemical application. BiVO4/Graphene nanocomposite was initially synthesized by photocatalytic process and then, BiVO4/Graphene/TiO2 nanocomposite thin film was prepared by deposition of the BiVO4/Graphene solution onto the surface of sol–gel derived TiO2 thin film. Morphology, crystal structure, surface chemical composition and optical properties of the synthesized BiVO4/Graphene/TiO2 nanocomposite thin film were characterized and compared with the BiVO4/Graphene and pure TiO2 samples. Observations of scanning electron microscopy (SEM) images revealed that the surface of the TiO2 thin film was modified by the BiVO4/Graphene with high surface area. According to X-ray diffraction (XRD) analysis, formation of anatase and monoclinic phase was confirmed for crystalline structure of TiO2 and BiVO4, respectively. UV–visible absorption spectra of the samples showed that the absorption edge and intensity of the BiVO4/Graphene/TiO2 nanocomposite film were increased with respect to the TiO2 film. The BiVO4/Graphene/TiO2 nanocomposite photoanode yielded a photocurrent density of ∼1.30A/m2 as compared to 0.27A/m2 for the TiO2 at 0.8V vs Ag/AgCl under UV–visible irradiation in similar condition. The improved photoelectrochemical activity is believed due to the enhanced light absorption and higher surface area of BiVO4/Graphene as well as better charge transfer of the photogenerated carriers at the BiVO4/Graphene/TiO2 interfaces via Graphene.

Tribological performance of fluoroalkylsilane modification of sol–gel TiO2 coating

This paper explores the possibility of making coatings with super friction-reducing and wear protection properties by using both sol–gel and self-assembling techniques. The thin film of TiO2 was firstly prepared on glass substrates via a sol–gel method, followed by sintering at 480°C. The self-assembled monolayer of Fluoroalkylsilane (FAS) were then prepared on TiO2 thin film to obtain TiO2–FAS dual-layer film. The contact angle measurement and X-ray photoelectron spectroscopy were used to determine the wetting behavior and chemical structure of films, respectively. The friction behavior of films sliding against a steel ball was examined on a macro friction and wear tester. It is shown that FAS is strongly adsorbed on sol–gel derived TiO2 thin film, making it strongly hydrophobic. Good friction-reducing and wear protection behavior is observed for the glass substrate after duplex surface-modification with sol–gel TiO2 and top layer of FAS.

Synthesis and characterization of sol-gel derived TiO2 thin films: Effect of different pretreatment process

Titanium dioxide (TiO2) thin films have been successfully synthesized deposited on glass substrates by the sol-gel dip-coating method through different pretreating processes, including heated at 100, 500°C, via freeze drying, microwave heating for 10 min and subsequently annealed at 500°C for 2 h. The as-synthesized TiO2 films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and ultravioletvisible (UV-vis) absorption spectra analysis technology. The preparation of the precursor sols and TiO2 films were described in detail. Effects of 100, 500°C, freeze drying and microwave heating pretreatment on crystalline structure, surface morphology, roughness, particle size, optical property and electronic transition of TiO2 thin films have been primarily investigated. The XRD results demonstrate that the TiO2 films were well-crystallized and consisted of anatase TiO2 phase only with (101) plane. The average crystalline size is only about 15 nm at 100°C pretreatment and the absorption edge shifts to shorter wavelength comparing with that at 500°C, freeze drying and microwave heating pretreatment. Pretreatment process is important during the preparation of thin films and has obviously effect on the structure and optical property of TiO2 films due to the different heating mechanisms.

Effect of annealing temperature on the photocatalytic activity of sol-gel derived TiO2 thin films

Transparent TiO2 thin films were deposited on glass substrates by a sol-gel dip coating technique, where crystallinity can be achieved at a relatively low annealing temperature. In this sol-gel preparation technique, acetic acid was used as a catalyst. Repetitive dip coating and drying, with a single annealing has made this technique easier to prepare TiO2 thin film with desired thickness within a short period of time. The crystallographic and optical properties of TiO2 films were investigated in detail. The photocatalytic activity was evaluated by the measurement of decomposition of methanol under UV-visible irradiation. The rate of decomposition of gaseous methyl alcohol depends on the structures and surface properties of the TiO2 films. The structure of the TiO2 films, prepared at various annealing temperatures, shows different crystallinities. Although crystallinity has been observed for 300°C annealing temperature, it improved with increasing annealing temperature. The average transmittances of the TiO2 films slightly decrease with the increase of the annealing temperature in the range of 900–380nm. The optical transmission edge of the TiO2 films, annealed at different annealing temperatures shifts toward higher wavelength with higher annealing temperature. All the as-deposited TiO2 films successfully photocatalyzed methanol to CO2 and H2O, measured by Fourier transform infrared spectrometer. The decomposition efficiency of TiO2 films increased with decrease of annealing temperature. The surface morphology of all the samples was investigated by field emission scanning electron microscopy and atomic force microscopy measurements. The higher photocatalytic activity of the sample prepared at lower annealing temperature was explained by the effect of more porous structure with smaller grains and open surface morphology of the sample.

Influence of physico-structural properties on the photocatalytic activity of sol-gel derived TiO2 thin films

Sol-gel TiO2 films were deposited from various sols and heat-treated at different temperatures. Fourier transform infrared spectroscopy, ellipsometry, X-ray diffraction, and scanning electron microscopy methods have been used to study physico-structural properties of the films. These properties are discussed with respect to the experimental parameters. It is shown that, depending on sol formulations and annealing temperatures, a large range of crystallite size, crystallization degree, film porosity, and surface morphology can be covered. The photocatalytic properties of the films have been studied in relation to their physico-structural properties through the photodecomposition of malic acid. This study shows that the photocatalytic activity undergoes a complex dependence on the physico-structural properties.

Properties and Photoelectrocatalytic Behaviour of Sol-Gel Derived TiO2 Thin Films

Titanium dioxide (TiO2) thin films have been prepared on indium doped tin oxide (ITO) glass by sol-gel dip-coating method. Properties of the films were determined as a function of heat-treatment by X-ray diffraction, scanning electron microscopy and photoelectrochemical tests. The films heat-treated at higher temperatures show better crystallinity and photoresponse. The microscopic structure on the film after heat-treatment is attributed to the incorporation of organic polymer into the precursor solution. The performance of the electrodes treated at different temperature on photoelectrocatalytic degradation of methyl orange was investigated. The effect of applied potential and the ability of the electrode to be repeatedly used in photoelectrocatalytic degradation were also evaluated.

Influence of Anatase–Rutile Phase Transformation on Dielectric Properties of Sol–Gel Derived TiO2 Thin Films

Effects of annealing temperature on the structural and dielectric properties of sol–gel derived TiO2 thin films were systematically investigated. Thin films annealed at various temperatures showed pure or mixed phases of anatase and rutile. As-deposited films started crystallization below 600°C and fully crystallized into the anatase phase at 800°C, followed by transformation to the rutile phase above 850°C. Dielectric properties of thin films with various phases were studied by LCR-meter using the metal–insulator–metal (MIM) structure. Dielectric constants of thin films increased from 40 to 147 as the portion of rutile phase increased from 0 to 95%, while dielectric losses decreased from 0.011 to 0.001. Temperature dependence of dielectric constants of thin films was also investigated. The dielectric properties of TiO2 thin films were discussed in terms of phase constitution, crystallinity, and preferred orientation.

Photocatalytic Characteristics of TiO2 Thin Films Prepared by Dc Reactive Magnetron Sputtering with added H2O

A high-performance photocatalytic TiO2 thin film was successfully obtained by dc reactive magnetron sputtering with added H2O. The film was deposited onto SiO2-coated glass at a substrate temperature of 300°C using a titanium metal target in a combined Ar, O2 and H2O atmosphere. Photocatalytic performance was evaluated by measuring the change in concentration of methylene blue (MB) under UV irradiation. The photocatalytic performance of the film increased as the quantity of added H2O increased: when 70 sccm of H2O was added, the decomposition capability was about 1.6 times greater than a reference sample (sol–gel-derived TiO2 thin film). The film was characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), UV-VIS-NIR spectrophotometry, attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR), and photoluminescence spectrometry. Included in the film were a large number of OH groups. The surface morphology of the film had a domain structure, with each domain consisting of many sputter grains with the same orientation. The number of oxygen vacancies level in the forbidden band decreased as the quantity of H2O added during deposition increased. In addition, the Ti–OH dependent peak intensity increased when H2O was added. It was observed that this process would enable us to hydrogenate TiO2 more easily and thereby improve photocatalytic performance.

Enhancing photocatalytic activity of the sol-gel derived TiO2 thin films by nitric acid treatment

Enhancing photocatalytic activity of the sol-gel derived TiO2 thin films by nitric acid treatment