Anatase TiO2 Thin Films Research Articles

Structural analysis of TiO2 and TiO2-Ag thin films and their antibacterial behaviors

TiO2 (rutile and anatase) thin films was first prepared using reactive sputtering, in an Ar+O2 plasma. In the 2nd stage of the experiment, various amounts (3, 7, and 10 at. %) of Ag was doped into the rutile film in order to form TiO2-Ag thin films. These films were annealed for one hour in Ar atmosphere, at 300, 400, and 500 °C. The films' structures were then examined using X-ray diffractometry. FESEM (field-emission scaning electron microscopy) was used to investigate the surface emergence of Ag particles. As for the examination of optical band gaps and absorption of these films, UV-Vis-NIR photometer was used. The results show that, in as-deposited condition, the addition of Ag might disrupt the growth of crystalline structure and cause the formation of amorphous films. After annealing, it is found that the structure tends to become anatase phase which is a metastable phase between amorphous titanium oxide and rutile. More importantly, the absorption of the Ag-doped films would be enhanced in the visible-light range. Some of the enhancement is clearly due to plasmon resonance effect. The Ag-doped samples have shown some antibacterial effect in dark. When irradiated with light, the samples show a synergistic behavior combining the bactericidal effect of Ag ions and photocatalytic effect of TiO2.

Low temperature preparation of transparent, antireflective TiO2 films deposited at different O2/Ar ratios by microwave electron cyclotron resonance magnetron sputtering

A serial of crystalline titanium oxide ceramic films were deposited at low temperature using microwave electron cyclotron resonance (MW-ECR) magnetron sputtering with different O2/Ar ratios. The influences of O2/Ar ratio on the deposition rate, morphology, crystalline nature, optical adsorption property of the obtained titanium oxide thin films were investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and UV–Vis spectra. Therefore, the optimum O2/Ar ratio for deposition of anatase TiO2 thin films on unheated glass substrate was realized in a MW-ECR magnetron sputtering process. The as-deposited anatase TiO2 films were transparent and were antireflective in the visible region.

Fabrication of highly efficient dye-sensitized solar cell and CO2 reduction photocatalyst using TiO2 nanoparticles prepared by spin coating-assisted sol–gel method

A sol–gel method was applied for fabrication of nanocrystalline anatase TiO2 thin films on ITO glass substrates and followed by rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). TiO2 nanoparticles were characterized by X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) and the absorption of dye on the TiO2 electrode was shown by UV–vis spectroscopy. By controlling different parameters including numbers of coated layers, the gap between two electrodes, sensitization time, and light source power, TiO2-based solar cells with high efficiency was achieved. The results show that a five time spin-coated TiO2 electrode with applying sealant and sensitization time of 24 h in N3 dye under illumination of 100 W cm−2 tungsten lamp give the optimum power conversion efficiency (η) of 6.61%. The increases in thickness of TiO2 films by increasing the numbers of coated layers can improve adsorption of the N3 dye through TiO2 layers to increase the open-circuit voltage (V oc). However, short-circuit photocurrents (J sc) of DSSCs with a one-coated layer of TiO2 films are smaller than those of DSSCs with five-coated layer of TiO2 films. It could be due to the fact that the increased thickness of TiO2 thin films also resulted in a decrease in the transmittance of TiO2 thin films. Also, this electrode was employed to photoreduce CO2 with H2O under tungsten lamp as light source.

Influence of sputtering power on structure and photocatalyst properties of DC magnetron sputtered TiO2 thin film

TiO2 thin films were deposited by DC reactive magnetron sputtering technique on silicon wafer and glass slide at sputtering power of 210W and 230W. A pure metallic titanium target was sputtered in a mixture of argon and oxygen gases. The distance of Ti-target to substrate holder (ds-t) was 120mm. The films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The photocatalytic activity was evaluated by the measurement of the decomposition of methylene blue after UV irradiation. It was found that the crystalline structure of TiO2 thin films strongly depended on the sputtering power. The mixed phase of anatas/rutile TiO2 thin films were successfully obtained with the sputtering power of 230W. While anatase TiO2 thin films were obtained with sputtering power of 210W. The TiO2 thin film with anatase structure exhibited the best photocatalytic activity.

Oxygen Partial Pressure Dependence of the Properties of TiO2 Thin Films Deposited by DC Reactive Magnetron Sputtering

Thin films of TiO2 have been deposited on glass and silicon wafers (100) substrates by DC reactive magnetron sputtering from a 99.995% pure titanium target. The influence of the oxygen partial pressure on the optical, crystallinity, surface morphology and UV-induced hydrophilic properties has been studied. The films were characterized by UV-VIS spectrophotometer, X-ray diffractometer, atomic force microscopy and scanning electron microscope. The UV-induced hydrophilicity of the films was measured by the contact angle variation. The results showed that the crystalline anatase, anatase/rutile or rutile films can be successfully deposited on unheated substrate. The best hydrophilicity was obtained on the well-crystallized anatase TiO2 thin film deposition with 5.0×10-3 mbar oxygen partial pressure. The optical band gap of TiO2 thin films increased with increasing oxygen partial pressure,from 3.21 to 3.28eV, with film thickness of 135nm.

Optical properties of anatase TiO2 films modified by N ion implantation

Anatase TiO2 thin films are deposited on K9 glass samples at different substrate temperatures by radio frequency magnetron sputtering. N ion implantation is performed in the as-deposited TiO2 thin films at ion fluences of 5 × 1016, 1 × 1017, and 5 × 1017 ions/cm2. X-ray diffraction, atomic force microscope, X-ray photoelectron spectroscopy (XPS), and UV–visible spectrophotometer are used to characterize the films. With increasing N ion fluences, the absorption edges of anatase TiO2 films shift to longer wavelengths and the absorbance increases in the visible light region. XPS results show that the red shift of TiO2 films is due to the formation of N–Ti–O compounds. As a result, photoactivity is enhanced with increasing N ion fluence.

Effect of Crystal Structure and Grain Size on Photo-Catalytic Activities of Remote-Plasma Atomic Layer Deposited Titanium Oxide Thin Film

The photo-catalytic activities of TiO2 thin films grown by remote plasma atomic layer deposition (RPALD) were investigated as a function of grain size and crystal structure. As the deposition temperature increased, it was shown that grain size of the anatase phase in the as-deposited TiO2 thin films progressively decreased. When the TiO2 films grown by RPALD were annealed at 900°C, the anatase TiO2 phase with relatively small grains provided large number of nucleation sites for formation of more stable rutile phase. On the other hand, the phase transition to rutile was retarded due to the reduction in grain boundaries in the case of the anatase TiO2 films with large grains. Thus, the anatase TiO2 phase with large grains has excellent thermal stability against the phase transition to rutile. Because the large grain boundary volume is a primary cause of degradation of photo-catalytic activity, the photo-catalytic activity of the TiO2 thin film was maximized when the anatase phase with large grains was formed in the TiO2 thin film. Therefore, RPALD can be effectively utilized to control the grain size of the as-deposited anatase TiO2 thin film with high thermal stability for potential application of photo-catalysts.

Preparation and Characterization of Lanthanum (La)-Doped TiO<sub>2</sub>

Lanthanum-doped anatase TiO2 coatings, which were composed of assemble crystalline of 50 nm diameter particles have been successfully fabricated by sol–gel dip-coating process on light leakage quartz fiber (LQF) which length is 15cm and diameter is 125μm. This was achieved by adjustment of the lanthanum-doped sol–gel parameters such as molar ratio of precursors in lanthanum-doped TiO2-sols, the ratio of titanium tetrabutoxide to polyvinyl alcohol, dip-coating velocity, drying duration in air, thermal treatment and number of cyclical time of the process. Titania nano crystals were prepared by ambient temperature in a liquid media using titanium tetrabutoxide as precursor, and the crystallization of amorphous precursor was preceded by peptizing with acid and then refluxing for a periodic time in homothermal water-bath. The photocatalytic properties of the lanthanum-doped TiO2 films were testified by the photo degradation of methyl orange. The lanthanum-doped anatase TiO2 thin films were characterized by XRD and TEM.

(001)-orientation of anatase TiO2 thin films on RbLaNb2O7 seed layer prepared by ELAMOD

By means of a metal-organic deposition process, the anatase TiO2 thin films with and without (010)-oriented RbLaNb2O7 seed layer prepared by an excimer laser assisted metal-organic deposition process were crystallized on silica glass substrates. The anatase TiO2 thin film on the substrate with the seed layer showed high (001)-orientation because of the small lattice mismatch between the (001)-TiO2 and (010)-RbLaNb2O7 planes, while the anatase TiO2 thin film without the seed layer was crystallized without any specific orientations. The Lotgering factor F(001) of the obtained (001)-oriented anatase TiO2 thin film was evaluated to be about 0.92. The (001)-orientation degree seems to be further improved by some surface modifications of the seed layer to stimulate the chemical bonding for the edge shared TiO6 octahedra along the c-axis.

Low-Temperature Synthesis and Gas Sensing Properties of Anatase TiO<sub>2</sub> Thin Films

Crystalline anatase TiO2thin films were obtained on glass substrates at 60°C, 75°C and 90°C, respectively, by liquid phase deposition (LPD) method without subsequent heat treatment. X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-Vis spectrophotometer were used to characterize the as-synthesized TiO2thin films. The H2sensing properties of the TiO2thin films based sensors were investigated. The results show that the gas sensors signal Ra/Rg (Ra: resistance in air, Rg: resistance in a sample gas) decreases with the increasing deposition temperature. The TiO2thin films obtained at deposition temperature of 60°C exhibited the maximum H2gas response at 350°C, and the magnitude of the sensor signal and the response time for 500ppm H2was 1.25 and 17s, respectively.

First-principles calculations of a corrugated anatase TiO2 surface

The structural, electronic and optical properties of a corrugated anatase TiO2 surface are studied using the pseudopotential density-functional theory (DFT). The calculation of the electronic and optical properties provides the electronic and optical band gaps. The optical band gap is calculated using the photon energy dependent imaginary part of the dielectric function that indicates the exact optical transitions from occupied valence bands to unoccupied conduction bands. The estimated optical band gap is higher than the electronic band gap at the Γ point and shows consistency with the experimental band gap of an anatase TiO2 thin-film. This result also shows the significant optical anisotropy in directions normal and parallel to the corrugated surface.

Photocatalytic degradation of TCE in dry and wet air conditions with TiO2 porous thin films

Porous TiO2-anatase thin films were prepared by the sol–gel route and used for the study of the influence of structural properties in their photocatalytic activity. Sols were prepared by using titanium isopropoxide with two types of modifier ligands, namely acetic acid and acetyl acetone, and pore generating agents such as polyethylene glycol, pluronic F-127 and polyethylene glycol hexadecyl ether (Brij 58). The photocatalytic activity for the degradation of trichloroethylene in air was evaluated under ultraviolet irradiation at different gas flows and water vapour contents. The photocatalytic activity depends on the nature of the pore generating agent which influences the TiO2 crystallite size and the textural properties of the final material. The samples obtained by using acetic acid as the modifier ligand and either Brij 58 or PEG as the pore generating agent exhibited the best photocatalytic behaviour even in the presence of high quantities of water vapour. The direct trichloroethylene oxidation pathway to CO2 is favoured at low water vapour contents, but an important generation of COCl2 is observed even at low water partial pressures.

Study of valence band structure of Fe doped anatase TiO2 thin films

We study the structural and electronic properties of Fe doped (4–8 at. %) and undoped TiO2 thin films deposited by pulsed laser deposition on Si(111) substrate. The films grow in single phase anatase structure of TiO2 as revealed by x-ray diffraction and Raman spectroscopy measurements. The Fe doped films reveal room temperature magnetic hysteresis behavior. We have probed the electronic environment of Fe in TiO2 matrix and its coupling to the cations, using photoelectron spectroscopy measurements. Photoelectron spectroscopic studies reveal the ionic state of Fe in TiO2, precluding the formation of Fe metal clusters. Valence band spectra of these films suggest that it primarily consists of O-2p derived state, however, Fe derived state is also observed in Fe doped films. Resonance photoelectron spectroscopy studies indicate that Fe ions are hybridized with Ti3+ defect states.

A Convenient Method for Synthesis of Nano-Titania Thin Films from Aqueous TiO<sub>2</sub> Precursor Sols

Anatase TiO2 thin films were prepared on glass substrates by dip-coating method with TiCl4 as the Ti precursor hydrolysis in a mixed solvent of alcohol and water. The effects of preparation parameters such as the alcohol species, the alcohol/water (A/W) ratio, and the dosage of TiCl4 (the volume ratio of TiCl4 and mixed solution) were investigated. The best preparation condition was optimized that with the isopropanol / H2O volume ratio of 65:35, the dosage of TiCl4 at 3%. XRD, SEM, TEM and UV–Vis photospectroscopy were used to analyze the characteristics of the solution and films. The films have a high hydrophilicity after illuminating with ultraviolet light, it have a good adherence and can be used as an efficient photocatalyst.

Scaling of flat band potential and dielectric constant as a function of Ta concentration in Ta-TiO2 epitaxial films

Electrochemical impedance spectroscopy measurements of pulsed laser deposited single crystal anatase TiO2 thin films with various concentrations of Ta substituting for Ti were carried out. The qualities of the films were characterized by X-ray diffraction and Rutherford back scattering-channeling measurements. UV-visible measurements show a systematic increase of the bandgap with Ta incorporation. Corresponding Mott-Schottky plot was applied to obtain a continuous shift of the flat band potential with increasing free charge carrier (provided by Ta) concentration. This was verified theoretically by ab initio calculation which shows that extra Ta d-electrons occupy Ti t2g orbital with increasing Ta concentration, thereby pushing up the Fermi level. The Mott-Schottky results were consistent when compared with Hall effect and temperature dependent resistivity measurements. From the measured deviation of carrier densities from Hall and Mott-Schottky measurements we have estimated the static dielectric constant of the TiO2 as a function of Ta incorporation, not possible from capacitive measurements.

Spectroscopic studies of anatase TiO2 thin films prepared by DC reactive magnetron sputtering

Anatase titanium dioxide (TiO2) thin films were deposited on unheated calcium fluoride substrates by DC reactive magnetron sputtering at different oxygen partial pressures and were characterized by X-ray diffraction (XRD), Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and Vacuum Ultraviolet Spectroscopy (VUV). Photoabsorption spectra of anatase TiO2 thin films are reported in the energy range 3.9–10.8eV (320–115nm). Electronic state assignments have been suggested for each of the observed absorption bands. These thin films show the presence of water which has been confirmed by VUV and Fourier Transform Infrared Spectroscopies.

Di- and Tri-iodide Reactivity at Illuminated Titanium Dioxide Interfaces

A photoelectrochemical cell designed to characterize interfacial electron transfer at potentiostatically controlled mesoporous nanocrystalline (anatase) TiO2 thin film electrodes was employed to characterize the reactivity of TiO2 with di- and tri-iodide in acetonitrile solution. Tri- and di-iodide, I3− and I2•−, were generated by direct excitation of iodide (266 nm), band gap excitation of TiO2 (355 nm), or both. The first iodide oxidation product observed spectroscopically after pulsed laser excitation was di-iodide, I2•−. The yield of I2•− measured 0.1 μs after pulsed 355 nm laser excitation decreased with the application of a forward bias. Under all conditions studied, there was no direct evidence for a reaction between TiO2 and I2•−, even when the concentration of trapped electrons, TiO2(e−)s, was increased with a forward bias. Di-iodide was found instead to disproportionate to yield tri-iodide, I3−, and iodide with a disproportionation rate constant that was within experimental error the same as that measured in fluid acetonitrile solution, k = 3 × 109 M−1 s−1. Spectroscopic evidence for a reaction between TiO2(e−) and I3− was observed. The kinetics for this reaction were complex and highly dependent on the TiO2(e−) concentration, behavior qualitatively consistent with a multiple trapping model. These findings may have relevance to unwanted charge recombination processes in dye-sensitized solar cells.

Structural and magnetic properties of Mn-doped anatase TiO2 films synthesized by atomic layer deposition

Mn-doped anatase TiO2 (Mn: 1.2, 2.4 at%) thin films were grown on Si(100) via atomic layer deposition (ALD). The synthesis utilized Ti(OCH(CH3)2)4 and H2O as ALD precursors and Mn(DPM)3 as a dopant source. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO2 matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, and density were investigated with scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. All ALD-synthesized films exhibited room-temperature ferromagnetism; the microstructure, density, and magnetic field-dependent magnetization of the TiO2 varied with the concentration of Mn. ALD permits precise composition and thickness control, and much higher process throughput compared to alternative techniques.

Blue/near UV light emission from hybrid InN/TiO2 nanoparticle films

We report on the enhancement of photoluminescence (PL) from anatase TiO2 thin films covered by InN nanoparticles prepared using plasma enhanced chemical vapor deposition (PECVD). The SEM images and X-ray diffraction spectra illustrate the strong interaction between the InN particles and the TiO2 films. UV-Vis absorption spectra indicate that the InN particles have an increased absorption in the visible light region and may sensitize the TiO2 films. The strong PL band observed in the anatase TiO2 thin films with the addition of InN may have been due to an increased localization of impurities and/or defect-trapped excitons.

Epitaxy of Porous and Photocatalytically Active TiO2 Films at 50°C

Epitaxial anatase TiO2 thin films were grown on (001) oriented SrTiO3 single crystal substrates by liquid phase deposition at 50°C. The film consisted of nanosized crystallites and exhibited a significant void fraction of 31 %. This contributed to the cracking of thicker films due to the generation of capillary stresses in the nanosized pores during drying. This porosity also comes in useful during the photodegradation of a methylene blue dye by an as-grown film.