Optical Properties Of TiO2 Films Research Articles

Structural and Optical Properties of TiO<sub>2</sub> Thin Films Prepared by Thermal Oxidation of Ti Thin Films

Titanium dioxide (TiO2) films were prepared by thermal oxidation from Ti films. The Ti films were deposited on glass and silicon (100) wafer substrate by dc magnetron sputtering and subsequent with thermal oxidation process. The crystal structure and morphology of TiO2 films were estimated by using X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The optical property of TiO2 films was determined by UV-Visible spectrophotometer. The influences of annealing temperature between 200 to 500°C in air for 1 hour on the structure and optical properties of TiO2 films were investigated. The increasing of annealing temperature was directly affected the phase transition from Ti to TiO2. The optical and structural properties of TiO2 films are the best exhibited with increasing the annealing temperature at 500 °C.

The effect of ion source working power on the composition and optical properties of TiO2 films bombarded by N ion beam

At room temperature, the titanium dioxide (TiO2) films were deposited by the direct current pulse magnetron sputtering. Then the TiO2 films were in-situ bombarded by the N ion beam, which doped the N ions into the TiO2 films. By this way, the N doped TiO2 (N–TiO2) films were prepared. Varying the working power of the ion source, the N–TiO2 films with different composition and properties were obtained. Characterization by X-ray photoelectron spectrometry showed that the N ions mainly reacted with Ti to formed OTiN bonds and the doping depth exceeded 100nm. With the working power of ion source in 150W, the atom percent of N, mean absorbency in visible range, and band gap could reach at the optimal value, which was 22.9at.%, 44.6%, and 2.81eV, respectively. With increasing the working power of ion source, the atom percent of N and the mean absorbency in visible range, as well as the band gap, decreased and increased, respectively. With these results, one conclusion could be deduced that the composition and optical properties of N–TiO2 films could be influenced by the N atom percent and chemical bond structure of Ti, which in turn was controlled by the working power of N ion source.

Influence of Ni doping on phase transformation and optical properties of TiO2 films deposited on quartz substrates by sol–gel process

The Ni-doped TiO2 films were synthesized on quartz substrates by the sol–gel method. Results from X-ray diffraction and Raman spectra indicate that Ni doping catalyzes the anatase-to-rutile transformation. When Ni content is up to 10mol%, the transformation has been finished. The dielectric functions of Ni-doped TiO2 films were extracted by fitting transmittance spectra according to the Adachi's dielectric function model. The optical band gap decreases from 3.64eV to 3.51eV with increasing Ni content. The results suggest that the acceleration of phase change and variation of optical properties may be related to defects due to Ni doping.

Preparation and Characterizations of Yb-doped TiO2 Photocatalyst Films prepared by RF-Magnetron Sputtering Process

Yb-doped titanium dioxide (TiO2) films deposited on glass substrate were prepared by radio-frequency (RF) magnetron sputtering. The effects of total sputtering pressure and Yb doping on the phase structure, surface morphology, surface roughness and optical properties of TiO2 films were investigated. The results showed that all of Yb-doped TiO2 films deposited under pure Ar and Ar/O2 gas mixture at substrate heating temperature 500°C consisted of well crystalline anatase. It was demonstrated that the surface morphology and roughness of deposited films were strongly affected by the total sputtering pressure. The film sputtered under higher pressure (3Pa) has higher surface roughness with porous structure. Moreover, the increasing in surface roughness of deposited films when doping with Yb was observed. The absorption edge of transmittance of Yb-doped TiO2 film was red-shifted compared to the pure TiO2 film.

The Effect of Substrate Temperature on the Spray-Deposited TiO<SUB>2</SUB> Nanostructured Films for Dye-Sensitized Solar Cells

The nanostructured TiO2 films have deposited on SnO2:F (FTO) coated glass substrate by spray pyrolysis technique at different substrate temperatures of 200-500 degrees C. The structural, surface morphological and optical properties of TiO2 films significantly vary with the substrate temperature. The surface of the TiO2 films deposited at 400 degrees C shows the nanoflakes and short nanorods (approximately 130 nm) like structures while the TiO2 films prepared at 500 degrees C shows only the nanoflakes like structures. The band gap of the TiO2 films prepared at higher temperatures (300-500 degrees C) becomes narrow due to presence the rutile phases in their crystal structure. Ruthenium (II) complex as a dye, KI/I2 as an electrolyte and carbon on FTO glass as a counter electrode has used to fabricate the dye-sensitized solar cell (DSC). The TiO2 film deposited at 400 degrees C has showed the best photovoltaic performance in DSC with the efficiency of 3.81%, the photovoltage of 773 mV, the photocurrent of 8.34 mA/cm2, and the fill factor of 56.17%. The photovoltage of the DSC increases with the increase of substrate temperature during the deposition of TiO2 films. Moreover, all the DSCs exhibit reasonably high fill factor value.

Effect of Ozone on Deposition of Titanium Oxide Films from Tetraisopropoxide

The effect of ozone on chemical vapor deposition of titanium dioxide films from titanium tetraisopropoxide (TTIP) has been experimentally studied. The influence of process parameters on the growth rate, structural and optical properties of TiO2 films deposited in the TTIP-Ar, TTIP-O2-Ar and TTIP-O2-O3-Ar reaction systems have been compared taking into account the results of FTIR measurements of the reaction gas phase. Ozone allows to decrease minimal deposition temperature providing formation of high quality titanium dioxide films to 240 {degree sign}C.

Effect of annealing on the structural, electrical and optical properties of nanostructured TiO2 thin films

AbstractNanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO2 films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV‐Visible spectroscopy and electrical studies. X‐ray diffraction studies showed that the as‐deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator‐Wemple and Didomenico model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Study of photocatalytic activity of TiO2 thin films prepared in various Ar∕O2 ratio and sputtering gas pressure

In this study, various transparent TiO2 films were deposited on unheated glass-slide substrates by dc reactive sputtering technique. For one set of samples the ratio of Ar to O2 (GR) was varied from 9:1 to 6:4 for a fixed sputtering pressure of 0.8Pa, while for another set of samples the total working pressure was varied from 0.2to0.8Pa for a fixed GR of 7:3. 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 structure of the TiO2 films, prepared with various GR, varied from amorphous to different crystalline phases. Similarly sputtering pressure variation induced change of crystalline phase and crystallinity of TiO2 films. The crystallinity improved greatly with decreasing sputtering pressure. The average transmittances of all of the TiO2 films were almost constant for wavelengths in the range of 900–380nm for GR-varied thin films. The optical transmission edge of the TiO2 films deposited at various sputtering pressure shifts toward low wavelength with higher sputtering pressure. 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 increasing sputtering pressure. However, the photocatalytic efficiency of TiO2 films prepared at different GR did not show any regular dependence. The high photocatalytic activity of the sample prepared with GR=7:3 at sputtering pressure of 0.8Pa was tried to be explained by the effect of surface morphology and pure anatase crystalline phase.

Effects of plasma exposure on structural and optical properties of TiO2 films deposited by off-axis target sputtering

TiO 2 films with thickness of about 800–2300 nm have been reactively deposited on glass-slide substrates at an atmosphere of Ar and O2 mixture, using the off-axis target sputtering method. The maximum deposition rate of the film was 12.8 nm/min. The optical properties and the crystal structure of the films were measured using spectrophotometry, Raman spectroscopy, and x-ray diffractometry, respectively. Most of the films deposited in this study were transparent and had anatase crystal structure, while some of them were semitransparent. The A(101), A(112), A(211) and A(220) peaks were observed in the x-ray diffraction patterns, where A shows the anatase phase of TiO2. With increasing plasma exposure, the x-ray peak intensities IP of A(101) and A(112) gradually decreased, while the IP of A(211) and A(220) gradually increased. The IP depended strongly on the substrate position in this study. Moreover, the A(220) peak was significantly higher than other peaks when the TiO2 crystallites became larger. The anatase phase of the TiO2 films was also revealed in the Raman spectra with a Raman shift of 145 cm−1. With decreasing plasma exposure, the changes in the optical transmittance spectra of TiO2 films were very small at the wavelength of 350–900 nm. However, the transmittance spectra significantly depended on the wavelength with increasing plasma exposure. Consequently, it was found that the crystal structure and the optical properties of as-deposited TiO2 films were strongly affected by plasma exposure during film deposition.

Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films

A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical properties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transformed into single-phase rutile TiO2 at temperatures ⩾ 550 °C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 °C only. An increase in the oxidation temperatures ranging between 700 and 900 °C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (Eg). According to the coherent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen deficiency at a higher oxidation temperature rather than the presence of an amorphous component in the prepared films.

Chemical composition of electron‐beam evaporated TiO2 films

Chemical composition and optical properties of TiO2 films depend on deposition conditions. A detailed investigation has been made on the influence of deposition parameters, such as starting material, substrate temperature, and post deposition heating in air on the chemical composition of TiO2 films deposited by electron‐beam evaporation of TiO and TiO2 in neutral and ionized oxygen. The chemical composition of the films has been analyzed by x‐ray photoelectron spectroscopy and Auger electron spectroscopy. The composition of TiO2 films deposited in neutral oxygen were found to contain lower oxides of titanium in addition to TiO2 whereas films prepared in ionized oxygen were found to be stoichiometric TiO2.

Optical properties of electron-beam evaporated TiO2 films deposited in an ionized oxygen medium

Optical absorption in TiO2 films depends upon starting material and deposition conditions. The influence of the combined effect of substrate temperature and ionized oxygen on the optical properties of TiO2 films deposited by reactive electron beam evaporation of TiO is presented. The ionized oxygen medium reduced the absorption in films considerably. The substrate temperature has only marginal influence on the extinction coefficient of these films. The influence of film thickness on the optical properties of TiO2 films is also studied. The variation in optical properties of TiO2 films has been explained on the basis of enhanced reactivity of oxygen and the decrease of the condensation coefficient of reacting species at elevated substrate temperature.