Time-resolved Microwave Conductivity Studies on the Chemical Treatment of the Nanocrystalline Porous TiO2 Films

Effect of Ti(iso-C3H7O)4 treatment on the photoinduced charge carrier kinetics of nanocrystalline porous TiO2 films is studied by time-resolved microwave conductivity measurements. Analysis of the transient photoconductivity decays indicates that Ti(iso-C3H7O)4 treatment leads to an increased concentration of photogenerated charge carriers and a fast interfacial transfer rate of holes via the surface modification of the freshly growing TiO2 nanocrystallites.

Nanostructure Study of TiO2 Films Prepared by Dip Coating Process

The microstructure properties of the sol-gel derived TiO2 films were studied by the atomic force microscopy (AFM). The films were prepared by dip coating process. The optical properties of the films were explained on the basis of the microstructure of the films.

Photocatalytic Property of TiO2 Films Deposited by Pulsed DC Magnetron Sputtering

TiO2 thin films were prepared by DC magnetron sputtering with the oxygen flow rate higher than the threshold. The film deposited for 5 h was of anatase phase with a preferred orientation along the <220> direction, but the films deposited for 2 and 3 h were amorphous. The transmittance and photocatalytic activity of the TiO2 films increased constantly with increasing film thickness. When the annealing temperature was lower than 700℃, only anatase grew in the TiO2 film. TiO2 phase changed from anatase to rutile when the annealing temperature was above 800℃. The photocatalytic activity decreased with increasing annealing temperature.

Enhanced Photoelectric Property of Mo-C Codoped TiO2 Films Deposited by RF Magnetron Cosputtering

Mo-C codoped TiO2 films were prepared by RF magnetron cosputtering. Ultraviolet-visible spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray Analysis and X-Ray Diffraction were used to study the influences of codoping on energy gap, surface morphology, valence states of elements, ions content and crystal structure, respectively. The concentration of photogenerated carriers was measured by studying photocurrent density, while catalytic property was evaluated by observing degradation rate of methylene blue under visible light. A Mo-doped TiO2 film, whose content of Mo had been optimized in advance, was prepared and later used for subsequent comparisons with codoped samples. The result indicates that Mo-C codoping could curtail the energy gap and shift the absorption edge toward visible range. Under the illumination of visible light, codoped TiO2 films give rise to stronger photocurrent due to smaller band gaps. It is also found that Mo, C codoping results in a porous surface, whose area declines gradually with increasing carbon content. Carbon and Molybdenum doses were delicately optimized. Under the illumination of visible light, sample doped with 9.78at% carbon and 0.36at% Mo presents the strongest photocurrent which is about 8 times larger than undoped TiO2 films, and about 6 times larger than samples doped with Mo only.

Preparation of TiO2 and SiC Films from Their Precursors Using Electrospraying

Titanium dioxide(TiO2) films were prepared by cone - jet mode electrospraying a titanium ethoxideprecursor solution onto a silicon substrate.The effects of spraying time,substrate temperature and aging on thesurface morphology of the films prepared were studied.Thin films obtained after spraying for 600 s were aged atroom temperature to form a porous TiO2 network with pores in the size range of 100 - 500 nm.Thicker filmswere prepared by spraying for 3 000 s,but these cracked on drying although it can be concluded that films pre-pared using a higher substrate temperature were denser.By this method,SiC coating was also prepared on anAl2O3 substrate using polysilane as a precursor.The result implies the potential of an industrial production ofdye sensitized solar cells by electrospraying technique.

Inverted organic solar cells with solvothermal synthesized vanadium-doped TiO2 thin films as efficient electron transport layer

We investigated the effects of using different thicknesses of pure and vanadium-doped thin films of TiO2 as the electron transport layer in the inverted configuration of organic photovoltaic cells based on poly（3-hexylthiophene） P3HT：[6-6] phenyl-（6） butyric acid methyl ester（PCBM）. 1% vanadium-doped TiO2nanoparticles were synthesized via the solvothermal method. Crystalline structure, morphology, and optical properties of pure and vanadium-doped TiO2 thin films were studied by different techniques such as x-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and UV–visible transmission spectrum. The doctor blade method which is compatible with roll-2-roll printing was used for deposition of pure and vanadium-doped TiO2 thin films with thicknesses of 30 nm and 60 nm. The final results revealed that the best thickness of TiO2 thin films for our fabricated cells was 30 nm. The cell with vanadium-doped TiO2 thin film showed slightly higher power conversion efficiency and great Jsc of 10.7 mA/cm^2 compared with its pure counterpart. In the cells using 60 nm pure and vanadium-doped TiO2 layers, the cell using the doped layer showed much higher efficiency. It is remarkable that the external quantum efficiency of vanadium-doped TiO2 thin film was better in all wavelengths.

Effect of Annealing Temperatures on the Structural and Electrical Properties of Laser Induced Plasma for TiO2x-1Bix Thin Films

In this study, Bismuth doped Titanium dioxide thin films were deposited on glass substrates by a pulse laser deposition using laser. The effect of annealing temperature on the structural and electrical properties was investigated. X-ray diffraction pattern for pure and doped titanium dioxide films with different doping different ratio with Bi show that these films have amorphous structure oanvert to polycrystalline structure with annealing and doping and have a good identically with standard peaks for Anatase and Rutile phases. The orientation was at specific direction for Rutile. The crystalline of films increases by the increase of doping ratio. The crystalline increased with annealing temperature. Annealed films at different annealing temperatures have been studied. The results show that these films have two activation energies and by increasing the doping ratio, the activation energies and the conductivity increase. Both the annealing and composition effects on Hall constant, density of electron carders and Hall mobility are studied. Hall Effect measurements show that all films have n- type charge conductivity and the concentration increases while the mobility decreases with doping and annealing.

TiO2-Loaded WO3 Composite Films for Enhancement of Photocurrent Density

Titanium dioxide （TiO2） loaded tungsten trioxide （WO3） composite films are prepared by an E-beam vapor system. Associated with the existence of a heterojunction at the interface of TiO2 and WO3, the prepared TiO2-WO3 composite film shows enhanced photocurrent density, four times than the pure WO3 film illuminated under xenon lamp, and higher incident-photon-to-current conversion e^ciency. By varying the initial TiO2 film thickness, such composite structures could be optimized to obtain the highest photocurrent density. We believe that thin TiO2 films improve the light response and increase the surface roughness of WO3 films. Furthermore, the existence of the heterojunction results in the e^cient charge carriers＇ separation, transfer process, and a lower recombination of electron-hole pairs, which is beneficial for the enhancement of photocurrent density.

Electrophoretic Deposition of TiO2/Nb2O5 Composite Electrode Thin Films for Photovoltaic Application

Nano sized powders of TiO2 （titanium dioxide） and Nb2O5 （Niobium （V） oxide） were used to fabricate TiO2/Nb2O5 composites thin films by EPD （electrophoretic deposition） technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR spectrophotometer spectra. The highest （55%） transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC （direct current） voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM （scanning electron microscope） micrographs of the composite electrode thin films showed that porous films of high quality with well controlled morphology were deposited by using the EPD technique.

Characterization and photoelectrochemical performance of Zn-doped TiO_2 films by sol-gel method

Zn-doped TiO2 (Zn?TiO2) thin films were prepared by the sol?gel method on titanium substrates with heat treatment at different temperatures. The effects of heat treatment temperatures and Zn doping on the structure, photocathodic protection and photoelectrochemical properties of TiO2 thin films were investigated. It is indicated that the photoelectrical performance of the Zn?TiO2 films is enhanced with the addition of Zn element compared with the pure-TiO2 film and the largest decline by 897 mV in the electrode potential is achieved under 300 °C heat treatment. SEM?EDS analyses show that Zn element is unevenly distributed in Zn?TiO2 films; XRD patterns reveal that the grain size of Zn?TiO2 is smaller than that of pure-TiO2; FTIR results indicate that Zn - O bond forms on Zn?TiO2 surface. Ultraviolet visible absorption spectra prove that Zn?TiO2 shifts to visible light region.Mott?Shottky curves show that the flat-band potential of Zn?TiO2 is more negative and charge carrier density is bigger than that ofpure-TiO2, implying that under the synergy of the width of the space-charge layer, carrier density and flat-band potential, Zn?TiO2 with 300 °C heat treatment displays the best photocathodic protection performance.

Doped-TiO_2 Photocatalysts and Synthesis Methods to Prepare TiO_2 Films

TiO2 is a promising photocatalyst. However, the low photocatalytic efficiency calls for the modification of TiO2. Metal- and nonmetal-doping of TiO2 have been proved to be effective ways to enhance photocatalytic properties. This review provides a deep insight into the understanding of the metal- and nonmetal-doped TiO2 photocatalysts. This article begins with the introduction of the crystal structures of TiO2 and applications of TiO2 materials. We then reviewed the doped-TiO2 system in two categories： （1） metal-doped TiO2 photocatalysts system, and （2） nonmetal-doped TiO2 photocatalysts system. Both experimental results and theoretical analyses are elaborated in this section. In the following part, for the advantages of TiO2 thin films over particles, various preparation methods to obtain TiO2 thin films are briefly discussed. Finally, this review ends with a concise conclusion and outlook of new trends in the development of TiO2-based photocatalysts.

Structural and optical properties of nano-spin coated sol-gel porous TiO_2 films

Three thicknesses of TiO2 films, 174, 195, and 229 nm, were deposited onto quartz substrates by sol–gel spin coating method. The as-deposited thin films were characterized by nano-crystallite with different sizes (19–46 nm) and relatively high porous structure. Optical constants were determined and showed the lowest refractive index of 1.66 for the as-prepared films that ever reported till now. Obtained results were discussed through current theoretical ideas.

Fabrication of nanoporous TiO_2 films with novel surface morphology on conducting glass(FTO) substrate

The crystalline structure and surface morphology of TiO2 semiconductor coating play an important role in the conversion efficiency of dye-sensitized solar cells. In order to obtain TiO2 coating with controllable morphology and high porosity, nanoporous TiO2 films were fabricated on conducting glass （FTO） substrates, Ti thin films （1.5-2 gin） were deposited on conducting glass （FTO） substrates via the DC sputtering method, and then electrochemically anodized in NH4F/ethylene glycol solution. The crystalline structure and surface morphology of the samples were characterized by X-ray diffraction （XRD） and field emission scanning electron microscopy （FESEM）, respectively. The influences of anodizing potential, electrolyte composition, and pH value on the surface morphology of nanoporous TiO2 films were extensively studied. The growth mechanism of nanoporous TiO2 films was discussed by current density variations with anodizing time. The results demonstrate that nanoporous TiO2 films with high porosity and three-dimensional （3D） networks are observed at 30 V, when the NH4F concentration in ethylene glycol solution is 0.3% （mass fraction） and the electrolyte pH value is 5.0.

Preparation and Enhanced Daylight-Induced Photo-Catalytic Activity of Transparent C-Doped TiO_2 Thin Films

The transparent C-doped TiO2 nanostructure films were fabricated on the silicate glass substrates by sol-gel spin-coated method. The as-prepared films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, UV-visible absorption spectra （UV-vis） and X-ray photoelectron spectroscopy （XPS）. The photocatalytic activity was evaluated via the photocatalytic oxidation of methylene blue in aqueous under daylight irradiation at room temperature. The results show that the daylight-induced photocatalytic activities of the as-prepared films are improved by the C-doping. The calcination temperatures significantly affect the morphology, microstructure and photocatalytic activity of the as-prepared samples. At 723 K, the C-doped TiO2 films exhibit the highest photocatalytic activity due to the synergetic effects of good crystallization, appropriate oxygen vacancies and strong absorption in the near UV and visible-light region.

Photoelectric properties of thin Eu^(3+)-doped TiO_2 films sensitized by cis-RuL_2(SCN)_2·2H_2O

Thin nanocrystalline TiO2 films doped by europium ions (Eu3+) were obtained by the sol-gel method. The photoelectric properties of Eu3+-doped TiO2 film electrode sensitized by cis-RuL2(SCN)2·2H2O (L=cis-2,2′-bipyridine-4,4′-dicarboxlic acid) ruthenium complex were studied. The thin films were characterized by X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy. Effect of doping Eu3+ on microscopic structure and photoelectrical properties were discussed. The result shows that doping europium ions makes specific surface area of these films larger, which contributes to improving the photoelectric properties. It is found that an optimal composition doped with 0.2 mol.% Eu3+ exhibits the highest photoelectric properties. Isc is 0.37 mA·cm-2, which is 0.17 mA·cm-2 bigger than that of un-doped films; Voc is 405 mV, which is 50 mV bigger than that of un-doped films.

Preparation,structure and ferromagnetic properties of the nanocrystalline Ti_(1-x)Mn_xO_2 thin films grown by radio frequency magnetron co-sputtering

This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.

Formation Mechanistism Study of TiO2 Film Comprising Nanotubes and Nanoparticles

A novel titanium dioxide （TiO2） film comprising both nanotubes and nanopaticles was fabricated by an anodization process of the modified titanium. The local electric field at the anodized surface was simulated and its influence on the morphology of the TiO2 film was discussed. The results show that the electric field strength is enhanced by the covering. The growth rate of TiO2 increases with the assist of the local electric field. However, TiO2 dissolution is hindered since the local electric field prevents [TiF6]6- from diffusing. It means that the balance condition for the formation of nanotubes is broken, and TiO2 nanoparticles are formed. Moreover, the crystal structure of the TiO2 film was confirmed using X-ray diffraction and Raman analysis. The anatase is a main phase for the proposed film.

Influence of Annealing Temperature on the Properties of TiO_2 Films Annealed by ex situ and in situ TEM

TiO2 thin films were deposited on quartz substrates by DC reactive magnetron sputtering of a pure Ti target in Ar/O2 plasma at room temperature. The TiO2 films were annealed at different temperatures ranging from 300 to 800 ℃ in a tube furnace under flowing oxygen gas for half an hour each. The effect of annealing temperatures on the structure, optical properties, and morphologies were presented and discussed by using X-ray diffraction, optical absorption spectrura, and atomic force microscope. The films show the presence of diffraction peaks from the （101）, （004）, （200） and （105） lattice planes of the anatase TiO2 lattice. The direct band gap of the annealed films decreases with the increase of annealing temperature. While, the roughness of the films increases with the increases of annealing temperature, and some significant roughness changes of the TiO2 film surfaces were observed after the annealing temperature reached 800 ℃. Moreover, the influences of annealing on the microstructures of the TiO2 film were investigated also by in situ observation in transmission electron microscope.

Atomic Force Microscopy Studies on the Chemical Treatment of Nanocrystalline Porous TiO_2 Films

AFM has been utilized to study the surface topography and the local conductivity of nanocrystalline TiO2 films. Improving the local conductivity by Ti(iso-C3H7O)4 treatment is characterized by quantitative analysis of the simultaneous current image. The mechanism of Ti(iso C3H7O)4 treatment is discussed.