Structural, electrical and optical properties of ITO films with a thin TiO2 seed layer prepared by RF magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited by RF magnetron sputtering on TiO₂-coated glass substrates (the TiO₂ layer is usually called seed layer). The properties of ITO films prepared at a substrate temperature of 300 °C on bare and TiO₂-coated glass substrates have been analyzed by using X-ray diffraction, atomic force microscope, optical and electrical measurements. Comparing with single layer ITO film, the ITO film with a TiO₂ seed layer of 2 nm has a remarkable 41.2% decrease in resistivity and similar optical transmittance. The glass/TiO₂ (2 nm)/ITO film achieved shows a resistivity of 3.37 × 10⁻⁴ Ω cm and an average transmittance of 93.1% in the visible range. The glass/TiO₂ may be a better substrate compared with bare glass for depositing high quality ITO films.     

Preparation of anatase TiO2 thin films by vacuum arc plasma evaporation

Anatase titanium dioxide (TiO₂) thin films with high photocatalytic activity have been prepared with deposition rates as high as 16 nm/min by a newly developed vacuum arc plasma evaporation (VAPE) method using sintered TiO₂ pellets as the source material. Highly transparent TiO₂ thin films prepared at substrate temperatures from room temperature to 400 °C exhibited photocatalytic activity, regardless whether oxygen (O₂) gas was introduced during the VAPE deposition. The highest photocatalytic activity and photo-induced hydrophilicity were obtained in anatase TiO₂ thin films prepared at 300 °C, which correlated to the best crystallinity of the films, as evidenced from X-ray diffraction. In addition, a transparent and conductive anatase TiO₂ thin film with a resistivity of 2.6 × 10^− 1 Ω cm was prepared at a substrate temperature of 400 °C without the introduction of O₂ gas.     

Photocatalytic performance of TiO2 films produced with combination of oxygen-plasma and rapid thermal annealing

In this work, a combination of oxygen plasma and rapid thermal annealing was suggested in order to oxidize the surface of titanium into TiO₂. A plasma was formed by employing pure oxygen at 150 W, 300 W, and 400 W under a pressure of 7.5 to 8.5 Pa for 5 to 10 min. The TiO₂ was then subjected to rapid thermal annealing (RTA) at a temperature of 400 to 500 °C for 1 min. From the attained results, an RF power of 300 W for 5 min was observed to be sufficient to produce an optimal photocatalytic TiO₂ film. Optimal conditions were confirmed by additional experiments involving humic acid (HA) degradation of the TiO₂ films. When compared to a traditional TiO₂ film, a TiO₂ film prepared with an oxygen-plasma treatment and RTA system exhibited improved photocatalytic capability for HA photodegradation in an aqueous solution. Therefore, this process proposed in this work can be an excellent alternative to the traditional method for fabricating photocatalytic TiO₂ films.     

Highly-ordered mesoporous titania thin films prepared via surfactant assembly on conductive indium-tin-oxide/glass substrate and its optical properties

Highly ordered mesoporous titanium dioxide (titania, TiO₂) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO₂ buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO₂ buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO₂-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO₂ buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO₂ film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO₂ (~ 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications.     

Photocatalytic properties of Cr-doped TiO2 films prepared by oxygen cluster ion beam assisted deposition

We prepared Cr-doped titanium dioxide (TiO₂) films by oxygen (O₂) cluster ion beam assisted deposition method, and investigated photocatalytic properties of the films as well as crystallographic property, optical property and surface morphology. The films prepared at a substrate temperature below 200 °C were found to be amorphous from the X-ray diffraction measurement. For the substrate temperatures such as 300 °C and 400 °C, the films exhibited rutile and/or anatase structures. The film surface measured by the atomic force microscope (AFM) was smooth at an atomic level. Furthermore, the optical band gap decreased with increase of Cr-composition, and it was approximately 3.3 eV for the non-doped films, 3.2 eV for the 1% Cr-doped films and 3.1 eV for the 10% Cr-doped films, respectively. With regard to the photocatalytic properties of the Cr-doped TiO₂ films, we measured the change of contact angle as well as the photocatalytic degradation of methylene blue by the UV light irradiation. Compared with the non-doped films, the 1% Cr-doped films prepared at a substrate temperature of 400 °C showed high degradation efficiency. In addition, the contact angle of the 1% Cr-doped films with an initial value of 60° decreased to 10° by the UV light irradiation for 20 min, and the films exhibited the predominant properties of photocatalytic hydrophilicity even for the UV light irradiation with longer wavelengths.     

Photocatalytic activities of TiO2 thin films prepared on Galvanized Iron substrate by plasma-enhanced atomic layer deposition

Titanium dioxide (TiO₂) thin films were prepared on Galvanized Iron (GI) substrate by plasma-enhanced atomic layer deposition (PE-ALD) using tetrakis-dimethylamido titanium and O₂ plasma to investigate the photocatalytic activities. The PE-ALD TiO₂ thin films exhibited relatively high growth rate and the crystal structures of TiO₂ thin films depended on the growth temperatures. TiO₂ thin films deposited at 200 °C have amorphous phase, whereas those with anatase phase and bandgap energy about 3.2 eV were deposited at growth temperature of 250 °C and 300 °C. From contact angles measurement of water droplet, TiO₂ thin films with anatase phase and Activ™ glass exhibited superhydrophilic surfaces after UV light exposure. And from photo-induced degradation test of organic solution, anatase TiO₂ thin films and Activ™ glass decomposed organic solution under UV illumination. The anatase TiO₂ thin film on GI substrate showed higher photocatalytic efficiency than Activ™ glass after 5 h UV light exposure. Thus, we suggest that the anatase phase in TiO₂ thin film contributes to both superhydrophilicity and photocatalytic decomposition of 4-chlorophenol solution and anatase TiO₂ thin films are suitable for self-cleaning applications.     

Photocatalysis and characterization of the gel-derived TiO2 and P-TiO2 transparent thin films

The gel-derived TiO₂ and P-TiO₂ transparent films coated on fused-SiO₂ substrates were prepared using a spin-coating technique. Effects of phosphorus dopants and calcination temperature on crystal structure, crystallite size, microstructure, light transmittance and photocatalytic activity of the films were investigated. By introducing P atoms to Ti-O framework, the growth of anatase crystallites was hindered and the crystal structure of anatase-TiO₂ could withstand temperature up to 900 °C. The photocatalytic activities of the prepared films were characterized using the characteristic time constant (τ) for the photocatalytic reaction. The titania film with a smaller τ value possesses a higher photocatalytic ability. After exposing to 365-nm UV light for 12 h, the P-TiO₂ films calcined between 600 °C and 900 °C can photocatalytically decomposed ≥ 84 mol% of the methylene blue in water with corresponding τ ≤ 7.1 h, which were better than the pure TiO₂ films prepared at the same calcination temperature.     

Ion beam modification of TiO2 films prepared by Cat-CVD for solar cell

The effects of nitrogen ion bombardment on TiO₂ films prepared by the Cat-CVD method have been studied to improve the optical and electrical properties of the material for use in Si thin film solar cells. The refractive index n and the dark conductivity of the TiO₂ film increased with irradiation time. The refractive index n of the TiO₂ film was changed from 2.1 to 2.4 and the electrical conductivity was improved from 3.4 × 10^− 2 to 1.2 × 10^− 1 S/cm by the irradiation. These results are due to the formation of Ti-N bonds and oxygen vacancies in the film.     

A simple electrophoretic deposition method to prepare TiO2-B nanoribbon thin films for dye-sensitized solar cells

This paper describes a simple method utilizing electrophoretic deposition (EPD) to quickly synthesize hydrogen titanate nanoribbon films. The subsequent heating of the hydrogen titanate nanoribbon films causes the dehydration of interlayered OH groups, thereby leading to TiO₂-B nanoribbon films. Thick, uniform TiO₂-B nanoribbon films were obtained from prepared alkali suspensions. The crystal structure of the hydrogen titanate and TiO₂-B nanoribbon films obtained from EPD underwent analysis by X-ray diffraction and high-resolution transmission electron microscope. EPD controlled the thickness of TiO₂-B nanoribbons films. TiO₂-B-coated fluorine-doped tin oxide films were dye-sensitized with N3 and used as a photoanode in an electrochemical solar cell. The solar cell yielded conversion efficiencies of 0.87% for an incident solar energy of 100 mW/cm².     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Characterization of TiO2 thin films prepared by electrolytic deposition for lithium ion battery anodes

The electrolytic deposition of TiO₂ thin films on platinum for lithium batteries is carried out in TiCl₄ alcoholic solution and the films are subsequently annealed. The as-prepared films are amorphous TiO(OH)₂·H₂O, transformed into anatase TiO₂ at 350 °C, and then gradually into rutile TiO₂ at 500 °C. Cyclic voltammograms show oxidation and reduction peaks at 2.20 and 1.61 V, respectively, corresponding to charge and discharge plateaus at 1.98 and 1.75 V vs. Li⁺/Li. The specific capacity decreases with increasing current density for film of 128-nm thickness in the initial discharge. It is observed that the diffusion flux of Li⁺ insertion/extraction into/from TiO₂ controls the reaction rate at higher current densities. Consequently, at low film thickness, high discharge capacity (per weight) is found for the initial cycle at a current density of 10 μA cm^− 2. However, the capacity of prepared films in various thicknesses approach 103 ± 5 mAh g^− 1 after 50 cycles, since the formation of cracks for thicker films offers shorter diffusion paths for Li⁺. In addition, TiO₂ films show electrochromic properties during lithiation and delithiation.     

Glancing angle deposited titania films for dye-sensitized solar cells

A series of sculptured porous nano-columnar titanium oxide films were prepared by glancing angle deposition (GLAD) method using an electron-beam evaporation system. The films were deposited on ITO glasses at various incident angles from 53° to 86°and used as photoanode in a dye-sensitized solar cell (DSSC). The as-deposited TiO₂ films are comprised of helical nano-columns and assembled in an orderly manner with gaps or pores in between. The porous nanostructured films provide a synergetic effect of high surface area, effective route for electron transfer, tight interfaces, and enhanced light trapping, which are all beneficial for higher cell efficiency. The DSSCs incorporated with the GLAD films of 4 μm thick exhibited a high fill factor (FF) up to 0.77. The TiO₂ film deposited at an incident angle of 73° provides the largest internal surface area and the largest amount of dye absorption and results in the highest light conversion efficiency of 2.78%.     

Titanium dioxide thin films prepared by electrolysis from aqueous solution of titanium-lactic acid complex for dye-sensitized solar cells

Titanium oxide (TiO_x) thin films were prepared on transparent conducting substrate (fluorine-doped tin oxide) by cathodic electrolysis of a solution containing a titanium bis(ammonium lactato)dihydroxide and an ammonium nitrate at 323 K. Post-deposition treatment: calcination at 723 K or hot-water treatment at > 363 K promoted the growth of an anatase type crystalline phase in the TiO₂ thin film, as evidenced by X-ray diffraction and X-ray photoelectron spectroscopy. The calcined films were used as electrodes of a dye-sensitized solar cells and the cells' energy conversion efficiency was comparable to that obtained with commercially available TiO₂ nanoparticle electrodes.     

Preparation of Ba–Ti–O films by laser chemical vapor deposition

Ba–Ti–O films were prepared on Pt-coated Si substrate by laser chemical vapor deposition, and their orientations and microstructures were compared. Ba₂TiO₄, BaTiO₃, BaTi₂O₅, Ba₄Ti₁₃O₃₀ and BaTi₄O₉ single-phase films were prepared at Ti to Ba molar ratio from 0.41 to 3.49. The α′-Ba₂TiO₄ film showed (0 1 0) and (0 9 1) co-orientation with elongated, truncated columnar grains. The BaTiO₃ film was composed of triangular and hexagonal grains with slight (1 1 1) orientation. The BaTi₂O₅ film had (0 1 0) orientation and faceted columnar grains. The Ba₄Ti₁₃O₄₀ film showed (1 0 0) and (0 1 2) co-orientation with shellfish-like grains. The BaTi₄O₉ film showed (0 1 0) orientation with slightly rounded faceted columnar grains. The deposition rates of Ba–Ti–O films ranged from 30 to 144 μm h⁻¹.     

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO₂ thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO₂. Films calcined in argon or in low vacuum (∼2 × 10⁻¹ mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of ∼300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO₂ films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range ∼200-300 nm, band gap energy and crystallite size of TiO₂ films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO₂ films may be tailored during calcination period.     

Rapid erasing of wettability patterns based on TiO2-PDMS composite films

TiO₂-polydimethylsiloxane (TiO₂-PDMS) composite films are prepared using the sol–gel method from a Ti(OBu)₄–benzoylacetone solution containing PDMS. The prepared films are cured by irradiation with ultraviolet (UV) light. Structural changes in the films after UV irradiation are confirmed by UV–vis absorption experiments, which show that an absorption band characteristic of the benzoylacetonate chelate rings disappears. This finding is ascribed to structural changes associated with the dissociation of the chelate rings. The IR spectra of the thin films exhibit a broad absorption band after UV irradiation, indicating that a Ti–O–Ti network forms in the thin film. Contact angles are measured for the TiO₂-PDMS thin films, showing wettability conversion from hydrophobic to superhydrophilic states by irradiation with oxygen plasma for 1 s. This phenomenon is explained by XPS experiments which reveal that the number of carbon atoms decreases, whereas the number of oxygen atoms increases on the surface of the TiO₂-PDMS composite films. Finally, hydrophobic–superhydrophilic patterns are fabricated based on a patterned TiO₂-PDMS composite film. The film displays a rapid change to superhydrophilicity over the whole film surface upon plasma irradiation for 1 s, which means that the wettability patterns are rapidly erasable.     

Superhydrophilicity of TiO2 thin films using TiCl4 as a precursor

TiO₂ thin films on soda lime glass were prepared by the sol-gel method and spin coating process using TiCl₄ as a precursor. The AFM images indicate that the surface morphology of the films is granular with 72 nm particle size. The roughness and thickness of the films are about 3 nm and 140 nm, respectively. The XRD spectrum shows polycrystalline anatase phase without any considerable impurity phase. The UV-vis spectroscopy of the films show 80-90% transmission in the visible region. The absorption edge is at 370 nm, which corresponds to 3.3 eV energy band gap. The films have a high superhydrophilicity character after being exposed to UV illumination for about 10 min. The surfaces, which were synthesized by this method, can retain their superhydrophilicity property for at least 24 h. Our results are consistent with the idea that UV-induced wetting of TiO₂ surface is caused by the removal of hydrophobic layers of hydrocarbons by TiO₂-mediated photooxidation, which leads to the attractive interaction of water with clean TiO₂ surface. TiO₂ thin films on Si(1 1 1), Si(1 0 0), and quartz substrates need less time than glass and polycrystalline Si substrates to be converted to superhydrophilic surface.     

Fabrication of TiO2 nanotube film by well-aligned ZnO nanorod array film and sol-gel process

High density TiO₂ nanotube film with hexagonal shape and narrow size distribution was fabricated by templating ZnO nanorod array film and sol-gel process. Well-aligned ZnO nanorod array films obtained by aqueous solution method were used as template to synthesize ZnO/TiO₂ core-shell structure through sol-gel process. Subsequently, TiO₂ nanotube array films survived by removing the ZnO nanorod cores using wet-chemical etching. Polycrystalline anatase TiO₂ nanotube films were ∼ 1.5 μm long and ∼ 100 nm in inter diameter with a wall thickness of ∼ 10 nm.     

Photocatalytic Zn-doped TiO2 films prepared by DC reactive magnetron sputtering

Zn-doped TiO₂ films were prepared by means of pulsed DC reactive magnetron sputtering method using Ti and Zn mixed target. The deposition condition was optimized to produce uniform and transparent TiO₂ films. Titanium was in the Ti⁴⁺ oxidation state in all Zn-doped TiO₂ films. The zinc oxide deposited on the substrate was in the fully oxidized state of ZnO. Increase of zinc concentration inhibited the crystal growth in the TiO₂ films. The surface morphology gradually changed from crystalline to amorphous along with the increase of doped zinc concentration. The optical transmittances of these films decreased only slightly with increasing zinc concentration due to very similar band edges of ZnO and anatase TiO₂. The doped ZnO had weak influence on light absorption of the TiO₂ films. When zinc concentration was very low (<1 at%), the photocatalytic activities of the doped films had nearly no difference from that of pure TiO₂ film. Photocatalytic activities decreased obviously in the films containing high amount of zinc oxide.     

Low temperature preparation of TiO2 nanodot film on substrates

Herein, we report a photoinduced transition of hydrophobicity to high hydrophilicity of TiO₂ nanodot films in applications of cell sheet engineering. A phase-separation-induced self-assembly process was adopted to prepare a TiO₂ nanodot gel film on a substrate. Subsequently, a hydrothermal treatment (with ethanol/water at 140 °C for 2 h) was used to convert the nanodot gel film to TiO₂ nanodot solid film. The resulting TiO₂ dots were amorphous with adjustable size and density. The amorphous TiO₂ nanodot film showed a conversion from a good hydrophobic surface, with a water contact angle (WCA) of 67.6 ± 2.0°, to a highly hydrophilic one, with a WCA of 5.3 ± 2.0° (i.e. almost superhydrophilic) after UV irradiation. A good reversibility was also observed.