Surface properties of doped and undoped TiO2 thin films deposited by magnetron sputtering

In this work, transparent titanium dioxide (TiO₂) thin films were deposited onto microscope glass slides by means of the d.c. reactive magnetron sputtering method. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectroscopy (UV) and contact angle analysis using the Owens-Wendt method for the surface energy calculation. The photocatalytic activity of the films was tested by measuring the photodegradation of Rhodamine-B (RhB) dye under radiation of UV light. Iron-doped TiO₂ films were also prepared in order to study the Fe-doping effect on TiO₂ photocatalytic activity. The influences of different iron concentrations on the contact angle of the series of Fe-doped TiO₂ thin films, were investigated. The influences of total sputtering pressures on TiO₂ photocatalytic activity were also investigated. It was observed that the photocatalytic activity of the TiO₂ thin films was slightly improved by increasing the total sputtering pressure. Moreover, it was also observed that in general, iron-doping was detrimental for photocatalytic activity, nevertheless the films with low iron concentrations showed better photocatalytic activity than those with high iron concentrations. It was found that iron-doping has changed the wettability appetency of TiO₂ coated surfaces.     

Study of Nd-doping effect and mechanical cracking on photoreactivity of TiO2 thin films

Pure and Nd-doped TiO₂ thin films were fabricated by reactive d.c. magnetron sputtering at low-temperature from a pure Ti target. The structure of films was analyzed by X-ray diffraction (XRD). In order to study the Nd-doping effect on TiO₂ photocatalytic activity, some films were deposited on microscope glass substrates under a constant total sputtering pressure and using different Nd-doping concentrations. The effect of different Nd-dopant concentrations and its influence on the photocatalytic efficiency has been explored by measuring the photodegradation of rhodamine-B (RhB) aqueous solution under radiation of UV light. It is principally that for comparison between heat treatment and doping process on TiO₂ photocatalytic efficiency (important under the point of view of energy costs related with industrial sputtering techniques), crystalline TiO₂ films were also produced by thermal annealing. It was found that comparing with annealed pure TiO₂ films, Nd-doping do not improve the photocatalytic activity. At the same time, it was observed that there seems to exist a dopant concentration band for optimal photoreactivity. In order to study the effect of the film mechanical strength on photocatalytic activity, fragmentation tensile tests were also done on TiO₂/PET (polyethylene terephthalate) substrates at increasing applied strains. It was found that increasing the magnitude of the applied tensile strain, pure TiO₂ becomes more photocatalytic efficient.     

Enhanced photocatalytic activity of silver nanoparticles modified TiO2 thin films prepared by RF magnetron sputtering

Ag-TiO₂ nanostructured thin films with silver volume fraction of 0–40% were prepared by RF magnetron sputtering. The microstructure, surface topography, and optical properties of the films were characterized by X-ray diffractometer, transmission electron microscope, and ultraviolet–visible spectrophotometer. Photocatalytic activity of the films was evaluated by light-induced degradation of methyl orange (C₁₄H₁₄N₃NaO₃S) solution using a high pressure mercury lamp as lamp-house. The relation of photocatalytic activity and silver content was studied in detail. It is found that silver content influences microstructure of TiO₂ thin films, and silver in the films is metallic Ag (Ag⁰). Photocatalytic activity of the films increases with increasing silver content up to 5 vol.% Ag and then decreases to values significantly still bigger than that of pure TiO₂ thin films. Silver nanoparticles significantly enhance the photocatalytic activity of TiO₂ films. The better separation between electrons and holes on silver modified TiO₂ thin films surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the decrease of energy gap of the films and the increase of oxygen anion radicals O₂⁻ and reactive center of surface Ti³⁺ on silver modified TiO₂ thin films surface.     

The effect of argon pressure on the structural and photocatalytic characteristics of TiO2 thin films deposited by d.c. magnetron sputtering

TiO₂ thin films of 200-300 nm thickness were deposited by d.c. magnetron sputtering onto glass substrates from a semiconducting TiO_2−x target in pure Ar using pressures between 0.1 and 1.0 Pa. The obtained TiO₂ coatings are transparent and have refractive indices between 2.5 and 1.9. Post deposition heat treatment at different temperatures was performed to achieve crystallization of anatase TiO₂. The as-deposited and heat treated films were examined with UV-VIS (transmission), SEM and XRD to investigate the influence of the argon pressure during deposition on the structural development during heat treatment. Additionally, the photocatalytic activity of the films was tested by measuring the decomposition rate of ethanol in a controlled gas atmosphere simulating air, and was related to their respective microstructures.     

Study of the deposition parameters and Fe-dopant effect in the photocatalytic activity of TiO2 films prepared by dc reactive magnetron sputtering

The reactive magnetron sputtering method was used to prepare pure and Fe-doped titanium dioxide thin films. The films were deposited onto microscope glass slides and polycarbonate plates at different total pressure and Fe-doping concentrations. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible spectroscopy (UV). For glass substrates a polycrystalline TiO₂ structure was verified with X-ray diffraction, which showed typical characteristic anatase reflections. An iron phase appeared in the highly Fe-doped samples. The absorption edges of the Fe-doped TiO₂ films shifted to visible region with increasing concentration of iron. For the polycarbonate substrate an amorphous TiO₂ structure was revealed for all deposition conditions. The effects of different Fe-doping and total pressure levels on the photocatalytic activity were obtained by the degradation rates of Rhodamine-B (RoB) dye under UV light irradiation. For the deposition conditions considered in this study the highest photodegradation rates were achieved for films deposited on the polymer substrates. Of these overall highest rates was achieved for deposition at 0.4 Pa and without doping. However, for both substrates, films prepared at the particular total pressure of 0.5 Pa and a low iron concentration showed better photocatalytic activity than the pure TiO₂ films prepared under the same deposition parameters. On the contrary, the photocatalytic degradation rates of RoB on the highly Fe-doped TiO₂ films decreased strongly.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

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.     

Photodecomposition and bactericidal effects of TiO2 thin films prepared by a magnetron sputtering

TiO₂ thin films were deposited on either glass or Si wafer substrate using a reactive magnetron sputtering by varying the process conditions including O₂/(Ar+O₂) ratio, working pressure, sputtering time and dc power, to examine the influence of surface morphology and crystallinity on photodecomposition efficiency of phenol and bactericidal activity of Escherichia coli (E. coli 078). The UV illuminated nanoporous anatase TiO₂ films with a higher roughness (205 Å) and crystallinity behaved as the best photocatalysts by 60% of phenol photodecomposition and 70% of bacteria cell (E. coli) destruction. Therefore, it was conceivable that the photocatalytic efficiency may be governed by the specific surface area, which was directly related to the crystallinity and the roughness of the films.     

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.     

Mesoporous TiO2 thin films embedded with Au nanoparticles for the enhancement of the photocatalytic properties

Mesoporous TiO₂ thin films were prepared by hydrothermal-oxidation of titanium metal thin films, which were obtained by DC magnetron sputtering technique. Gold nanoparticles, which were prepared by reduction of HAuCl₄, were embedded into the holes of the mesoporous TiO₂ films by capillary method followed by annealing in air up to 400 °C. The size of pore of TiO₂ films is about 100 nm and that of Au nanoparticles is about 10 nm in average. The morphology of the films was analyzed by field emission scanning electron microscope (FE-SEM) and scanning probe microscopes (SPMs). Subsequently, the photocatalytic performances of the obtained nanosystems in the decomposition of methylene blue solution are discussed. The obtained results show that the dispersion of Au nanoparticles on the mesoporous TiO2 matrix will help enhancing the photocatalytic activity with respect to pure TiO₂ under visible light irradiation.     

Photocatalytic TiO2 films deposited on cenosphere particles by pulse magnetron sputtering method

In the present study, TiO₂ films were deposited on the surface of cenosphere particles using the modified magnetron sputtering equipment under different working conditions. The resulting films were characterized by field emission scanning electron microscopy (FE-SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The FE-SEM and AFM results show that the grain sizes and root-mean-square (RMS) roughness values of the TiO₂ films increase with the increase in deposition time and film thickness. The XRD results indicate that the film was TiO₂ film and sputtering time is an importance condition to influence the films crystal. With the increasing of sputtering time, the crystallization of the TiO₂ film was increased. The XPS results show that only TiO₂ films existed on the surface of cenosphere particles. In addition, the photocatalytic activities of these films were investigated by degrading methyl orange under UV irradiation. The results suggest that the photocatalytic activity of cenosphere particles with anatase TiO₂ films is remarkable and this catalyst can be applicable for the photocatalytic degradation of other organic compounds under UV lights.     

Ag surfactant effects of TiO2 films prepared by sputter deposition

The surfactant effect of Ag on the thin film structure of TiO₂ by radio frequency magnetron sputtering has been investigated. Comparisons between the atomic force microscopy images revealed that the surface roughness of TiO₂ film mediated by Ag was smaller than that of the TiO₂ film without Ag. The surface segregation effect of Ag was confirmed using X-ray photoelectron spectroscopy. The results of X-ray diffraction revealed that the initial deposition of a 0.4 nm thick Ag surfactant layer onto a Fe buffer layer prior to the deposition of the TiO₂ film reduced the rutile (110) growth and enhanced the anatase (100) growth. It was concluded that Ag was an effective surfactant for changing the thin film structure of TiO₂ on the Fe buffer layer. The photocatalytic effect of the fabricated TiO₂ film was also investigated using the remote oxidation process. TiO₂ films with the Ag surfactant exhibited higher photocatalytic activity than conventionally deposited TiO₂ films.     

Ag surfactant effects of TiO2 films prepared by sputter deposition

The surfactant effect of Ag on the thin film structure of TiO₂ by radio frequency magnetron sputtering has been investigated. Comparisons between the atomic force microscopy images revealed that the surface roughness of TiO₂ film mediated by Ag was smaller than that of the TiO₂ film without Ag. The surface segregation effect of Ag was confirmed using X-ray photoelectron spectroscopy. The results of X-ray diffraction revealed that the initial deposition of a 0.4 nm thick Ag surfactant layer onto a Fe buffer layer prior to the deposition of the TiO₂ film reduced the rutile (110) growth and enhanced the anatase (100) growth. It was concluded that Ag was an effective surfactant for changing the thin film structure of TiO₂ on the Fe buffer layer. The photocatalytic effect of the fabricated TiO₂ film was also investigated using the remote oxidation process. TiO₂ films with the Ag surfactant exhibited higher photocatalytic activity than conventionally deposited TiO₂ films.     

Conductivity of nanometer TiO2 thin films by magnetron sputtering

The conductivity of nanometer TiO₂ thin films was presented in this paper. The dependence of the conductivity of TiO₂ thin films on the thickness of the film and the substrate material were educed. The TiO₂ films were deposited by reactive magnetron sputtering of a Ti targets in an Ar+O₂ mixture in a conventional sputtering reactor. The thickness of the films deposited on Ti varied in the range from 15 to 225 nm. The resistivity of the films was measured at room temperature in the air. It was found that the conductivity of TiO₂ thin films varies in the range from conductor, semiconductor to nonconductor. This was attributed to electrons transfer at the interface between the TiO₂ and substrates, and the depth of electrons transfer was determined by the difference of work function.     

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.     

Visible light photocatalytic degradation of paraoxon and parathion pesticides on carbon-doped TiO<Subscript>2</Subscript> nanorod thin films

In the present work the nanostructured carbon-doped TiO₂ thin films with nanorod morphology were deposited on glass substrate by a combination of ultrasonic and chemical vapor deposition methods, and for the first time were applied for the photocatalytic degradation of paraoxon and parathion organophosphorus pesticides under visible light irradiation. X-ray Diffraction, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy techniques were used for characterization of the prepared thin films. Obtained results show that presence of carbon element and also special nanorod morphology of the thin films remarkably improve the optical properties of TiO₂ in visible light region and results in the good visible light photocatalytic activity of the thin films for degradation of the pesticides. The photonic efficiencies of the prepared thin films were also examined based on the international ISO-10678:2010 standard protocol for photocatalytic degradation of methylene blue under UV light irradiation. The results show a maximum photonic efficiency of 0.0312% for the carbon-doped TiO₂ thin film with 570 nm thickness, which compared to a reference standard TiO₂ films indicates a 30% improvement in photonic efficiency.     

Preparation, characterization and photocatalytic activity of in situ Fe-doped TiO2 thin films

Fe-doped TiO₂ thin films were prepared in situ on stainless steel substrates by liquid phase deposition, followed by calcination at various temperatures. It was found that some Fe³⁺ ions were in situ doped into the TiO₂ thin films. At 400 °C, the film became photoactive due to the formation of anatase phase. At 500 °C, the film showed the highest photocatalytic activity due to an optimal Fe³⁺ ion concentration in the film. At 900 °C, the photocatalytic activity of the films decreased significantly due to the further increase of Fe³⁺ ion concentration, the formation of rutile phase and the sintering and growth of TiO₂ crystallites.     

2D spinodal phase-separated TiO2 films prepared by sol-gel process and photocatalytic activity

For the purpose of obtaining oxide thin films with high photocatalytic activity, we have successfully prepared the TiO₂ anatase polycrystalline films with a two-dimensional spinodal phase-separated structure (2D-SPSS) in micron size by the sol-gel dip-coating method from a titanium tetraisopropoxide solution containing polyoxyethylene(20) nonylphenyl ether. It has been also found that TiO₂ films with a variety of morphologies in addition to the 2D-SPSS can be formed by controlling the molar ratio of water to titanium tetraisopropoxide. The methylene blue photodegradation activity of the 2D-SPSS TiO₂ film was higher than that of dense TiO₂ film prepared from a TiO₂ sol without co-existing polymer. This fact can be interpreted in terms of possessing a high specific surface area available for the photocatalytic reaction.     

Atomic layer deposition of TiO2 thin films on glass fibers for enhanced photocatalytic activity

Photocatalytic wastewater treatment is expected to become a sustainable way of eliminating toxic chemicals. Due to the surface-driven mechanism of the photocatalysis, surface area of the catalyst material plays a crucial role in the efficiency of the process, which is usually achieved by nanoparticles. However, using powder materials introduces a new problem: removing the catalyst materials out of clean water. As an alternative, atomic layer deposition (ALD) can form conformal thin films on high surface area substrates providing an immobilization route with high photocatalytic activity. Textile materials are inexpensive and accessible therefore good candidates for the substrate materials. Here, we deposit thin films on TiO₂ on fiberglass fabrics and investigate the photocatalytic activity. Since the as-deposited ALD TiO₂ films are amorphous, they have very limited photocatalytic activity. Upon thermal treatment of the films after deposition, photocatalytic activity is achieved. After four hours of exposure to the solar simulator and UV lamp, TiO₂-coated fibers demonstrated much higher photocatalytic activity than films on planar substrates previously described in the literature. The photocatalytic activity and structure of the coated fibers were investigated using XRD, XPS, UV–Vis, and PL analyses.

     

Fabricating highly active mixed phase TiO2 photocatalysts by reactive DC magnetron sputter deposition

Recent work points out the importance of the solid-solid interface in explaining the high photoactivity of mixed phase TiO₂ catalysts. The goal of this research is to probe the structural and functional relationships of the solid-solid interface created by the reactive DC magnetron sputtering of titanium dioxide. We show that sputter deposition provides excellent control of the phase and interface formation. We explored the effects of the process parameters of pressure, oxygen partial pressure, target power, substrate bias (RF), deposition incidence angle, and post annealing treatment on the structural and functional characteristics of the catalysts. We have successfully made pure and mixed phase TiO₂ films. These films were characterized with AFM, SEM, TEM, and XRD to determine surface morphology, phase distribution and phase content. The performance as photocatalytic surfaces was measured and compared (normalized for surface area) to mixed phase TiO₂ fabricated by other methods, including flame hydrolysis powders, and sol-gel deposited TiO₂ films. The sputtered mixed phase materials were far superior to the commercial standard (Degussa P25) and sol-gel TiO₂ as measured by the gas phase oxidation of the air pollutant acetaldehyde under UV illumination. These results demonstrate that reactive DC magnetron sputtering is a powerful tool for investigating the role of the solid-solid interface in influencing photocatalytic activity. In addition, our work illustrates the feasibility of reactive DC magnetron sputtering as a practical commercial technique for manufacturing highly active nanostructured TiO₂ photocatalysts.