Anatase Films Research Articles

STRUCTURAL PROPERTIES OF NITROGEN DOPED ANATASE AND RUTILE TiO2 THIN FILMS

Anatase and rutile TiO2 thin films have been doped by N ion implantation. The effect of N doping on the structural changes of TiO2 thin films and its correlation to the optical and chemical properties of the films is investigated. The depth and concentration of the implanted N atoms is found not to exhibit substantial difference for anatase and rutile phases. The energy loss of the implanted N atoms correlates well to the energy gained by O and Ti atoms in the TiO2 lattice. An increased number of O vacancies are found to be generated as compared to Ti for both anatase and rutile phases. The energy loss mechanisms of the implanted N atoms together with the O vacancy generation are found to be the major driving forces for facilitating enhanced optical and chemical properties of the TiO2 thin films.Â

Effect of the nanocrystalline structure type on the optical properties of TiO2:Nd (1 at.%) thin films

Titanium dioxide thin films, each doped with the same amount of neodymium (1at.%) were deposited by Low Pressure Hot Target Reactive Sputtering and High Energy Reactive Magnetron Sputtering processes in order to obtain anatase and rutile thin film structures respectively. The microstructure and phase composition were analyzed using the transmission electron microscopy method including high resolution electron microscopy imaging. The measurements of the optical properties showed, that both prepared thin films were transparent in the visible light range and had a low extinction coefficient of ca. 3⋅10−3. The thin film with the anatase structure had a lower cut-off wavelength and refractive index and a higher value of optical energy band gap as-compared to the TiO2:Nd coating with the rutile structure. Simultaneously, more efficient photoluminescence emission was observed for the rutile thin films.

Titanium Dioxide Thin Films Deposited by Electric Field‐Assisted CVD: Effect on Antimicrobial and Photocatalytic Properties**

Thin films of anatase titanium dioxide are deposited on fluorine‐doped tin oxide (FTO) glass substrates utilizing the electric field‐assisted aerosol (EA)CVD reaction of titanium isopropoxide in toluene at 450 °C. The as‐deposited films are characterized using scanning electron microscopy (SEM), X‐ray diffraction (XRD), Raman spectroscopy (RS), and UV‐vis spectroscopy. The photoactivity and antibacterial activity of the films are also assessed. The characterization analysis reveals that the use of an electric field affects the film microstructure, its preferential orientation, and the functional properties. XRD of the anatase films reveals that the application of electric fields causes a change in the preferential orientation of the films from (101) to (004) or (211) planes, depending on the strength of the applied field during the deposition.

A one-pot synthesis of nanostructured mesoporous TiO2 films on graphite felt substrates for fast catalysis

Crack-free mesoporous anatase films are obtained on graphite felt using a one-pot synthesis from a precursor solution. The films are characterized by high photocatalytic performance in comparison to macro-mesoporous films on silicon substrates.

Deposition of porous titanium oxide thin films as anode material for dye sensitized solar cells

Crystallized nanoporous TiO2 thin films were synthesized by combining reactive magnetron sputtering and Glancing Angle Deposition (GLAD). The growth temperature, the bias voltage and the rotation speed of the substrate were studied with the aim to grow nanoporous films presenting anatase constitution which are suitable for Dye Sensitive Solar Cells (DSSC) applications.By fixing the tilt angle at 85°, we have shown that an increase of the growth temperature up to 450 °C leads to the formation of nanoporous anatase film with a grain size up to 24 nm while by applying a bias voltage leads to a densification of the films as evidenced by scanning electron microscopy and by X-ray diffraction. On the other hand, by rotating the substrate (from 0.1 to 10°/s) during the deposition process, films with larger columns and higher surface roughness (from 45 to 60 nm) were obtained due to an enhanced shadowing effect.Preliminary dye impregnation experiments have shown that the highest light absorption values are obtained for the films prepared without bias and with no rotation, which is supported by the microstructure of these films presenting the highest porosity. These films, presenting an anatase constitution, are potentially good candidates as an anode in DSSC applications.

TiO2 films prepared using plasma ion assisted deposition for photocatalytic application

Anatase TiO2 films were synthesized on glass substrates using a plasma ion assisted deposition (PIAD) without external heating or subsequent annealing. The low temperature PIAD process produced crystalline anatase films with increased hardness and Young’s modulus, reduced film surface roughness and improved optical properties compared with those deposited without ion assistance, as well as a possibility to be applied to a wider range of substrates. Photocatalytic characterization showed that significant increases in photocatalytic stability and efficiency were achieved after using the PIAD process, although surface roughness and porosity of the films decreased slightly.

Tuning the Photocatalytic Activity of Anatase TiO2 Thin Films by Modifying the Preferred <001> Grain Orientation with Reactive DC Magnetron Sputtering

Anatase TiO2 thin films were deposited by DC reactive magnetron sputtering on glass substrates at 20 mTorr pressure in a flow of an Ar and O2 gas mixture. The O2 partial pressure (PO2) was varied from 0.65 mTorr to 1.3 mTorr to obtain two sets of films with different stoichiometry. The structure and morphology of the films were characterized by secondary electron microscopy, atomic force microscopy, and grazing-angle X-ray diffraction complemented by Rietveld refinement. The as-deposited films were amorphous. Post-annealing in air for 1 h at 500 °C resulted in polycrystalline anatase film structures with mean grain size of 24.2 nm (PO2 = 0.65 mTorr) and 22.1 nm (PO2 = 1.3 mTorr), respectively. The films sputtered at higher O2 pressure showed a preferential orientation in the <001> direction, which was associated with particle surfaces exposing highly reactive {001} facets. Films sputtered at lower O2 pressure exhibited no, or very little, preferential grain orientation, and were associated with random distribution of particles exposing mainly the thermodynamically favorable {101} surfaces. Photocatalytic degradation measurements using methylene blue dye showed that <001> oriented films exhibited approximately 30% higher reactivity. The measured intensity dependence of the degradation rate revealed that the UV-independent rate constant was 64% higher for the <001> oriented film compared to randomly oriented films. The reaction order was also found to be higher for <001> films compared to randomly oriented films, suggesting that the <001> oriented film exposes more reactive surface sites.

Chemically grown TiO2 on glass with superior photocatalytic properties

TiO2 anatase and Degussa (Enovik) P25 thin films were deposited on glass using the sol–gel technique at 600 and 80°C, respectively. The structural, morphological and optical properties of the as-grown TiO2 films were studied against their thickness, for both of the experimental procedures described. Moreover, the photocatalytic activity of the TiO2 samples was investigated regarding the degradation of stearic acid and the decolorization of methylene blue, under UV-A light illumination. In specific, the 90nm-thick (4×) Degussa P25 TiO2 films deposited on glass at 80°C is by far the more photocatalytically active against methylene blue decolorization, reaching an apparent rate constant of 0.094min−1, while the photocatalytic activity of the 110nm-thick (4×) TiO2 thin films deposited on glass at 600°C by sol–gel show the highest stearic acid disappearance rate, i.e., 9.46×10−8mol/min (formal quantum efficiency=10.02×10−3) at 15min of UV-A light illumination.

Electronic and optical properties of TiO2 and its polymorphs by Z-scan method

TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable properties. TiO2 is known to exist in nature in three different crystalline structures: rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol—gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of χ(3) for amorphous, anatase, and rutile are also calculated and found to be 5 × 10−19 m2/V2, 27 × 10−19 m2/V2, 19 × 10−19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.

Photocatalytic activity of anatase and rutile TiO2 epitaxial thin film grown by pulsed laser deposition

Epitaxial rutile-TiO2(011) and anatase-TiO2(001) films have been grown by pulsed laser deposition on Al2O3(1¯102) and LaAlO3(100), respectively. For low growth rates of ~0.0012nm/s and growth temperatures of 600°C high quality films are obtained. In particular the anatase films exhibit 100nm wide flat terraces for 10–15nm film thickness. Atomic steps of both ~0.25 and ~0.5nm are measured, suggesting the existence of two different terminations, although only a 4×1 reconstruction is observed in reflection high-energy electron diffraction. The rutile films exhibit coherent twin domain boundaries, which is likely the reason for smaller terrace sizes compared to anatase films. Photocatalytic activity of the films is measured by decomposition of methyl orange solution under UV-irradiation. The anatase films are about twice as active as the rutile films. For both films the activity does not change significantly for films of 10nm and thicker. For rutile films the activity is also compared to that of single crystal rutile TiO2(011) samples. Both rutile-films and single crystals exhibit very similar activity, indicating the good quality of the films. Post-growth annealing of the films in air at 600°C decreases the photocatalytic activity of the films. On the other hand, reduction of thin films by vacuum annealing to 800°C does not change the photocatalytic activity of the films significantly compared to the as grown films. This is in contrast to single crystal rutile samples whose photocatalytic activity for the decomposition of methyl orange almost doubles after reduction by high-temperature annealing in vacuum compared to the stoichiometric bulk-samples. The differences between films and bulk samples may hint differences in defect formation due to the substrate interface.

Sol–gel derived Ag-containing TiO2 films on surface roughened biomedical NiTi alloy

Ag-containing TiO2 films (Ag/Ti=3.3, 9.1 at%) were sol–gel coated on NiTi alloy that had been surface roughened by the NaOH–HCl treatment for antibacterial application. Thermal analyses of the dried gels reveal that the addition of 9.1 at% Ag lowers the anatase-rutile transformation temperature from 618 to 586°C. Morphological observation shows that surface roughening and silver addition improve structural integrity of the TiO2 films. X-ray diffraction reveals that the addition of Ag does not obviously change crystallinity of the anatase films. X-ray photoelectron spectroscopy results indicate metallic nature of Ag in the film and complete coverage of the films on the roughened alloy substrate. Microindentation test exhibits that the Ag–TiO2 film on the roughened substrate has higher cohesive strength than that on the polished substrate. The potentiodynamic polarization test in a Ca-free Hank׳s balanced salt solution demonstrates good protection of the TiO2 and Ag–TiO2 films for the alloy substrate. Ultraviolet light illumination for 3h can increase surface hydrophilicity of the coated NiTi samples by reducing contact angles from >65° to <20°.

Preparation and mechanism of TiO2-coated illite composite pigments

TiO2-coated illite composite pigments were prepared by hydrolyzing Ti(SO4)2 on the surface of illite substrates and the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), zeta potential analysis, and X-ray photoelectron spectroscopy (XPS), respectively. Density functional theory calculations of the energetic stability and electronic structure of illite, calcined illite, and TiO2-coated illite were used to analyze the chemical activity and bonding position between the anatase film and the illite particles. The results demonstrate that calcined illite is more suitable for metatitanic acid coating. Moreover, the surface of illite substrates is continuously coated with anatase and a chemical interaction could occur between the anatase film and the illite substrates. The whiteness, hiding power, and oil absorption value of the compound pigment are 95.73%, 97.55%, and 33.82 g/100 g, respectively.

Anatase and rutile TiO2 thin films prepared by reactive DC sputtering at high deposition rates on glass and flexible polyimide substrates

Titanium oxide thin films have been prepared by reactive DC sputtering at room temperature on soda-lime glass (SLG) and flexible polyimide (Kapton) substrates. The sputtering conditions have been adjusted in order to achieve high deposition rates between 15 and 45 nm/min. Post-deposition heating of the samples has been performed at 350 °C in nitrogen during 30 min. The crystalline structure of these films and their optical, morphological, and electric characteristics have been studied before and after annealing by X-ray diffraction, spectrophotometric measurements, atomic force microscopy, and the four-point probe method. The optical data indicate that pure anatase phase, which crystallizes after the heating process, is obtained on both SLG and Kapton substrates at the lowest deposition rate (15 nm/min). In this case, the samples exhibit high electric resistivity above 300 Ωcm. Otherwise, for the highest deposition rate (45 nm/min), crystalline rutile is identified in the as-grown and heated films, with a lower optical gap energy than anatase and also a lower resistivity that reaches 0.3 Ωcm after heating. At intermediate deposition rates, anatase and rutile coexist in the samples as has been verified by X-ray diffraction, although the overall optical and electric characteristics are dominated by the rutile phase. Analogous titanium oxide layers have been obtained on SLG and Kapton, and this opens the possibility of substituting flexible plastics for conventional glass substrates.

Nanocrystalline Rutile Electron Extraction Layer Enables Low-Temperature Solution Processed Perovskite Photovoltaics with 13.7% Efficiency

We demonstrate low-temperature (70 °C) solution processing of TiO2/CH3NH3PbI3 based solar cells, resulting in impressive power conversion efficiency (PCE) of 13.7%. Along with the high efficiency, a strikingly high open circuit potential (VOC) of 1110 mV was realized using this low-temperature chemical bath deposition approach. To the best of our knowledge, this is so far the highest VOC value for solution-processed TiO2/CH3NH3PbI3 solar cells. We deposited a nanocrystalline TiO2 (rutile) hole-blocking layer on a fluorine-doped tin oxide (FTO) conducting glass substrate via hydrolysis of TiCl4 at 70 °C, forming the electron selective contact with the photoactive CH3NH3PbI3 film. We find that the nanocrystalline rutile TiO2 achieves a much better performance than a planar TiO2 (anatase) film prepared by high-temperature spin coating of TiCl4, which produces a much lower PCE of 3.7%. We attribute this to the formation of an intimate junction of large interfacial area between the nanocrystalline rutile TiO2 and the CH3NH3PbI3 layer, which is much more effective in extracting photogenerated electrons than the planar anatase film. Since the complete fabrication of the solar cell is carried out below 100 °C, this method can be easily extended to plastic substrates.

Ordered Macro‐/Mesoporous Anatase Films with High Thermal Stability and Crystallinity for Photoelectrocatalytic Water‐Splitting

Hierarchically ordered macro-/mesoporous TiO2 films with a large surface area, huge pore volume, highly crystalline framework, and continuous morphology are successfully synthesized using a confined evaporation-induced self-assembly (EISA) method accompanied by a surfactant sulfuric acid carbonization method. The films exhibit excellent photoelectrocatalytic water-splitting performance. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Thermally induced structural modifications of nano-sized anatase films and the effects on the dye-TiO2 surface interactions

Nano-sized TiO2 films have been grown by DC-Reactive Sputtering at ∼150°C on [0001] ZnO:Al substrates to be applied in Dye Sensitized Solar Cells. The effects of post-deposition thermal treatment at 500°C on the optical and structural (density, grain size) properties of the TiO2/ZnO:Al bi-layers have been investigated in details. The effects of such modifications on the surface properties, have been evaluated by dye-sensitization with 5,10,15,20 Tetrakis(4-carboxyphenyl) porphyrin (TCPP). Different interactions of the probe-molecules with the as grown and annealed TiO2 surfaces have been observed. In particular, Quantum yield (QY) analysis of TCPP-sensitized films showed that the emitted/absorbed photons ratio in the as grown layers is a factor of ∼3 lower than in the annealed layers. Based on simplified test solar cells, the electron injection is thought to be the most appropriate mechanism to explain the QY results. Our approach gives particular emphasis to the role of the surfaces and the interfaces involved in the TCPP/TiO2/AZO multilayer structures with the intent of proposing the as sputtered TiO2 layer as blocking layer in complete architecture for low thermal budget solutions (<200°C).

PbO-Modified TiO2 Thin Films: A Route to Visible Light Photocatalysts

PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface.

Searching for the formation of TiO2 mesoporous films with durable photoactivity by synergy of WO3 and sodium using a simple sputtering and annealing process

The fabrication of anatase TiO2 thin films with a mesoporous framework by template-directing sol–gel or microemulsion method has drawn considerable attention because of the compound's highly photocatalytic and superhydrophilic properties and its potential use in a wide variety of applications, such as self-cleaning and anti-fogging. In this study, thin films of TiO2, coupled with a widely ranging amount of WO3, are sputter deposited onto soda-lime glass, and the segregation of WO3 by annealing, along with the alternation of their microstructures and underlying reaction mechanisms involving sodium, is examined. This research highlights a sputtering process to synthesize mesoporous anatase films with a refined, regular grain structure and controlled porosities, via the synergy of WO3 and sodium to form a water-soluble sodium tungstate through a simple annealing process. In contrast to what is generally agreed that sodium contaminates TiO2 photocatalysts, the films impacted by sodium exhibit exceptional durability and much better photoactivity than the undoped anatase films at degrading a hydrocarbon layer and giving a long-last super-wetting surface. The enhancement of the films’ photocatalytic activity is elucidated by structural analysis and porosity identification.

Fabrication of a TiO2 photocatalyst by anodic oxidation of Ti in an acetic acid electrolyte

We anodized Ti substrates in an aqueous acetic acid solution to produce photocatalytic TiO2 films. The TiO2 films were comprised of the anatase phase, but the crystallinity and photocatalytic activity were low, in contrast to films produced by Ti anodization in a sulfuric acid electrolyte. After annealing, the anatase film crystallized and the photocatalytic activity was greatly enhanced. For the anodizations carried out in 0.5 and 2M acetic acid, nonzero current was maintained for the duration of anodization, unlike the other concentrations. We interpret this phenomenon as the layered structure formation from the holes on the substrate surface. Highly crystallized anatase TiO2 therein was thought to mainly contribute to photocatalysis.

Mesoporous and mesostructured TiO2 coatings for photocatalytic applications

The correlation between the textural properties and the photocatalytic activity of nanocrystalline Titanium dioxide (TiO2)-anatase films obtained by sol–gel has been investigated. Mesoporous and mesostructured TiO2-anatase films were prepared using different titanium precursors and Pluronic (F127) and polyethylene glycol hexadecyl ether P5884 (Brij58) surfactants via acid catalysis. Ca(NO3)2 and WCl6 were incorporated to TiO2 sols to investigate the effect of the doping on the photocatalytic behaviour. The microstructure and textural properties were characterised by X-ray diffraction, spectral ellipsometry and transmission electronic microscopy. The photocatalytic properties were evaluated in aqueous solution (methyl orange) and in gas phase (trichloroethylene, sulphide acid and methyl-ethyl-ketone) using multilayer films deposited on glass-slides. TiO2-B-Brij-58 films exhibited the most efficient photocatalytic activity either in aqueous or gas medium. The Ca doping strongly enhances the photocatalytic activity associated with the reduced recombination of electrons and holes in the catalyst.