TiO2 photoanodes prepared by cathodic electrophoretic deposition in 2-propanol: effect of the electric field and deposition time

This paper evaluates the influence of electric field and deposition time applied on cathodic electrophoretic formation of TiO₂ films in organic medium (2-propanol). The film morphology was tracked by measuring the deposited mass and film thickness. The variation in film porosity was correlated with the apparition of surface states distribution in the cyclic voltammetric characterization in the dark, due to grain boundaries defects generated in the contact of the TiO₂ particles. The open-circuit voltage decay curves showed that there is no formation of deep energy states inside the band gap of the TiO₂. The photopotential of the films increased until a critical thickness but the photocurrents showed to be dependent on operational variables, due to the fact that anodic polarization in thin films increases the electric field generated by the illumination at the ITO/TiO₂ interface, favoring the transport of the photogenerated electrons to the rear contact.     

Atomic layer deposition of TiO2−xNx thin films for photocatalytic applications

Titanium dioxide (TiO₂) is recognized as the most efficient photocatalytic material, but due to its large band gap energy it can only be excited by UV irradiation. Doping TiO₂ with nitrogen is a promising modification method for the utilization of visible light in photocatalysis. In this work, nitrogen-doped TiO₂ films were grown by atomic layer deposition (ALD) using TiCl₄, NH₃ and water as precursors. All growth experiments were done at 500 °C. The films were characterized by XRD, XPS, SEM and UV–vis spectrometry. The influence of nitrogen doping on the photocatalytic activity of the films in the UV and visible light was evaluated by the degradation of a thin layer of stearic acid and by linear sweep voltammetry. Light-induced superhydrophilicity of the films was also studied. It was found that the films could be excited by visible light, but they also suffered from increased recombination.     

Thick transparent rutile TiO2 films crystallized in solution

We report a novel process for the preparation of dense, transparent TiO2 films of 2.5 mum thickness on a F-doped SnO2-covered glass substrate. The starting solution contained peroxotitanate complex ions, which are relatively stable under the experimental conditions, permitting the deposition of highly textured rutile nanocrystalline films. The nanocrystals exhibit specific orientations along the (101) and (002) crystalline planes. Kinetic studies suggest that the precipitation started from the formation of amorphous solids, followed by crystallization through a dissolution-recrystallization process. Although a minor phase of anatase was detected only for powders collected from solutions after film preparation, not for films, the transformation from amorphous to anatase was believed to occur before further transformation of anatase to rutile. The present method enables film synthesis on a surface with a large area, and therefore could be integrated into the processing of electroluminescent devices.     

A novel reaction model for the electrical conductivity of ultra-thin TiO2 films in H2

Two ultra-thin TiO(2) films with platinum electrodes were prepared on a porous anodic aluminium oxide thick layer and a ceramic plate, respectively. It was found that in both TiO(2) films the conductance was almost proportional to the fourth root of the H(2) concentration in N(2) ambient at 500 °C. A quantitative model based on the spill-over mechanism is established to describe this novel correlation.     

抗体固载于TiO2多孔膜的压电免疫型细菌传感器

在镀银的压电石英晶体上沉积一层TiO2纳米粒多孔膜,用3 氨丙基三乙氧基甲硅烷将其活化后,借助于戊二醛实现了特异性抗体(抗肠道沙门氏菌抗体)在压电石英晶体上的有效固载,并用于肠道沙门氏菌的快速检测。其检测下限为4×104cells mL,检测时间为30min。可用于价格低廉的镀银石英晶体,有望成为开发一次性压电型免疫检测探头的有效方法。     

TiO2 films by sol-gel spin-coating deposition with microbial antiadhesion properties

Intensive use of antibiotics induced adaptations in bacteria, which developed antibiotic resistance. This is becoming a serious health problem, particularly in the hospital, food industry, or public transport. It is also important to produce surfaces that not only are bactericidal but also prevent adhesion and the consequent biofilm formation, which can make the bacteria resistant to conventional disinfection methods. In this work, a simple and inexpensive method to obtain surfaces TiO₂ film coated has been realized to prevent attachment and bacterial proliferation on surfaces. The synthesis and deposition procedure has been finalized to the realization of a uniform coating, whose physical, morphological, and structural features are suitable to inhibit the proliferation of the bacteria and in particular the adhesion of the biofilm. The suitability of the obtained coating has been attested by RBS, X-ray diffraction (XRD), SEM, UV-vis, and Raman techniques. The obtained coatings were homogeneous anatase titania films with an excellent adherence to the substrate and a transmittivity higher than 80% in the visible region. The results show that the TiO₂ films considerably reduce microbial contamination on the surface (~98% reduction) feature that makes this coating suitable for antibacterial applications.     

Spectroscopic ellipsometry investigations of porous SiO2 films prepared by glancing angle deposition

We present the optical and the structural properties of porous SiO₂ films fabricated by using a glancing angle deposition technique. The influence of the glancing angle on the pseudorefractive index of porous SiO₂ films was studied by spectroscopic ellipsometry in the UV–visible region. The relationships among the pseudorefractive index, the porosity, and the glancing angle are determined. The results show that the pseudorefractive index decreases and the porosity increases with the increase of glancing angle. The minimum pseudorefractive index is found to be 1.11 at 532 nm for the porous SiO₂ film deposited at a glancing angle of 87°. The structural and surface morphology of these samples was also investigated by using a scanning electron microscope. The results indicate that the as‐deposited SiO₂ thin films are porous with a tilted‐columnar structure and low pseudorefractive index. Copyright © 2013 John Wiley & Sons, Ltd.     

Anatase TiO2 porous thin films prepared by sol-gel method using CTAB surfactant

Anatase TiO₂ porous thin films were prepared on glass substrates by sol-gel method with Cetyltrimethylammonium Bromide (CTAB) as a pore-forming agent, Tetrabutylorthotitanate as Ti precursor, ethanol as solvent and diethanolamine as chelating agent respectively. IR, TG-DSC, XRD and SEM analyzed the chemical and physical changes during sol-gel process and characteristics of the films. Effects of the amount of CTAB, alkane and water on morphology of the films were discussed and the principle of forming porous structure was proposed. It was shown that the diameter of pores was changed in the range of 30–400 nm.     

Internal structure of nanoporous TiO2/polyion thin films prepared by layer-by-layer deposition

The internal structure of porous TiO2 films prepared by electrostatic layer-by-layer deposition was investigated. The films were prepared by alternate dipping of solid substrates into dispersions of TiO2 nanoparticles and polycations, polyanions, or pure buffer solution, respectively. The surface charge of the amphoteric TiO2 particles was controlled by the pH of the aqueous dispersions. The morphology of the film surface was investigated by means of scanning electron microscopy. It was found that the surface roughness strongly depends on the polymeric material used for the deposition process but is independent of the ionic strength of the solution or the molecular weight of the polyions. The samples with rough surfaces feature strong light scattering. The porosity and internal structure of the TiO2/polyelectrolyte films were investigated by adsorption/desorption of dye molecules. A crude estimate yields an internal surface that is up to 160 times the plane surface of the substrate for a film thickness of 1 microm. The composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). Detection of the XPS signal after each deposition step of the first three dipping cycles shows a significant increase of the relative surface coverage of Ti after the TiO2 deposition step and of PSS after the PSS deposition step. For later dipping cycles, such an increase was also detectable but less prominent.     

Efficient electrochromic performance of anatase TiO2 thin films prepared by nebulized spray deposition method

Anatase TiO₂ thin films with high optical modulation, better reversibility, fast switching time, and enhanced coloration efficiency were prepared by nebulized spray pyrolysis technique. X-ray diffraction study confirmed the formation of anatase phase TiO₂ in the present work. This inference was substantiated from the Raman active modes of A_1g, 2 B_1g, and 3 E_g corresponding to O–Ti–O bond in TiO₂. The PL emission peak observed at 400 nm is corresponds to the indirect transition (X_1b?→?Γ₃) from the conduction band to the valence band. The average reflectance of TiO₂ thin films was varied from 31 to 20%. The electrochemical study revealed the excellent performance of TiO₂ films with high optical modulation (ΔT?=?61%), fast switching kinetics (t _b ?=?1.6 s, t _c ?=?2.4 s), good coloration efficiency (100 cm² C^?1), and better reversibility (86%). The efficient electrochromic behavior of films may be due to the smooth microstructure nature, which provides an easy pathway for the diffusion and charge transfer process of Li⁺ ions in TiO₂ film matrix. The fast transfer of Li⁺ ion was realized from the electrochemical impedance spectroscopic measurement.     

Aluminum hydroxocarboxylates in solution deposition of planarization alumina films

Aluminum hydroxocarboxylates derived from butyric, pivalic, valeric, and isovaleric acids were synthesized and characterized. The synthesized hydroxocarboxylates were suspended in isopropanol and reacted with diethylenetriamine and monoethanolamine, which acted as hydrolyzing and complex-forming agents, to obtain precursor solutions for chemical deposition of smooth amorphous alumina films on metal substrates.     

Study of the crystallization pathway of Na0.5Bi0.5TiO3 thin films obtained by chemical solution deposition

Na_0.5Bi_0.5TiO₃ (NBT) thin films were fabricated by a chemical solution deposition (CSD) method. A route involving the reaction between sodium and bismuth acetates and titanium n-butoxide was used to synthesise the different precursor solutions. The thermal decomposition and crystallization pathways of different modified precursors have been studied by thermal analysis and X-ray diffraction techniques. As a consequence of the modification of the precursor solutions and their different thermal behaviour, the nucleation of the stable perovskite phase happens at different temperatures depending on each case but is found to be at temperatures as low as 500 °C. For the thin film processing, the drying and pyrolysis temperatures were chosen according to the thermogravimetric data to minimize the strain resulting from the shrinkage of the film during the elimination of solvents and organic ligands. The crystallization process was studied and the experimental results are discussed in terms of structural, microstructural and electrical features investigated by field-emission scanning electron microscopy, atomic force microscopy in tapping and piezo-force modes and X-ray diffraction.     

Light-excited superhydrophilicity of amorphous TiO2 thin films deposited in an aqueous peroxotitanate solution

We report on the photoinduced superhydrophilicity of the surface of amorphous TiO2. Amorphous TiO2 thin films were prepared on self-assembled monolayers by the peroxotitanate-complex deposition (PCD) and liquid-phase deposition (LPD) methods. The surface morphology and topography were characterized in detail. The contact angles were 34 degrees and 66 degrees for the as-deposited thin films through the PCD and LPD methods, respectively, which slowly increased to about 70 degrees and 73 degrees after being stored in air. After irradiation by UV light, the contact angle vanished and the surface exhibited superhydrophilicity. The superhydrophilicity and hydrophobicity could be switched by alternatively exposing the surface to UV light and drying in an atmosphere filled with organic gases. Although the oxidation of the contamination on the surface has effects on the increase in hydrophilicity, the X-ray photoelectron spectroscopy results suggested that the superhydrophilicity was also related to the transformation of the Ti-OH groups to groups that have dangling bonds. This paper indicates that an amorphous TiO2 thin film does not need to be heated to obtain superhydrophilicity; such a self-cleaning surface can be achieved at room temperature by our newly developed environmentally friendly method.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on IT0 coated glass by pulsed laser ablation of metallic Ti target in 0₃/0₂ ambient gases. The intercalation of Li ions in the anatase TiO₂ film electrode is examined by cyclic voltammetry. The electrochromic behaviour of TiO₂ electrode is investigated byin-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These results suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property. Project supported by the National Natural Science Foundation of China (Grant No. 29783001) and State Key Laboratory for Physical Chemistry of Solid Surface of Xiamen University (1997).     

Synthesis and visible light photocatalytic properties of polyoxometalate-thionine composite films immobilized on porous TiO2 microspheres

Multilayer films (PW(12)-TH)(n) (PW(12)=PW(12)O(40)(3-), TH=thionine) were immobilized on porous anatase TiO(2) microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO(2) was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO(2) template particles had a round shape with an average diameter of 250 nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW(12)-TH)(n) composite films onto TiO(2) microspheres, and the growth of PW(12)-TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW(12)-TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO(2) became weaker when immobilized (PW(12)-TH)(n). The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO(2) and PW(12) showed an excellent photocatalytic performance. Both TH sensitization and PW(12) adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW(12)-TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.     

Preparation and characterization of CuAlO2 transparent thin films prepared by chemical solution deposition method

CuAlO₂ thin films were prepared on quartz glass and sapphire substrates by chemical solution deposition method using copper acetate monohydrate, aluminum nitrate nonahydrate and 2-methoxyethanol as starting precursor and solvent. The effects of annealing temperature on the structural, morphological, electrical and optical properties have been studied. Via the optimized annealing treatment condition, CuAlO₂ film annealed at 850 °C in nitrogen flow of 400sccm under atmosphere pressure exhibits the best performance with the lowest room temperature resistivity of 3.6 × 10² Ω cm and the highest optical transmission in the visible region (>70% at around 600 nm wavelength). CuAl₂O₄ and CuO phases, not CuAlO₂ phase are obtained when annealing temperature is lower than 850 °C. However, a further increase of annealing temperature weakens the crystallization quality and deteriorates the surface morphology of CuAlO₂ films as the annealing temperature exceeds 850 °C, leading to an increase in the resistivity and a decrease of the optical transmission in the visible region of CuAlO₂ films.     

Oriented polymers from solution. I. A novel method for producing polyethylene films

A novel method for the production of uniaxially oriented polyethylene film is demonstrated, it being an extension of the “surface growth” method for obtaining polyethylene fibers from solution using a Couette apparatus. The film growth is found to be affected by temperature, rotor speed, rotor material, and surface roughness. Together with its possible practical importance, film growth is presented as a useful means of sample preparation and as a way to increased linear fiber growth rates. In addition, its use for studies on solution grown polypropylene fibers is indicated as well as its implications for “surface growth” of polymer crystals in general.