Electrochromic properties of sputtered TiO2 thin films

TiO₂ thin films were deposited on ITO/Glass substrates by the rf magnetron sputtering in this study. The electrochromic properties of TiO₂ films were investigated using cyclic voltammograms (CV), which were carried out on TiO₂ films immersed in an electrolyte of 1 M LiClO₄ in propylene carbonate (PC). As- deposited TiO₂ thin film was amorphous, while the films post-annealed at 300~600°C contained crystallized anatase and rutile. With the increase of the annealing temperature, the surface roughness of film increased from 1.232 nm to 1.950 nm. Experimental results reveal that the processing parameters of TiO₂ thin films will influence the electrochromic properties such as transmittance, ion-storage capacity, inserted charge, optical density change, coloration efficiency and insertion coefficient.     

Effect of calcination temperature on the microstructure of porous TiO<Subscript>2</Subscript> film

To obtain porous TiO₂ film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO₂ film was fabricated by the dip-coating technique on glass substrates using this solution. The TiO₂ film was calcined at 500 °C. The maximum thickness of the film from one-run dip-coating was ca. 740 nm. The film was composed of nanosized particle and pores. The porosity of the TiO₂ film was increased by addition of trehalose dihydrate to the sol. The porous TiO₂ films were calcined at different temperatures. The effects of calcination temperature on the microstructure of the porous TiO₂ film were investigated. The porous film prepared from sol containing trehalose still kept the porous structure after calcination at 950 °C. The phase transition temperature of the film from anatase to rutile was shifted from 650 to 700 °C by addition of trehalose to the sol.     

Enhanced Photoactivity in Bilayer Films with Buried Rutile–Anatase Heterojunctions

Herein, we study the photoactivity of anatase–rutile bilayer thin films consisting of an anatase overlayer of variable thickness from some tenths to some hundred nanometers deposited onto a rutile thin film. As references single anatase layers of equivalent thickness were deposited onto silicon. All the films were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The photoactivity of the samples was assessed by following the evolution with the UV illumination time of both the wetting angle on the thin film surface and the decoloration of a dye in a water solution. While a similar efficiency is found for the first type of experiments irrespective of the anatase thickness, in the second type a maximum in the photoactivity is found for a thickness of the anatase layer of about 130 nm. This enhanced photoactivity in bilayer systems with a buried anatase–rutile heterojunction is related to the formation of different Schottky potential barriers in the anatase layer, depending on its thickness and the substrate (i.e. rutile or SiO₂) where it is deposited.     

Preparation of TiO2 Thin Film Photocatalysts by Dip Coating Using a Highly Viscous Solvent

TiO₂ thin film photocatalysts coated onto soda lime glass were prepared by a dip coating process using a highly viscous solvent. The source of the TiO₂ was tetraisopropyl orthotitanate, and -terpineol was used as the solvent. Two types of thin film preparation procedures based on dip coating (a sol-gel system and thermal decomposition system) were used to prepare the samples. TiO₂ thin films were obtained after calcination at 450°C for 1 hour. The film thickness obtained with a single dipping was proportional to the viscosity of the dip coating solutions. The obtained thin films were transparent with a thickness of 1 m. The crystal form of the obtained photocatalyst films was anatase alone. The thin films were formed with aggregated nano-sized TiO₂ single crystals (7–15 nm). The photocatalytic activity of the TiO₂ thin films, as evaluated by the photooxidation of NO (1 ppm) in dry air, was as high as our previous TiO₂ thin films prepared by the sol-gel method.     

Rectifying Properties of Oxide Semiconductor Heterostack Films at Elevated Temperatures

Heterostack films of p-type NiO and n-type TiO₂ semiconductors were deposited by a method of chemical solution deposition on a glass substrate having a sputtered ITO (In₂O₃ doped with Sn) electrode. Transparent films with total thickness of about 280 nm were obtained by heat treatments at 600°C. NiO reacted with TiO₂ to give a NiTiO₃ thin layer between them. The films exhibited a typical rectifying I-V behavior and this property was maintained at 300°C. The thickness of the NiTiO₃ intermediate layer increase with the heating time at 600°C and leading to a decrease of the current density at low voltage.     

总气压与Ar/O2流量比对直流对向靶磁控溅射TiO2薄膜光催化性能的影响

采用对向靶磁控溅射法在不同气压和Ar/O₂流量比条件下, 以氟化SnO₂ (FTO)导电玻璃为基底制备了多晶TiO₂薄膜. 台阶仪测量结果显示所制备TiO₂薄膜的平均厚度约为200 nm. 随着溅射气压的升高, TiO₂薄膜由锐钛矿与金红石混晶结构转变为纯锐钛矿结构. 分别采用场发射扫描电镜(FESEM)和原子力显微镜(AFM)分析了不同气压和Ar/O₂流量比对TiO₂薄膜表面形貌的影响, 结果显示TiO₂薄膜的表面粗糙度随溅射总气压和Ar/O₂流量比的增加而增大. 以初始浓度为100×10^-6 (体积分数)的异丙醇(IPA)气体为目标物检测所制备TiO₂薄膜的光催化性能, 并分析该气相光催化反应的机理, 在紫外照射条件下异丙醇先氧化为丙酮再被氧化为CO₂.当总溅射气压为2.0 Pa、Ar/O₂流量比为1:1时, 溅射所得TiO₂薄膜具备最优光催化活性并可在IPA降解反应中保持较高的催化活性和稳定性.     

Investigation of photocatalytic and low-emissivity properties of TiO2:F films featuring columnar structure prepared on SnO2:F substrate by sol–gel method

Fluorine-doped TiO₂ thin films featuring columnar structure were prepared on fluorine-doped tin oxide (SnO₂:F) substrate using a sol–gel method. The F doping ratios were varied in the range of 0–8 %. The effect of [F]/[Ti + F] ratio on the structural, morphological, optical, photocatalytic and low-emissivity properties has been investigated in detail. X-ray diffraction studies revealed that all the composited films are mainly composed of anatase TiO₂ and rutile SnO₂ without other phases. The prepared TiO₂:F films possessed the columnar morphology with the single layer thickness ranging from 28 to 31 nm. The best photocatalytic activity was obtained for the films with 4 % F doping ratio which is mainly attributed to the highest crystallization and crystallite size. The transmission and hemispherical emissivity of the composite films could still reach approximately 70 % and 0.20, which match the requirements of the Chinese National Standard (GB/T18915.2-2002), promoting the films for the practical applications.     

Facile preparation of vanadium oxide thin films on sapphire(0001) by sol–gel method

The Ba_0.6Sr_0.4TiO₃ (BST60) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method. The thickness of CeO₂, serving as a buffer layer, was varied from 0 to 75 nm, in order to optimize the dielectric tunable property. X-ray patterns analysis indicates that all the thin films exhibit good crystalline quality with a pure perovskite phase and insertion of the CeO₂ buffer layer does not change the crystal structure of BST60. Dielectric properties of the thin films were investigated as a function of both temperature and direct current electric field. The results show that dielectric constant and loss are modified by insertion of the CeO₂ buffer layer. The BST60 thin films with 25 nm thickness CeO₂ buffer layer have the highest figure of merit, low dielectric loss, and suitable dielectric constant, which render them attractive for the tunable microwave device applications.     

Polyethylene glycol assisted direct deposition of rutile TiO2 nanocrystals on transparent conducting oxide substrate for dye-sensitized solar cell applications

Rutile TiO₂ nanocrystals having rectangular faces were directly deposited on fluorine-doped tin oxide coated glass substrates. Using polyethylene glycol-400 as the surfactant, we succeeded in growing a porous rutile layer having maximum thickness of 4.8 μm and containing nanocrystals with lateral dimensions of at least 30 nm. We observed that polyethylene glycol not only controlled the sizes of the nanocrystals but also enhanced the rate of deposition. The nanocrystals had rutile structure and the film was strongly textured with preferential orientation along {002} direction. The dye adsorption properties of the nanocrystalline films depended on their microscopic surface areas which were determined by the sizes of the nanocrystals. A dye-sensitized solar cell, fabricated with a 4.8 μm thick nanocrystalline rutile thin film photoanode, exhibited a light-to-electricity conversion efficiency of 5.02 % under 1.0 sun illumination. The internal resistance, interface capacitance and electron lifetime of dye sensitized solar cell were estimated by electrochemical impedance spectroscopy and an electron lifetime of 0.19 s was recorded.     

Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

Influence of sputter power on structural and electrical properties of TiO2 films for Al/TiO2/Si gate capacitors

Titanium dioxide (TiO₂) thin films were deposited onto p‐Si substrates held at room temperature by reactive Direct Current (DC) magnetron sputtering at various sputter powers in the range 80–200 W. The as‐deposited TiO₂ films were annealed at a temperature of 1023 K. The post‐annealed films were characterized for crystallographic structure, chemical binding configuration, surface morphology and optical absorption. The electrical and dielectric properties of Al/TiO₂/p‐Si structure were determined from the capacitance–voltage and current–voltage characteristics. X‐ray diffraction studies confirmed that the as‐deposited films were amorphous in nature. After post‐annealing at 1023 K, the films formed at lower powers exhibited anatase phase, where as those deposited at sputter powers > 160 W showed the mixed anatase and rutile phases of TiO₂. The surface morphology of the films varied significantly with the increase of sputter power. The electrical and dielectric properties on the air‐annealed Al/TiO₂/p‐Si structures were studied. The effect of sputter power on the electrical and dielectric characteristics of the structure of Al/TiO₂/p‐Si (metal‐insulator‐semiconductor) was systematically investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and characterization of thin TiO2-films on gold/mica

Flat and highly (111) oriented gold and silver films were prepared by physical vapour deposition (PVD) using optimized deposition parameters. On these films, which were characterized with atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), titanium dioxide films were deposited by electron beam evaporation and dip coating. Dip coating from titanium tetraisopropoxide solutions resulted in films with different morphology and coverage depending on the alkoxide concentration (0.009 mol/L – 0.60 mol/L) and the post-treatment. Scanning electron microscopy (SEM) and AFM revealed that the deposited TiO₂ consists of amorphous, highly porous islands when the applied alkoxide concentration is high (0.05 mol/L – 0.6 mol/L). At higher temperatures these amorphous TiO₂ islands sintered significantly and crystallized to anatase. In contrast, transparent TiO₂ films were obtained from low concentrated alkoxide solutions (< 0.01 mol/L) which covered the whole substrate, similar to electron beam evaporated thin films. Sputter profiles with ion scattering spectroscopy (ISS) indicated that the film thickness is in the range of 2 nm when alkoxide solutions with a concentration of 9 mmol/L are used. The deposition of TiO₂ by electron beam evaporation normally resulted in significantly reduced TiO₂ films, completely oxidized ones were obtained when deposition was performed at elevated oxygen partial pressures (p(O₂) > 2 × 10^–5 mbar).     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明:3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

不同基底对TiO2和SiO2薄膜的光学性能的影响

采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO₂和SiO₂薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明：3种基底中, 单晶硅基底上TiO₂和SiO₂薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO₂薄膜折射率和透光率差异较大;SiO₂薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。     

Influence of transition metal-doped titanium(IV) dioxide on the photodegradation of polyethylene

The effects of adding dispersed powders of various forms of titanium(IV) dioxide on the photodegradation of polyethylene have been examined from the following points of view: effect of crystal form, concentration of pigment, transition metal ion, dopant concentration, calcination temperature of pigment, and pigment coating.The rate of photodegradation of polyethylene is reduced by adding certain grades of TiO₂ such as coated TiO₂ particles or TiO₂ doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO₂ doped with V and especially Mo or W ions. The anatase form of TiO₂ is more photoactive than the rutile form, and the effect of increasing the calcination temperature of the pigment is to reduce photoactivity by boosting the rutile fraction. The concentration dependences of the degradation rates are complex, but can be directly related to the percentage of anatase achieved after calcination. Even the most aggressive of the metal-doped pigments are less photoactive than the Degussa P25 material, containing both rutile and anatase.     

Short time deposition of TiO2 nanoparticles on SiC as photocatalysts for the degradation of organic dyes

The deposition of TiO₂ nanoparticles on SiC was carried out by mechanical milling under different conditions. SiC–TiO₂ samples were used as photocatalysts for the degradation of organic dyes such as methylene blue and rhodamine B. A short time deposition of TiO₂ nanoparticles was observed during mechanical milling (2 min at 200 rpm) to cover the SiC particles. The presence of SiC and TiO₂ (anatase and rutile) was confirmed by means of X-ray diffraction after thermal treatment at 450 °C. The deposition of TiO₂ on SiC was corroborated by scanning electron microscopy analysis; the thickness of the thin layer of TiO₂ deposited on SiC increases as the proportion of TiO₂ increases. The energy band gap values obtained for these compounds were around 3.0 eV. SiC–TiO₂ photocatalysts prepared by mechanical milling exhibited better activity under UV-light irradiation for the degradation of methylene blue and rhodamine B than commercial TiO₂ powder (titania P25).     

Growth mechanism of Nb-doped TiO<Subscript>2</Subscript> sol–gel multilayer films characterized by SEM and focus/defocus TEM

TiO₂ and Nb-doped TiO₂ films were prepared by sol–gel processing, their microstructure was adjusted by varying the number of subsequent coating-firing cycles that resulted in final total film thickness of ~100 nm. When only few subsequent coatings are stacked (large single layer thickness) granular polycrystalline microstructures are observed. Doping with Nb reduces the crystallite size compared to the respective pure anatase films. When the single layer thickness is reduced, the film growth is successively dominated by the nucleation of subsequent films on the underlying crystalline material resulting in a columnar dense film structure. The multilayer architecture of such films can be demonstrated by defocus TEM imaging even if crystalline columns exceed single film boundaries. Results indicate that Nb is homogeneously incorporated into the anatase lattice by substitution of Ti, nevertheless the electric conductivity after H₂ post annealing is significantly lower than reported for analogous films prepared by magneton sputtering or pulsed laser deposition.     

Preparation of TiO<Subscript>2</Subscript> nanofibers immobilized on quartz substrate by electrospinning for photocatalytic degradation of ranitidine

The photocatalytic activity of TiO₂ nanofibers immobilized on quartz substrates was investigated by evaluating the decomposition of organic pollutants. TiO₂ nanofibers were synthesized by electrospinning the Ti-precursor/polymer mixture solution, followed by hot-pressing for enhancing the adhesion of TiO₂-nanofiber films to the substrates. TiO₂ started to crystalize in the anatase form at 500 °C and reached the optimal photocatalytic anatase/rutile phase ratio of 70:30 at a calcination temperature of 600 °C. The TiO₂-nanofiber film was demonstrated to be an efficient photocatalyst by ranitidine decomposition under UV illumination and was proven to have a comparable photocatalytic activity with the well-known Degussa P25 nanoparticulate photocatalyst and excellent recyclability during 10 cycles of photocatalytic operation, indicating no loss of TiO₂ nanofibers during photocatalytic operations.     

Porous “sponge-like” anatase TiO2 via polymer templates: synthesis, characterization, and performance as a light-scattering material

The synthesis of porous “sponge-like” TiO₂ via a polymer gel coating technique is presented. The experimental procedure involves the preparation of a gelled polymerizable microemulsion. The polymerization of the latter leads to porous poly-N-isopropylacrylamide which forms a hydrogel in the presence of water. Via solvent exchange, a suitable TiO₂ precursor is infiltrated into this structure after which its in situ hydrolysis is triggered to form porous amorphous TiO₂. The subsequent calcination step allows the removal of the polymer template and the transformation of amorphous TiO₂ into porous, crystalline anatase with domain sizes ranging from 200 to 250 nm. As a means of verification and proof of concept, this material is tested as light-scattering layer in dye-sensitized solar cells (DSSC), and it is found that the resulting solar cell performance is comparable to commercially available TiO₂. However, an increased tendency to form rutile during DSSC fabrication was noticed when compared to commercial TiO₂. As there is a large potential for optimizing the synthesis, the proposed procedure is a promising route towards porous TiO₂ that performs significantly better as scattering layer in light-harvesting and optical devices.