Fast fabrication of long TiO2 nanotube array with high photoelectrochemical property on flexible stainless steel

Oriented highly ordered long TiO2 nanotube array films with nanopore structure and high photoelectrochemical property were fabricated on flexible stainless steel substrate (50 microm) by anodization treatment of titanium thin films in a short time. The samples were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and photoelectrochemical methods, respectively. The results showed that Ti films deposited at the condition of 0.7 Pa Ar pressure and 96 W sputtering power at room temperature was uniform and dense with good homogeneity and high crystallinity. The voltage and the anodization time both played significant roles in the formation of TiO2 nanopore-nanotube array film. The optimal voltage was 60 V and the anodization time is less than 30 min by anodizing Ti films in ethylene glycerol containing 0.5% (w) NH4F and 3% (w) H2O. The growth rate of TiO2 nanotube array was as high as 340 nm/min. Moreover, the photocurrent-potential curves, photocurrent response curves and electrochemical impedance spectra results indicated that the TiO2 nanotube array film with the nanoporous structure exhibited a better photo-response ability and photoelectrochemical performance than the ordinary TiO2 nanotube array film. The reason is that the nanoporous structure on the surface of the nanotube array can separate the photo electron-hole pairs more efficiently and completely than the tubular structure.     

溶胶-凝胶法制备ZnO薄膜及其光催化性能

用溶胶-凝胶法在普通玻璃表面制备了薄膜型ZnO光催化剂,通过XRD、Ab2d、UV-VIS等测试技术对ZnO薄膜进行了表征;以偶氮胭脂红为降解物,考察了薄膜退火温度、镀膜层数、溶液初始质量浓度和反应体系初始pH值对ZnO薄膜光催化性能的影响,并进行了相关机理的探讨．研究表明：溶胶-凝胶法制备的ZnO薄膜呈透明状,薄膜表面均匀分布着球形ZnO晶粒;随着退火温度的升高,ZnO晶粒在17～30mm范围内逐渐增大．光催化实验中ZnO薄膜光催化降解偶氮胭脂红的最佳工艺条件是：退火温度为300℃,镀膜层数为5层,溶液初始pH值为8～9．     

Thermal evolution of morphological,optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Plasmonic nanocomposite thin films find exciting applications in environmental remediation and photovoltaics. We report on thermal annealing driven development of morphology, structure and photocatalytic performance of Au–Cu₂O–CuO nanocomposite thin film. Nanocomposite thin film coatings of Au–Cu₂O–CuO, prepared by radio frequency (RF) magnetron co-sputtering, were annealed at different temperatures. Thermal annealing driven evolution of morphology of Au–Cu₂O–CuO nanocomposite was studied by field emission scanning electron microscopy (FESEM), which revealed significant growth in size of nanostructures from 10 nm to 69 nm upon annealing. X-ray diffraction (XRD) together with Raman studies confirmed the nanocomposite nature of Au–Cu₂O–CuO film. UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) studies showed band gap variation from 2.44 eV to 1.8 eV upon annealing at 250 °C. Nanocomposite thin film annealed at 250 °C exhibited superior photocatalytic activity for organic pollutants [methylene blue (MB) and methyl orange (MO)] decomposition. The origins of thermal transformation of morphological, optical and photocatalytic behaviour of the Au–Cu₂O–CuO nanocomposite coating are discussed.

     

Material and sensing properties of Pd-deposited WO3 thin films

The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.     

Influence of thermal annealing on microstructural,morphological, optical properties and surface electronic structure of copper oxide thin films

In this study, effect of the post-deposition thermal annealing on copper oxide thin films has been systemically investigated. The copper oxide thin films were chemically deposited on glass substrates by spin-coating. Samples were annealed in air at atmospheric pressure and at different temperatures ranging from 200 to 600°C. The microstructural, morphological, optical properties and surface electronic structure of the thin films have been studied by diagnostic techniques such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–VIS) absorption spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The thickness of the films was about 520 nm. Crystallinity and grain size was found to improve with annealing temperature. The optical bandgap of the samples was found to be in between 1.93 and 2.08 eV. Cupric oxide (CuO), cuprous oxide (Cu₂O) and copper hydroxide (Cu(OH)₂) phases were observed on the surface of as-deposited and 600 °C annealed thin films and relative concentrations of these three phases were found to depend on annealing temperature. A complete characterization reported herein allowed us to better understand the surface properties of copper oxide thin films which could then be used as active layers in optoelectronic devices such as solar cells and photodetectors.     

TiO2 thin films for dyes photodegradation

The aim of the present study is to investigate the influence of the TiO₂ specific surface (powder, film) on the photocatalytic degradation of methyl orange. Porous TiO₂ films were deposited on transparent conducting oxide substrates by spray pyrolysis deposition. The films were characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy, and the UV-Vis spectroscopy. The XRD spectra of nanoporous TiO₂ films revealed an anatase, crystalline structure that is known as the most suitable structure in photocatalysis. The average thickness of the films was 260 nm and the measured band gap is 3.44 eV. The influence of the operational parameters (dye concentration, contact time) on the degradation rate of the dye on TiO₂ was examined. There were calculated the kinetic parameters and the process efficiency. Using thin films of TiO₂ is technologically recommended but raises problems due to lowering the amount of catalyst available for the dye degradation.     

Nanoporous titanium oxide synthesized from anodized Filtered Cathodic Vacuum Arc Ti thin films

This paper describes the formation of self-organized nanopores in thin films of titanium prepared using a Filtered Cathodic Vacuum Arc (FCVA) deposition system. The post-deposition anodization was performed using 0.5% (wt) NH₄F in ethylene glycol and an aqueous based solution containing 0.5% (wt) NH₄F and 1 M (NH₄)₂SO₄ electrolytes. Homogenously distributed nanopores with dimensions in the range of 10 to 20 nm were obtained. Nanoporous TiO₂ thin films were obtained after annealing the anodized samples at 600 °C for 4 h. Scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize these nanoporous films. Raman measurements revealed that the rutile TiO₂ polymorph dominates these structures along with imperfect titanium oxidation resulting in the formation of defect structures, particularly when aqueous electrolyte was used for the anodization.     

The effect of sputtering gas pressure on structure and photocatalytic properties of nanostructured titanium oxide self-cleaning thin film

Titanium oxide thin films were deposited by DC reactive magnetron sputtering on ZnO (80 nm thickness)/soda-lime glass and SiO₂ substrates at different gas pressures. The post annealing on the deposited films was performed at 400 °C in air atmosphere. The results of X-ray diffraction (XRD) showed that the films had anatase phase after annealing at 400 °C. The structure and morphology of deposited layers were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface grain size and roughness of TiO₂ thin films after annealing were around 10-15 nm and 2-8 nm, respectively. The optical transmittance of the films was measured using ultraviolet-visible light (UV-vis) spectrophotometer and photocatalytic activities of the samples were evaluated by the degradation of Methylene Blue (MB) dye. Using ZnO thin film as buffer layer, the photocatalytic properties of TiO₂ films were improved.     

Nanoporous TiO2 films prepared by thermal rapid treatment (TRT)

Nanoporous TiO₂ films were fabricated by thermal rapid treatment (TRT) of the TiO₂ film which was previously deposited on a substrate by liquid phase deposition. The TiO₂ films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and UV-VIS diffuse reflectance spectroscopy (UV-VIS DRS). Photocatalytic activity of nanoporous TiO₂ coating was assessed by the photocatalytic degradation of methylene blue aqueous solution.     

Preparation of nitrogen co-doped SiO2/TiO2 thin films on ceramic with enhanced photocatalytic activity under visible-light irradiation

In this study, we have successfully deposited N-doped SiO₂/TiO₂ thin films on ceramic tile substrates by sol–gel method for auto cleaning purpose. After dip coating and annealing process the film was transparent, smooth and had a strong adhesion on the ceramic tile surface. The synthesised catalysts were then characterised by using several analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM) and UV-vis absorption spectroscopy (UV-vis). The analytical results revealed that the optical response of the synthesised N-doped SiO₂/TiO₂ thin films was shifted from the ultraviolet to the visible light region. The nitrogen substituted some of the lattice oxygen atoms. The surface area of co-doped catalyst increased, and its photocatalytic efficiency was enhanced. The photocatalytic tests indicated that nitrogen co-doped SiO₂/TiO₂ thin films demonstrated higher than of the SiO₂/TiO₂ activity in decolouring of methylene blue under visible light. The enhanced photocatalytic activity was attributed to an increasing of the surface area and a forming of more hydroxyl groups in the doped catalyst.     

Nitrogen doping of SiC thin films deposited by RF magnetron sputtering

Silicon carbide thin films (Si _x C _y ) were deposited in a RF (13.56 MHz) magnetron sputtering system using a sintered SiC target (99.5% purity). In situ doping was achieved by introducing nitrogen into the electric discharge during the growth process of the films. The N₂/Ar flow ratio was adjusted by varying the N₂ flow rate and maintaining constant the Ar flow rate. The structure, composition and bonds formed in the nitrogen-doped Si _x C _y thin films were investigated by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and Fourier transform infrared spectrometry (FTIR) techniques. RBS results indicate that the carbon content in the film decreases as the N₂/Ar flow ratio increases. Raman spectra clearly reveal that the deposited nitrogen-doped SiC films are amorphous and exhibited C–C bonds corresponding to D and G bands. After thermal annealing, the films present structural modifications that were identified by XRD, Raman and FTIR analyses.     

Low-temperature ozone exposure technique to modulate the stoichiometry of WOx nanorods and optimize the electrochromic performance

A low-temperature ozone exposure technique was employed for the post-treatment of WO(x) nanorod thin films fabricated from hot-wire chemical vapor deposition (HWCVD) and ultrasonic spray deposition (USD) techniques. The resulting films were characterized with x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-vis-NIR spectroscopy and x-ray photoelectron spectroscopy (XPS). The stoichiometry and surface crystallinity of the WO(x) thin films were subsequently modulated upon ozone exposure and thermal annealing without particle growth. The electrochromic performance was studied in a LiClO(4)-propylene carbonate electrolyte, and the results suggest that the low-temperature ozone exposure technique is superior to the traditional high-temperature thermal annealing (employed to more fully oxidize the WO(x)). The optical modulation at 670?nm was improved from 35% for the as-deposited film to 57% for the film after ozone exposure at 150?°C. The coloration efficiency was improved and the switching speed to the darkened state was significantly accelerated from 18.0?s for the as-deposited film to 11.8?s for the film after the ozone exposure. The process opens an avenue for low-temperature and cost-effective manufacturing of electrochromic films, especially on flexible polymer substrates.     

Mounted nanoporous anodic alumina thin films as planar optical waveguides

Solid-supported thin films of self-organized nanoporous anodic aluminum oxide (AAO) have been widely employed for the template preparation of nanostructured functional materials. Recently, the use of nanoporous AAO thin films in optical waveguide spectroscopy (OWS) has been explored for high sensitivity, in situ monitoring of processes occurring within these nanoporous templates. In this contribution, we demonstrate a strategy for mounting bulk anodized AAO thin films on heterogeneous solid-supports suitable for waveguide sensing experiments. Unlike conventional preparations of AAO thin films by anodization of vacuum- or electrochemically deposited Al thin films, the full range of techniques available to anodize bulk Al may potentially be applied with the present method. Moreover, we show that AAO thin films mounted on glass substrates can have superior waveguide coupling properties compared to conventionally prepared samples. The nanostructure of the AAO can be well characterized by an EMT-OWS analysis, demonstrated by comparing scanning electron microscopy images of the AAO and the pore dimensions calculated from an effective medium theory (EMT) analysis of the film refractive index measured by OWS. Finally, using a curved metallic substrate as an example, we show that our mounting technique can be used as a general strategy to functionalize objects with nanoporous AAO films.     

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb_0.92Sr_0.08)(Zr_0.65Ti_0.35)O₃] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350degC and 750degC for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750degC. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature activating significant grain growth for the room-temperature deposited films is about 275degC and the Curie point lies between 325 and 400degC. This relatively high Curie point makes these films suitable for wide temperature range applications.     

Nanopatterned silicon emitters of a solar cell fabricated by anodic aluminum oxide masks

We investigated the nanopattern transferring process by a template of anodic aluminum oxide and the formation of a nanoporous aluminum oxide layer on a Si solar cell by the anodization process of Al thin films. The anodization process provided a template to transfer the nanopattern onto the Si surface. The small-sized nanoporous alumina template was attached to be covered on the textured surface and played the role of etching mask in the F-based dry etching process. Furthermore, we deposited an Al thin film onto the Si surface and the subsequent anodization process was performed. The alumina formulated on the deposited Al thin film did not show the array of nanoporous structure and no nanopatterns were transferred onto the surface. The large-areal alumina deposited on the Si surface showed enhanced photo-absorption in the ultraviolet spectral region of 243 nm, but increased the photo-reflectance in the visible and infrared spectral regions when compared to the Si-bare sample.     

Ti靶及TiO2靶溅射TiO2薄膜微观形貌、结构及光学性质研究

利用射频磁控溅射技术通过Ti靶及TiO2靶在氩氧气氛中同时溅射制备TiO2薄膜,并对所得的样品进行不同温度的退火处理。采用X射线衍射、扫描电子显微镜、拉曼光谱和吸收谱研究了不同的靶材及退火温度对TiO2薄膜晶体结构、微观形貌及光学性质的影响。结果表明:由于靶材的不同,Ti靶溅射时氧分压较低,造成薄膜中存在大量的氧缺陷,晶相发育不完善,颗粒相比TiO2靶溅射时较小,从XRD和拉曼光谱来看,Ti靶溅射得到的TiO2薄膜更有利于金红石相的形成。薄膜的透过率随退火温度的升高而降低,TiO2靶材溅射的薄膜的光学带隙随温度升高而明显降低,而Ti靶得到的薄膜的光学带隙对退火温度的依赖关系不明显。     

A new precursor for the preparation of nanocrystalline TiO2 films and their photocatalytic properties

In this work, we present a new precursor for the preparation of thin and transparent nanocrystalline TiO2 films, which involves the use of Titanium(IV) bis(ammonium lactato) dihydroxide as Ti(IV) source and Triton X-100 as surfactant template. The films were heated at various temperatures in order to optimize their nanostructure and their photocatalytic activity. The morphology and the nanostructure of the films were characterized by SEM and AFM. Crystallinity of the films was examined by XRD and their light absorption with UV-Vis spectroscopy. The photocatalytic activity of the films was investigated by using an azo dye: Basic Blue 41. Excitation of the samples was made by low intensity black light tubes emitting in the Near-UV. The photodegradation of the dye was studied as a function of the quality of the deposited TiO2 films and the calcination temperature in comparison with similar films made by standard procedures.     

Fabrication of hydrogen sensors with transparent titanium oxide nanotube-array thin films as sensing elements

Transparent thin films comprised of highly ordered titania nanotube-arrays were grown from titanium thin films using an anodization technique, from which highly sensitive and selective hydrogen sensors that can operate at room temperature were fabricated. Titanium films sputter deposited on glass at 500 °C were anodized in a fluorine-containing electrolyte to obtain nanotube-array films. Precise monitoring of current during the anodization enabled removal of the samples from the anodization bath at a point where the remaining metal layer became discontinuous, without destroying the nanotube architecture. The samples were then annealed in oxygen at 420 °C to crystallize the nanotube-arrays as well as oxidize any un-anodized metallic regions, yielding transparent films comprised of titanium oxide nanotube-arrays. Herein, we discuss the morphology, structure and optical characterization of these films. When coated with a 10-nm discontinuous palladium layer, the optically transparent nanotube-array films serve as excellent hydrogen sensors, exhibiting a four-order magnitude drop in resistance with exposure to 1000 ppm hydrogen at room temperature.     

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.