Structural characterizations of sol–gel synthesized TiO2 and Ce/TiO2 nanostructures

Mixed phase TiO₂ and Ce/TiO₂ samples were synthesized by a sol–gel method using different hydrolysis conditions. In pure TiO₂ samples, traditional X-ray diffraction (XRD) and Ti K-edge synchrotron X-ray absorption near edge structures (XANES) independently revealed their anatase/rutile phase ratios. XANES results further revealed a substantial amount of Ti atoms existed in other forms beside anatase and rutile TiO₂ in the sample synthesized by the low hydrolysis condition. An increase in the extent of the hydrolysis during the synthesis leads to an increased rutile ratio and a reduction in other forms. In Ce/TiO₂ samples, the crystal sizes were too small for XRD characterization. Only XANES could be used to characterize their phase ratios. It is found that adding Ce impedes rutile formation; leading to increased anatase ratio. The difference in the fundamental aspects of XRD and XANES techniques in providing the phase ratios is discussed.     

Effect of annealing temperature on nanocrystalline TiO2 thin films prepared by sol–gel dip coating method

Nanocrystalline TiO₂ thin films have been prepared by sol–gel dip coating method. X-ray diffraction results showed the formation of anatase phase TiO₂ with grain size in the range of 18–26 nm. The HRTEM studies show that the average particle size of TiO₂ is 24 nm. The EDX analysis confirmed that Ti and O elements are present in the samples. The optical absorption spectra reveal that the absorption edge shifts towards longer wavelength side with increase in annealing temperature.     

Antireflection properties of germanium–carbon coating on zinc supplied substrate

In this research, germanium–carbon coatings were deposited on ZnS and glass substrates by a RF plasma enhanced chemical vapor deposition method using GeH₄ and CH₄ as precursors. ZnS/Ge_1?xC_x double-layer antireflection coating with optical thickness of one quarter wavelength was designed. The samples were characterized by fourier transform infrared spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy and nanoindentation. The coatings exhibited a structure free of pores with a very good adhesion to substrate. Based on the XRD patterns, no diffraction peak was found, so all the coatings mainly had an amorphous structure. The infrared (IR) transmittance spectrum show that the maximum IR transmittance in the band of 1030–1330 cm^?1 was about 84.6%, which is higher than ZnS substrate by 10%. In addition, the reflection of ZnS substrate is about 25%. This system has reduced the reflection from the substrate by 15%.     

光沉积Ru和RuO2的锐钛矿TiO2纳米片的光解水产氧

采用水热法以HF作为结构调控剂合成了主要暴露（001）面的锐钛矿TiO₂纳米片,通过光沉积方法分别合成了负载Ru和RuO₂物种的光催化剂。利用X射线衍射、透射电镜和氢气程序升温还原等分析表征了催化剂的结构性质。通过光解水产氧反应来研究催化剂的催化性能,详细考察了Ru含量、负载方式以及氧化和还原处理等因素的影响,光解水产氧速率的差异证明了Ru物种在不同晶面的电荷-空穴分离效应。与负载单一助催化剂的Ru/TiO₂和RuO₂/TiO₂样品相比,活性最优的0.5%Ru-1.0%RuO₂/TiO₂样品由于负载了双助催化剂,其催化活性得到更大的提高,证实了在锐钛矿TiO₂上的晶面电荷-空穴分离效应.     

Hydrothermal synthesis of CdTe quantum dots–TiO2–graphene hybrid

CdTe–TiO₂–graphene nanocomposites were successfully synthesized via a simple and relatively general hydrothermal method. During the hydrothermal environment, GO was reduced to reduced graphene oxide (RGO), accompanying with the anchoring of TiO₂ nanoparticles on the surface of RGO. In the following process, CdTe quantum dots (QDs) were then in situ grown on the carbon basal planes. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and fluorescent spectroscopy. It is hoped that our current work could pave a way towards the fabrication of QDs–TiO₂–RGO hybrid materials.     

Fabrication of TiO2 μ-donuts by sol-gel spin coating using a polymer mask

TiO₂ μ-donuts have been fabricated on glass and silicon substrates using polymer masks in combination with a sol-gel technique. Cylindrical poly(methyl methacrylate) (PMMA) nanopillars have been created using a composite polymer of polystyrene (PS) and PMMA followed by careful removal of the PS. Atomic force microscopy (AFM) analyses show that the height and diameter of the PMMA cylinders used as the mask are 440 ± 5 nm and 2.1 ± 0.2 μm, respectively. The cylindrical PMMA nanopillars have been coated with the sol of the TiO₂ precursor by a spin coating technique and annealed in air at elevated temperature to remove the PMMA mask. Removal of the PMMA mask has resulted in the formation of well ordered μ-donuts of TiO₂ on silicon surfaces. The interior and exterior heights of the TiO₂ μ-donuts are found to be 373 ± 152 nm and 457 ± 136 nm, respectively; and the interior and exterior diameters of the TiO₂ μ-donuts are found to be 1.33 ± 0.63 μm and 2.82 ± 0.50 μm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of the TiO₂ μ-donuts as well as the smooth TiO₂ thin film showed signals from Ti and O confirming the presence of TiO₂ with Ti 2p_3/2 and O 1s peaks at 458.8 eV and 530.4 eV, respectively. The O 1s peak of the TiO₂ μ-donuts shows another peak at binding energy 532.0 eV due to SiO₂, as during annealing, the PMMA evaporates and the Si substrate is exposed. The X-ray diffractometer (XRD) pattern of the smooth TiO₂ thin film indicates that the anatase phase is present, with the characteristic peaks observed at 2θ values of 25.4°, 37.4°, and 48° corresponding to (1 0 1), (0 0 4), and (2 0 0) planes, respectively. UV-vis absorption spectra of TiO₂ μ-donuts on glass showed an unusual absorption of light in the visible region at ∼524 nm in addition to the usual UV absorption at ∼337 nm.     

Transparent nano composite PVA–TiO2 and PMMA–TiO2 thin films: Optical and dielectric properties

Transparent nano composite PVA–TiO₂ and PMMA–TiO₂ thin films were prepared by an easy and cost effective dip coating method. Al/PVA–TiO₂/Al and Al/PMMA–TiO₂/Al sandwich structures were prepared to study the dielectric behavior. The presence of metal–oxide (Ti–O) bond in the prepared films was confirmed by Fourier transform infrared spectroscopy. X-ray diffraction pattern indicated that the prepared films were predominantly amorphous in nature. Scanning electron micrographs showed cluster of TiO₂ nanoparticles distributed over the film surface and also there were no cracks and pin holes on the surface. The transmittance of the films was above 80% in the visible region and the optical band gap was estimated to be about 3.77 eV and 3.78 eV respectively for PVA–TiO₂ and PMMA–TiO₂ films by using Tauc's plot. The determined refractive index (n) values were between 1.6 and 2.3. High value of dielectric constant (?′ = 24.6 and ?′ = 26.8) was obtained for the prepared composite films. The conduction in the composite films was found to be due to electrons. The observed amorphous structure, good optical properties and dielectric behavior of the prepared nano composite thin films indicated that these films could be used in opto-electronic devices and in thin film transistors.     

Effect of cerium doping on corrosion resistance of amorphous silica–titanium sol–gel coating

The aim of this study was to investigate the effects of ceria doping on corrosion resistance of amorphous silica–titania coating. The microstructural and phase properties of titania–silica and titania–silica–Ceria composite films were investigated by SEM, EDAX and XRD. Potentiodynamic polarization and EIS spectroscopy have been used to study the corrosion behavior of composite coating in 3.5% NaCl solution. Results showed that by cerium doping into silica–titania coating as an inhibitor, the corrosion resistance of the film increased. In addition this study revealed that cerium doping enhanced pitting resistance of the coating.     

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO₂–SiO₂ thin film was prepared by self-assembly method by mixing SiO₂ precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO₂ and even anatase TiO₂ but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO₂ was incorporated into the film. The self-assembly TiO₂–SiO₂ thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO₂ are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO₂:TiO₂) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.     

Surface reconstruction on stishovite SiO2,HfO2 and rutile TiO2 （001）

This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO 2,HfO 2 and rutile TiO 2 (001) by using classical molecular dynamics.It is found that these three surfaces relax instead of reconstruction at 0 K,and have little possibility to reconstruct below 40 K.Above 40 K,surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain.Several reconstruction patterns with approximate surface energies are found,and electrostatic potentials on them are also provided in comparison with possible microscopic results.     

Laser cladding Ni–Co duplex coating on copper substrate

Ni–Co duplex coating has been successfully cladded on copper substrate by continuous wave CO₂ laser. The average microhardness of cladded coating was 635 HV_0.05, which was about 7 times of Cu substrate (92 HV_0.05). During sliding wear tests, the volume loss of copper substrate was about 7 times of Ni–Co duplex coating at 60 min. The high microhardness and crack free advantages of Ni–Co duplex coating, were favorable to reduce the plastic deformation and adhesive wear of copper substrate, resulting in the improvement of wear properties.     

Growth of β-Ga2O3 nanorods by ammoniating Ga2O3/V thin films on Si substrate

This paper reports that/3-Ga2O3 nanorods have been synthesized by ammoniating Ga2O3 films on a V middle layer deposited on Si（111） substrates. The synthesized nanorods were confirmed as monoclinic Ga2O3 by x-ray diffraction,Fourier transform infrared spectra. Scanning electron microscopy and transmission electron microscopy reveal that the grown β-Ga2O3 nanorods have a smooth and clean surface with diameters ranging from 100 nm to 200 nm and lengths typically up to 2μm. High resolution TEM and selected-area electron diffraction shows that the nanorods are pure monoclinic Ga2O3 single crystal. The photoluminescence spectrum indicates that the Ga2O3 nanorods have a good emission property. The growth mechanism is discussed briefly.     

Effects of O2–CO2 polarization beating on femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of O2

Femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy has recently emerged as a promising laser-based temperature-measurement technique in flames. In fs-CARS, the broad spectral bandwidths of the pump and Stokes lasers permit the coupling of each ro-vibrational Raman transition via a large number of pump-Stokes photon pairs, creating a strong Raman coherence. However, the broad-bandwidth fs pulses also excite other molecular transitions that are in resonance. The polarization beating between these closely spaced Raman transitions can affect the coherence dephasing rate of the target molecule, making it difficult to extract accurate medium temperature. In a previous study our group investigated N₂/CO polarization beating in N₂ fs-CARS; in the present work we study O₂/CO₂ polarization beating in O₂ fs-CARS. O₂ fs-CARS can be particularly important for thermometry in non-air-breathing combustion in the absence of N₂. The effects of O₂/CO₂ polarization beating are investigated in the temperature range 300–900 K at atmospheric pressure and also at 300 K for pressures up to 10 bar. Unlike in the N₂/CO system, it was observed in the O₂/CO₂ system that the presence of CO₂ can significantly alter the time evolution of the Raman coherence and, hence, affect the measured temperature.     

Magnetic and structural properties of CaO–SiO2–P2O5–Na2O–Fe2O3 glass ceramics

Magnetic properties of glass ceramics derived from glasses with composition 41CaO·(52−x)SiO₂·4P₂O₅·xFe₂O₃·3Na₂O (2?x?10 mol% iron oxide (Fe₂O₃)) are reported. Structural investigation revealed the presence of nanocrystalline magnetite phase in the heat-treated samples containing x?2 mol% Fe₂O₃. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with a maximum applied field of ±20 kOe as well as a low field of ±500 Oe, in order to evaluate the potential of these glass ceramics for hyperthermia treatment of cancer. Samples with x>2 mol% of iron oxide exhibited magnetic behavior similar to soft magnetic materials with low coercivity. The evolution of magnetic properties in these samples as a function of iron oxide molar concentration is correlated with the amount and crystallite size of magnetite phase present in them.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

脉冲激光辐照TiO2/SiO2薄膜热效应研究

 采用1.06 μm单脉冲激光在不同能量密度下辐照特殊光电系统中典型薄膜光学元件，理论分析了激光辐照薄膜元件产生的温度场和热应力场，在此基础上建立了激光辐照多层薄膜的物理模型，计算软件使用ANSYS软件的热分析模块对激光辐照薄膜元件产生的温度场和热应力场进行了模拟，分别给出不同激光能量密度下薄膜表面光斑中心的温度场、径向温度场和轴向温度场分布；同时给出不同能量密度下薄膜的轴向、径向和环向热应力分布。并对激光辐照薄膜元件产生的温度场、热应力场进行了分析，阐明了原因。     

TiO2/SnO2复合光催化剂的制备及性能

采用特殊液相沉淀法制备纳米级的TiO2/SnO2复合粒子,对制备的纳米TiO2/SnO2采用XRD、TEM等手段进行了表征。用它做催化剂在日光下对甲基橙溶液进行了光催化实验。结果表明,纳米级TiO2/SnO2复合催化剂比纯TiO2的催化活性好,当SnO2摩尔百分数为20%时效果最佳,在60min内对10mg/L的甲基橙水溶液的降解率高达90.2%,具有较好的光催化活性。     

脉冲激光辐照TiO2/SiO2薄膜热效应研究

采用1.06 μm单脉冲激光在不同能量密度下辐照特殊光电系统中典型薄膜光学元件,理论分析了激光辐照薄膜元件产生的温度场和热应力场,在此基础上建立了激光辐照多层薄膜的物理模型,计算软件使用ANSYS软件的热分析模块对激光辐照薄膜元件产生的温度场和热应力场进行了模拟,分别给出不同激光能量密度下薄膜表面光斑中心的温度场、径向温度场和轴向温度场分布;同时给出不同能量密度下薄膜的轴向、径向和环向热应力分布。并对激光辐照薄膜元件产生的温度场、热应力场进行了分析,阐明了原因。     

Thickness dependent activity of nanostructured TiO2/α-Fe2O3 photocatalyst thin films

The effect of thickness of TiO₂ coating on synergistic photocatalytic activity of TiO₂ (anatase)/α-Fe₂O₃/glass thin films as photocatalysts for degradation of Escherichia coli bacteria in a low-concentration H₂O₂ solution and under visible light irradiation was investigated. Nanograined α-Fe₂O₃ films with optical band-gap of 2.06 eV were fabricated by post-annealing of thermal evaporated iron oxide thin films at 400 °C in air. Increase in thickness of the Fe₂O₃ thin film (here, up to 200 nm) resulted in a slight reduction of the optical band-gap energy and an increase in the photoinactivation of the bacteria. Sol-gel TiO₂ coatings were deposited on the α-Fe₂O₃ (200 nm)/glass films, and then, they were annealed at 400 °C in air for crystallization of the TiO₂ and formation of TiO₂/Fe₂O₃ heterojunction. For the TiO₂ coatings with thicknesses ≤50 nm, the antibacterial activity of the TiO₂/α-Fe₂O₃ (200 nm) was found to be better than the activity of the bare α-Fe₂O₃ film. The optimum thickness of the TiO₂ coating was found to be 10 nm, resulting in about 70 and 250% improvement in visible light photo-induced antibacterial activity of the TiO₂/α-Fe₂O₃ thin film as compared to the corresponding activity of the bare α-Fe₂O₃ and TiO₂ thin films, respectively. The improvement in the photoinactivation of bacteria on surface of TiO₂/α-Fe₂O₃ was assigned to formation of Ti-O-Fe bond at the interface.