Formation and dissolution of copper-based nanoparticles in SiO2 sol-gel film using heat treatment and/or UV light exposure

We report in this paper, results on the formation and dissolution of Cu-based nanoparticles in sol-gel SiO₂ thin films using heat treatment and UV light exposure, respectively. Using UV-vis-NIR spectroscopy, we have shown that Cu₂O nanoparticles can be generated by controlling the aging of the sol prior to film deposition while the Cu⁰ nanoparticles can be synthesized using a heat treatment in H₂ atmosphere at 550 °C for 6 h. It has been also demonstrated that irradiation with an UV pulsed (Q-switched Nd:YAG) or continuous black ray UV lamp can dissolve these Cu-based nanoparticles with controlled, spatial selectivity. The mechanism of the dissolution process was found to be mainly thermal. Finally, we report a new analytical technique for detecting/confirming the presence of low densities of Cu nanoparticles in the films, based on a relative heat flow measurement of such films using a micro-thermal analyzer (e.g., TA Instruments μTA model 2990).     

Effect of tungsten on the electrochromic behaviour of sol-gel dip coated molybdenum oxide thin films

The paper describes the results obtained on the performance of Mo oxide and mixed W/Mo oxide thin films for possible electrochromic applications. Mo and W/Mo oxide films were deposited on conductive (FTO) glass substrates using sol-gel dip coating method. The films were annealed at 250 °C for 30 min. The structure and morphology of Mo and W/Mo oxide films were examined using XRD, SEM and EDS. XRD results indicate the amorphous nature of the Mo and W/Mo oxide films annealed for 30 min. The CV measurements revealed that the films prepared with 10 wt.% of tungsten exhibit maximum anodic/cathodic diffusion coefficient of 24.99/12.71 × 10⁻¹¹ cm²/s. The same film exhibits a maximum transmittance variation (ΔT%) of 83.4% at 630 nm and 81.06% at 550 nm with the optical density of 1.00 and 1.13 respectively.     

Effect of interface energy on abnormal grain growth in pyrite films prepared by sol-gel method

The pyrite films were prepared on quartz and glass substrates by the sol-gel dip coating process and sulfuration treatment. The film microstructure, chemical composition and morphology dependent on sulfuration temperature were investigated. The sulfuration treatment at 773-923 K for the films prepared by the sol-gel dip coating process can prepare pyrite films. Some grains show abnormal growth during sulfuration treatment. The grain size of abnormal growth increased to a limited value with increasing the sulfuration temperature. The grain size in pyrite films has bimodal distribution. The first peak is of Lognormal distribution and the second peak Gauss distribution. By determination of the abnormal grain growth activation energy, it can be concluded that the reduction in interface energy at the interface between the substrate and film should be responsible for the grain abnormal growth.     

Reversible transformations of silver oxide and metallic silver nanoparticles inside SiO2 films

Reversible transformation of silver oxide and metallic nanoparticles inside a relatively porous silica film has been established. Annealing of Ag-doped films in oxidizing (air) atmosphere at 450 °C yielded colorless films containing AgO_x. These films were turned yellow when heated in H₂-N₂ (reducing atmosphere) due to the formation of Ag nanoparticles. This yellow coloration (due to nano Ag⁰) and bleaching (conversion of Ag⁰ → Ag⁺) are reversible. Optical and photoluminescence spectra are well consistent with this coloration and bleaching. The soaking test of the air-annealed film in Na₂S₂O₃ solution supports the presence of Ag⁺. Grazing incidence X-ray diffraction and transmission electron microscopy studies reveal the formation of Ag-oxides and Ag nanoparticles in the oxidized and reduced films, respectively.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Dielectric and ferroelectric properties of Ba(Sn0.15Ti0.85)O3 thin films grown by a sol-gel process

Ferroelectric Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were deposited on LaNiO₃-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 × 10⁻⁷ A/cm² and 5 × 10⁻⁵ A/cm² and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.     

2D spinodal phase-separated TiO2 films prepared by sol-gel process and photocatalytic activity

For the purpose of obtaining oxide thin films with high photocatalytic activity, we have successfully prepared the TiO₂ anatase polycrystalline films with a two-dimensional spinodal phase-separated structure (2D-SPSS) in micron size by the sol-gel dip-coating method from a titanium tetraisopropoxide solution containing polyoxyethylene(20) nonylphenyl ether. It has been also found that TiO₂ films with a variety of morphologies in addition to the 2D-SPSS can be formed by controlling the molar ratio of water to titanium tetraisopropoxide. The methylene blue photodegradation activity of the 2D-SPSS TiO₂ film was higher than that of dense TiO₂ film prepared from a TiO₂ sol without co-existing polymer. This fact can be interpreted in terms of possessing a high specific surface area available for the photocatalytic reaction.     

Preparation and hydrophilicity of TiO2 sol-gel derived nanocomposite films modified with copper loaded TiO2 nanoparticles

In this study, TiO₂ nanocomposite films with 10 g/L of TiO₂ and copper loaded TiO₂ nanoparticles as nanofillers were deposited on the glass substrates using the sol gel dip-coating method. FE-SEM and UV-vis spectrophotometer were used to evaluate morphological and optical properties of copper loaded titania nanoparticles. In addition, XPS and water contact angle techniques were used to study the surface properties and superhydrophilicity of titania nanocomposite films, respectively. The results indicated that copper loaded TiO₂ nanoparticles had a significant effect on the hydrophilicity of nanocomposite film and maintaining it in a dark place for a long time (6.2 degree for titania nanocomposite films with copper loaded nanoparticle and 23.7 degree for nanocomposite film with titania nanoparticles).     

Electrical properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films on TiO2 buffer layer

Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ antiferroelectric thin films with thickness of 500 nm were successfully deposited on TiO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates via sol-gel process. Microstructure of Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was studied by X-ray diffraction analyses. The antiferroelectric nature of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ thin films was confirmed by the double hysteresis behaviors of polarization and double buffer fly response of dielectric constant versus applied voltage at room temperature. The capacitance-voltage behaviors of the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films with and without TiO₂ buffer layer were studied, as a function of temperature. The temperature dependence of dielectric constant displayed a similar behavior and the Curie temperature (T_c) was 193 °C for films on both substrates. The current caused by the polarization and depolarization of polar in the Pb_0.97La_0.02(Zr_0.95Ti_0.05)O₃ films was detected by current density-electric field measurement.     

Structure and dielectric performance of K-doped (Pb0.5Ba0.5)ZrO3 thin films

In the present investigation (Pb_0.5Ba_0.5)ZrO₃ (PBZ) thin films doped by K (KPBZ) from 0 to 5 mol% were successfully deposited on Pt-buffered silicon substrates by a sol-gel method. The K content dependence of microstructure and electrical properties of KPBZ thin films were studied in detail. It was found that, although all the films displayed a pure perovskite structure without obvious difference, the surface roughness of KPBZ films was decreased with increasing K content. Dielectric measurements showed that the figure of merit (FOM) values of KPBZ thin films were greatly increased by K-doping, and at the same time that the temperature-dependent stability was also improved. Thus, K doping is a promising way to optimize the overall electrical properties of PBZ thin films for potential application in tunable devices.     

Insulating properties of rapid thermally processed Bi2Ti2O7 thin films by a chemical solution decomposition technique

Crack-free Bi₂Ti₂O₇ thin films on silicon substrates were prepared using chemical solution decomposition technique, and then treated by rapid thermal annealing. The microstructure of the films was studied by scanning electron microscopy. The effects of different fabricating procedures and various annealing temperatures and times on the leakage current density were investigated. The results show that the leakage current density decreases with increasing annealing temperature, while increases with increasing annealing time. Annealing temperature has a much stronger effect on the insulating properties of Bi₂Ti₂O₇ thin films than that of annealing time.     

Effect of thermal annealing treatment on structural, electrical and optical properties of transparent sol-gel ZnO thin films

Effect of thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films are studied. XRD results show that the annealed ZnO films with wurtzite structure are randomly oriented. Crystallite size, carrier concentration, resistivity and mobility are found to be dependent on the annealing temperature. The change in carrier concentration is discussed with respect to the removal of adsorbed oxygen from the grain boundaries. The highest carrier concentration and lowest resistivity are 8 × 10¹⁸ cm⁻³ and 2.25 × 10⁻¹ Ω cm, respectively, for the film annealed at 500 °C in vacuum. The annealed films are highly transparent with average transmission exceeding 80% in the wavelength region of 400-800 nm. In all three ambients, the optical band gap value does not change much below 500 °C temperature while above this temperature band gap value decreases for nitrogen and air and increases for vacuum.     

Structure and optical properties of AlxZn1−xO alloys by sol-gel technique

Al_xZn_1−xO (x = 0-0.5) thin films were prepared on quartz glass substrates by sol-gel technique. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed for microstructure characterization of these thin films. In films with up to 20 at.% Al incorporation, compound nano-crystal phase was observed while wurtzite structure disappeared. Zn3d electron binding energy and Zn LMM‘s chemical shift were both increased by more than 0.4 eV. Transmittance spectra revealed that these films possessed high transmittance in the visible region, and the end of UV absorption edge shifted to less than 300 nm when Al content exceeds 20 at.% due to quantum confinement effect.     

Deposition of transparent conductive mesoporous indium tin oxide thin films by a dip coating process

Cetyltrimethyl ammonium bromide (CTAB) templated mesoporous indium tin oxide (ITO) thin films were deposited on quartz plates by an evaporation-induced self-assembly (EISA) process using a dip coating method. The starting solution was prepared by mixing indium chloride, tin chloride, and CTAB dissolved in ethanol. Five to fifty mole percent Sn-doped ITO films were prepared by heat-treatment at 400 °C for 5 h. The structural, adsorptive, electrical, and optical properties of mesoporous ITO thin films were investigated. Results indicate that the mesoporous ITO thin films have an ordered two-dimensional hexagonal (p6mm) structure, with nanocrystalline domains in the inorganic oxide framework. The continuous thin films have highly ordered pore sizes (>20 Å), high Brunauer-Emmett-Teller (BET) surface area up to 340 m²/g, large pore volume (>0.21 cm³/g), outstanding transparency in the visible range (>80%), and show a minimum resistivity of ρ = 1.2 × 10⁻² Ω cm.     

Polarization fatigue and photoinduced current in (Pb0.72La0.28)Ti0.93O3 buffered Pb(Zr0.52Ti0.48)O3 films on platinized silicon

We report a study on the fatigue behavior of Pb(Zr_0.52Ti_0.48)TiO₃ (PZT) films deposited on Pt/Ti/SiO₂/Si substrates by a sol-gel method with single- and double-sided (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) buffer layers, with an attempt to clarify the role of the top and bottom PLT buffer layers on the fatigue endurance (FE) of the PZT films. It is revealed that the existence of the PLT buffer layer and the level of driving alternating-current electric switching field strongly influence the fatigue properties. In terms of the existence of an asymmetric built-in electric field near the top and bottom interfaces between the film and metal electrode, we explain the observed fatigue properties.     

Nonaqueous sol-gel synthesis and growth mechanism of single crystalline TiO2 nanorods with high photocatalytic activity

In this paper, we report on a nonaqueous synthesis of single crystalline anatase TiO₂ nanorods by reaction between TiCl₄ and benzyl alcohol at a low temperature of 80 °C. The resulting samples were characterized with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectrometry and UV-vis diffuse reflectance spectroscopy. We proposed that the TiO₂ nanorods were formed through an oriented attachment mechanism. More importantly, these single crystalline anatase TiO₂ nanorods exhibited significantly higher photocatalytic activities than commercial photocatalyst P25. This study provides an environmentally friendly and economic approach to produce highly active TiO₂ photocatalyst.     

Luminescent properties of Gd2Ti2O7: Eu phosphor films prepared by sol-gel process

Gd₂Ti₂O₇: Eu³⁺ thin film phosphors were fabricated by a sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800 °C and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. The doped Eu³⁺ showed orange-red emission in crystalline Gd₂Ti₂O₇ phosphor films due to an energy transfer from Gd₂Ti₂O₇ host to them. Both the lifetimes and PL intensity of the Eu³⁺ increased with increasing the annealing temperature from 800 to 1000 °C, and the optimum concentrations for Eu³⁺ were determined to be 9 at.%. of Gd³⁺ in Gd₂Ti₂O₇ film host.     

Fabrication of hollow silver spheres by MPTMS-functionalized hollow silica spheres as templates

In this study, we provide a strategy to prepare the hollow silver spheres by accumulating the silver nanoparticles on the surface of 3-mercaptopropyltrimethoxysilane (MPTMS)-functionalized silica as templates, which was accomplished by the chemisorption between silver nanoparticles and thiol groups. Then, the resulting hollow silver spheres were obtained through the chemical wet etching process with 10 M HF solution. In conventional method, the fabrication of hollow silver spheres from core-shell spheres was not easy due to the difficulties in retaining the shell structures during core removal. The method in this paper could overcome this limitation. The major focus of study is on understanding the mechanism of formation of the hollow silver spheres through the self-assembly behavior by chemisorption between silver nanoparticles and thiol groups. The silver-coated silica and hollow silver spheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and X-ray photoelectron spectroscopy (XPS).     

An aqueous sol-gel synthesis of chromium(III) doped mesoporous titanium dioxide for visible light photocatalysis

Nanoparticles of titanium dioxide doped with Cr³⁺ ions have been prepared through an aqueous sol-gel method. The mesoporous nature of both pure and Cr³⁺ doped TiO₂ powders, with specific surface area of 7.4 and 6.6 m² g⁻¹, respectively, is maintained even at calcination temperature of 800 °C. The transformation of TiO₂ from the anatase to rutile phase is suppressed up to 800 °C by Cr³⁺ ion doping. Even though surface area values are decreased, the doped materials show improved photocatalytic activity, which may be due to increased crystallinity of the anatase phase without the formation of rutile. Doped materials have a red-shift in the band gap energy and hence, photoactivity under visible light. The rate of photodegradation of methylene blue dye for both pure and doped TiO₂ under visible light has been monitored in this study. The 0.25 mol% Cr(III) doped photocatalyst, calcined at 800 °C, shows the highest photocatalytic activity under visible light with a rate constant of ∼15.8 × 10⁻³ min⁻¹, which is nearly three times higher than that of commercially available Degussa P25 titania (5.8 × 10⁻³ min⁻¹).     

Improved properties of GRC composites using commercial E-glass fibers with new coatings

A study was carried out to evaluate the action of a new 15CaO-15BaO-20SiO₂-50TiO₂ coat on long-term durability of glass fiber reinforced cement. Compressive strength, flexural strength and drying shrinkage were measured. Significant improvement was observed and four reasons were given to explain it. The results testify further the effectiveness of the alkali resistance of the new coat.