IR Spectroscopic Investigations of Gasochromic and Electrochromic Sol-Gel—Derived Peroxotungstic Acid/Ormosil Composite and Crystalline WO3 Films

We studied the gasochromic effect of amorphous peroxopolytungstic acid (W-PTA), W-PTA (ormosil) and crystalline WO₃ films. These latter films were prepared after a heat treatment of W-PTA/ormosil films at 450°C. The ormosil served as a template, providing the monoclinic WO₃ films with adequate porosity. The spill-over effect was attained by impregnating the porous WO₃ crystalline films with H₂PtCl₆ followed by a heat treatment at 380°C. The amorphous films became gasochromic with the addition of PdCl₂ to the corresponding W-PTA and W-PTA/ormosil sols.Structural features of all the films were studied with the help of infrared (IR) spectroscopy and transmission electron microscopy (TEM). In situ IR spectra of the films, performed in the presence of reducing (H₂/Ar) and oxidising (O₂/Ar) gases, revealed a reversible transformation of the monoclinic to the tetragonal H _x WO₃ phase. At the same time the coloration (reduction) of the amorphous films was accompanied by the formation of coordinated water molecules and increased numbers of W=O bonds. Gasochromic colouring/bleaching changes and the corresponding kinetics were assessed from in situ UV-visible transmission measurements on the films.     

Interface characteristics of thin liquid films in a charged lubricated contact

The interface characteristics of liquid films confined within a nanogap between a steel ball and a smooth glass disk after exposing to an external electric field (EEF) are reported in the paper. The emergence of micro‐bubbles induced by the EEF has been found to be closely related with the electric current flow at both a positive EEF and a negative EEF. The polarity effect of the variation in the electric current flowing through a polar liquid film over time is more pronounced than that through a nonpolar liquid film. The surface of the contacting pair with the polar liquid film confined after the removal of the EEF is more severely damaged at a negative EEF, while no indication of damage has been observed on the surface contacting the nonpolar liquid film at either polarity. The bubbles generated under a positive EEF can collapse more readily than those generated under a negative EEF. Different mechanisms of these experimental phenomena have been discussed in the paper. Copyright © 2014 John Wiley & Sons, Ltd.     

Quasi-solid-state dye-sensitized solar cell based on a polymer gel electrolyte with in situ synthesized ionic conductors

A polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors was prepared for fabricating a quasi-solid-state dye-sensitized solar cell (QS-DSSC). The in situ synthesized Acac-Py-I₂ ionic conductors show weaker influence on the liquid electrolyte absorbency of the polymer gel electrolyte than that of Acac-Py-I₂ ionic conductors dissolved in liquid electrolyte. Owing to the higher liquid electrolyte absorbency, the polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors shows higher ionic conductivity than that of polymer gel electrolyte with Acac-Py-I₂ ionic conductors absorbed from liquid electrolyte. QS-DSSC containing the polymer gel electrolyte with in situ synthesized Acac-Py-I₂ ionic conductors shows 3.815% energy conversion efficiency, which is 21.6% higher than that of QS-DSSC containing polymer gel electrolyte with Acac-Py-I₂ ionic conductors absorbed from liquid electrolyte.     

Solid-state pH ultramicrosensor based on a tungstic oxide film fabricated on a tungsten nanoelectrode and its application to the study of endothelial cells

In this paper, preparation of a novel pH ultramicrosensor and its physiological application has been discussed. A tungsten nanoelectrode was produced by an etching method in 0.1 mol/l NaOH solution at the potential of +0.4 V (versus Ag/AgCl reference electrode) for about 100 s and the diameters ranged from 500 to 800 nm. The pH ultramicrosensor was fabricated by producing WO₃ at W nanoelectrode surface by electrooxidation in 2.0 mol/l H₂SO₄ solution between 1.0 and 2.0 V. At last, Nafion was coated on the surface of WO₃ to protect the pH ultramicrosensor. The W/WO₃ pH ultramicrosensor exhibited a good pH linear region from 2.0 to 12.0 with a super-Nernstian slope of −53.5 ± 0.5 mV/pH unit. Response times ranged from 3 s at about pH 6.0-7.0 up to 15 s at high pH. An interference of various ions to the pH measurement was also studied in this paper. We also studied the lifetime, stability and reproducibility of the W/WO₃ pH ultramicrosensor. In order to testing the performance of W/WO₃ ultramicrosensor, we applied it to measure the extracellular pH values and a pH variation was also given about the normal, damaged and recovery endothelial cells.     

Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides

Thin films of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet-visible (UV-VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n_∥ = 1.806 and the out-of-plane index n_⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA-PDA chains to align along the film plane. The frequency dispersion of the in-plane refractive index n_∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV-visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,^?1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in-plane refractive index n_∥. Tilt-angle–dependent polarized IR results indicate nearly the same increase for the out-of-plane index n_⊥. Application of the Maxwell relation then leads to the out-of-plane dielectric constant ε^⊥ ? 2.7 at 1.2 × 10¹³ Hz, as compared with the measured value of ca. 3.0 at 10⁶ Hz. Assuming this small difference to remain the same for the in-plane dielectric constants ε_∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant ε_∥ ? 3.4 at 1.2 × 10¹³ Hz, and ε_∥ ? 3.7 at 10⁶ Hz. © 1992 John Wiley & Sons, Inc.     

Optimization of the synthesis and characterizations of chemical bath deposited Cu2S thin films

Semiconducting copper sulphide (Cu₂S) thin films have been deposited on various substrates (SnO₂:F/glass, glass) by the simple and economical chemical bath deposition technique. The depositions were carried out during a deposition time of about 32.5 min in the pH range of 9.4 to 11. The synthesized Cu₂S thin films were characterized using various techniques without any annealing treatment. X-ray diffraction study shows that Cu₂S films exhibit the best crystallinity for pH = 10.2. For this pH value, Auger electron spectroscopy investigations show that Cu₂S thin films grown on an SnO₂/glass substrate exhibit stochiometric composition with [Cu]/[S] concentrations ratio equal to 2.02. Using the Kelvin method, the work function difference (Ф_material– Ф_probe) for the Cu₂S films deposited on SnO₂/glass substrates at the optimum pH value was found to be equal to 145 meV. Hall measurements confirm the p-type electrical conductivity of the obtained films. The electrical resistivity was of the order of 3.85 × 10⁻⁴ Ω-cm. The transmission and reflection coefficients vary in the range of [35–60] % and [5–15] % respectively, in the visible range, and the band gap energy is about 2.37 eV.     

Enhanced ferroelectric properties of Ce-substituted BiFeO<Subscript>3</Subscript> thin films prepared by sol–gel process

Ce-substituted BiFeO₃ film (BCFO film) have been prepared by sol–gel process on F doped SnO₂ (FTO)/glass substrates. The effects of Ce substitution on the structural and electrical properties have been reported. X-ray diffraction data confirmed the R3c structure with the elimination of all secondary phases. We observed an increase in the remnant polarization (Pr) with Ce substitution and obtained a maximum value of ∼84 μC/cm² in 5% Ce-substituted film. The dielectric constant of the films was increased from 280 to about 420 for the BiFeO₃ film and 5% Ce-substituted BCFO film, respectively and the films showed excellent dielectric loss behavior. Moreover, the leakage current was substantially reduced by the Ce substitution.     

Understanding and improving the deposition conditions of SiO2 thin films obtained by ultrasonic sol-gel procedure

Sol-gel deposition of an ultrasonically atomized aerosol has been proven to be a convenient thin film deposition method. Flexibility of the ultrasonic process allows the use of a large range of source solutions. In this paper we describe and discuss the deposition conditions of SiO₂ films. The chemical parameters are contemplated and we discuss the influence of ultrasonic waves on the reliability of our process. Source solutions and SiO₂ film properties are studied by viscosimetry, Fourier Transform IR spectroscopy and spectroscopic ellipsometry.     

Microstructure and electrical-optical properties of cesium tungsten oxides synthesized by solvothermal reaction followed by ammonia annealing

Cesium tungsten oxides (Cs_xWO₃) were synthesized by solvothermal reactions using ethanol and 57.1 vol% ethanol aqueous solution at 200 °C for 12 h, and the effects of post annealing in ammonia atmosphere on the microstructure and electrical-optical properties were investigated. Agglomerated particles consisting of disk-like nanoparticles and nanorods of Cs_xWO₃ were formed in the pure ethanol and ethanol aqueous solutions, respectively. The samples retained the original morphology and crystallinity after annealing in ammonia atmosphere up to 500 °C, while a small amount of nitrogen ion were incorporated in the lattice. The as-prepared Cs_xWO₃ sample showed excellent near infrared (NIR) light shielding ability as well as high transparency in the visible light region. The electrical resistivity of the pressed pellets of the powders prepared in pure ethanol and 57.1 vol% ethanol aqueous solution greatly decreased after ammonia annealing at 500 °C, i.e., from 734 to 31.5 and 231 to 3.58 Ω cm, respectively.     

Structural and nanomechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Perovskite (K, Na)NbO₃ (KNN) thin films (~100 nm) were prepared by sol–gel/spin coating process on Pt/SiO₂/Si substrates and annealed at 650 °C. The structural properties of KNN films were confirmed by X‐ray diffraction analysis (XRD), Raman spectroscopy and scanning electron, transmission electron and atomic force microscopy (SEM, TEM and AFM) analysis. Pure perovskite phase of K_0.65Na_0.35NbO₃ in nonstoichiometric composition with monoclinic symmetry in film was revealed. Uniform homogeneous microstructure of KNN film with the roughness (~6.9 nm) contained spherical particles (~50–90 nm). Nanoindentation technique was used to characterize the mechanical properties of KNN films. Elastic modulus and hardness of Pt, SiO₂ and KNN thin films were calculated from their composite values of KNN/Pt/SiO₂/Si film/substrate system. The modulus and hardness of KNN film (71 and 4.5 GPa) were lower in comparison with SiO₂ (100 and 7.5 GPa). Pt film (~30 nm) did not influence the composite modulus, but had effect on hardness of KNN film. Copyright © 2015 John Wiley & Sons, Ltd.     

Deposition and investigation of lanthanum-cerium hexaboride thin films

Thin films of lanthanum-cerium hexaboride, the promising thermoelectric material for low-temperature applications, are deposited on various substrates by the electron-beam evaporation, pulsed laser deposition and magnetron sputtering. The influence of the deposition conditions on the films X-ray characteristics, composition, microstructure and physical properties, such as the resistivity and Seebeck coefficient, is studied. The preferred (100) orientation of all films is obtained from XRD traces. In the range of 780-800 °C deposition temperature the highest intensity of diffractions peaks and the highest degree of the preferred orientation are observed. The temperature dependence of the resistivity and the Seebeck coefficient of films are investigated in the temperature range of 4-300 K. The features appropriate to Kondo effect in the dependences ρ(T) and S(T) are detected at temperatures below 20 K. Interplay between the value of the Seebeck coefficient, metallic parameters and Kondo scattering of investigated films is discussed.     

Orientation control of perovskite thin films on glass substrates by the application of a seed layer prepared from oxide nanosheets

Orientation control of perovskite compounds was investigated by the application of a seed layer prepared from oxide nanosheets. An aqueous suspension of oxide nanosheets was prepared by the exfoliation of a layered compound of KCa₂Nb₃O₁₀ oxide grains. A seed layer composed of (TBA)Ca₂Nb₃O₁₀ nanosheets (TBA = tetrabutylammonium) was formed on a glass substrate by simply dip coating it in the suspension. Two kinds of perovskite compounds, LaNiO₃ (LNO) and Pb(Zr,Ti)O₃ (PZT) with a preferred orientation of (00l) were successfully grown on this seeded glass substrate. In this study, the relation between lattice mismatch and electrical properties is investigated. A large, oriented PZT film with a size of 5 ×4 cm shows an improved P-E hysteresis behavior by use of this orientation control.     

Growth of semiconducting iron sulfide thin films by chemical vapor deposition from air-stable single-source metal organic precursor for photovoltaic application

Semiconducting nanostructured iron sulfide thin films were prepared by aerosol chemical vapor deposition at 673 and 723?K from newly synthesized iron complex of dithiocarbo-1,2,3,4-tetrahydroquinoline [Fe(S₂CNC₉H₁₀)₂]. The degree of film surface roughness was determined by atomic force microscopy. The nature of the deposited thin films formed was determined by a combination of EDX analysis and glancing angle X-ray diffraction.     

The role of thermal analysis in optimization of the electrochromic effect of nickel oxide thin films, prepared by the sol–gel method: Part II

Thin films and the corresponding xerogels were prepared from nickel acetate precursor using the sol–gel dip-coating technique. The differences in thermal stability of the two forms of samples were studied by dynamic and isothermal thermogravimetry. For thin films, the onset decomposition temperature of acetate groups was 230 °C and for the xerogel 250 °C. During thermal decomposition, the formation of nanosized nickel oxide took place. Carbonate ions, which were formed during thermal decompostion of acetate groups, remained either free or bidentately coordinated to nickel. In situ monochromatic optical transmittance changes showed that an optical stability up to the 100th cycle was already achieved for films heated for 15 min at the isothermal temperature (thermal decompositon 25%). Comparison of the results obtained for nickel sulfate (Part I) and nickel acetate precursors shows that at least two parameters, the precursor used and the degree of thermal treatment, have considerable influence on the thermal stability of the thin film and also on its electrochromic response during the cycling process.     

Gelation of a liquid electrolyte with aniline for use in a quasi-solid-state dye-sensitized solar cell

A new kind of gel electrolyte containing only organic solvents and an iodide salt-namely 3-methoxypropionitrile(MPN),aniline and AlI 3 -has been prepared.Gel formation results from the Lewis acid-base interaction between the Lewis acid ionic conductor AlI 3 and the Lewis base organic solvent aniline and no additional gelling agent is required.The AlI 3-aniline complex acts both as an ionic conductor and as a gelling agent.The differences between the peaks characteristic of the-NH 2 group and aromatic ring in the FTIR spectra of free aniline and the AlI 3-aniline hybrid confirm the formation of the AlI 3-aniline complex.The photovoltaic performance and long-term stability of dye-sensitized solar cells can be greatly enhanced by the addition of aniline to the AlI 3-MPN liquid electrolyte.     

一种不含胶凝剂的凝胶电解质在准固态染料敏化太阳能电池中的应用

报道了一种不含胶凝剂的凝胶电解质的制备及在准固态染料敏化太阳能电池中的应用.这种新型凝胶电解质仅含有机溶剂和碘盐,即3-甲氧基丙腈、苯胺、三碘化铝和碘.上述混合物通过路易斯酸性三碘化铝离子导体和路易斯碱性苯胺有机溶剂间的路易斯酸-碱相互作用形成凝胶,无需额外添加传统凝胶电解质的关键组分—胶凝剂.形成的三碘化铝-苯胺复合物在凝胶电解质中能同时发挥离子导体和胶凝剂的作用.红外光谱图中苯胺的氨基和苯环特征峰的变化证实了三碘化铝-苯胺复合物的形成.含这种新型凝胶电解质的准固态染料敏化太阳能电池光电性能和稳定性与含三碘化铝-3-甲氧基丙腈液体电解质的染料敏化太阳能电池相比有很大提高.     

Optimization of the photocatalytic activity of CdO + CdTiO3 coupled oxide thin films obtained by sol-gel technique

In the preparation of CdO + CdTiO₃ polycrystalline thin films by the sol-gel method, the optical, structural and crystalline properties, as well as the photocatalytic activity (PA) depends strongly on the sintering temperature (Ts) of the films and of the Ti/Cd ratio used in the precursor solution. In this work, CdO + CdTiO₃ thin films were prepared using a Ti/Cd constant ratio in the precursor solution. The films were sintered at six different Ts in the 450-550 °C range, in an open atmosphere. The structure of the films was characterized by X-ray diffraction and the PA was evaluated by the photobleaching of methylene blue in an aqueous solution using a UV-vis spectrometer. The relative intensity of the diffraction peaks associated with CdO and CdTiO₃, change with the Ts. The better photocatalytic activities were obtained for the films sintered at 490 °C and 550 °C. When the CdO was removed from the films by chemical etching the PA decreased, showing the importance of coupling both oxides.     

Au/Al2O3纳米复合薄膜的制备和表征

用溶胶-凝胶法制备了Au/Al₂O₃纳米复合薄膜。利用X-射线衍射、X-射线光电子能谱、原子力显微镜以及紫外-可见光谱对薄膜的微观结构、表面形貌及光学性能进行了表征,研究表明:Au/Al₂O₃纳米复合薄膜是由纳米微晶组成的颗粒膜, 复合薄膜均匀、致密、无裂纹,Au以纳米晶核形式镶嵌于Al₂O₃基体中,纳米Au晶核的粒径为23～26nm;复合薄膜在可见光区有较强的吸收,吸收峰位置与烧结温度有关,吸收强度随烧结温度和金添加量增大而增大。     

A sol-gel route for the development of rare-earth aluminum borate nanopowders and transparent thin films

A new sol-gel route was applied to obtain Y_0.9Er_0.1Al₃(BO₃)₄ crystalline powders and amorphous thin films by using Al(acac)₃, B(OPrⁱ)₃, Y(NO₃)₃·6H₂O, and Er(NO₃)₃·5H₂O as starting materials dissolved in propionic acid and ethyl alcohol mixtures. Our study shows that propionic acid acts as good chelant agent for yttrium and erbium ions while ethyl alcohol allows to dissolve Al(acac)₃. This process makes the resulting sols very stable to obtain homogeneous gels and transparent amorphous thin films. In addition, the propionic acid prevents the sol precipitation, making easy porous- and crack-free thin film depositions. Chemical reactions involved in the complexation were discussed. As-prepared powders and films are amorphous and present a good thermal stability due to their high glass transition (746 °C) and crystallization temperatures (830 °C). This new sol-gel route showed to be adequate to obtain dense and crack-free thin films free of organic and hydroxyl groups that can be considered as promising materials to be used in integrated optical systems.     

Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films

Al₂O₃ and TiO₂ thin films were deposited by atomic layer deposition at 80-250 °C on various polymeric substrates such as polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). The films were studied with FESEM, EDX, XRD, contact angle measurements and adhesion tests. The film growth rates on the thermoplastics were close to the corresponding growth rates on Si substrates. The adhesion of the films was good on PEEK and poor on PTFE. All coated surfaces showed lower water contact angles than the uncoated thermoplastics. Furthermore, the water contact angles on all TiO₂-coated surfaces decreased upon UV illumination, most efficiently with crystalline TiO₂ coatings.