Effect of diphenyldiethoxysilane on the self-organized formation of nanocrystalline layered organosilicates in organic–inorganic hybrid films

Hybrid organic–inorganic films containing layered organosilicate nanocrystals have been obtained through self-organization from aqueous precursor sols containing 3-glycidoxypropyltrimethoxysilane. Diethoxydiphenylsilane has been added, in different amounts, to the precursor sol containing 3-glycidoxypropyltrimethoxysilane to prepare hybrid films with the ordered nanostructures. The effect of aging time of the precursor sol has been studied preparing different samples from sols aged up to 8 days; the formation of crystalline layered films has been observed in the samples obtained from sols of higher aging time. The hybrid films have been characterized by gracing incidence X-ray diffraction, Raman and Fourier transform infrared spectroscopy, transmission electron microscopy and UV–Vis spectroscopy. The change of the surface contact angle as a function of sol aging time and composition has been also measured. The capability of the films to be used in devices through lithographic techniques has been tested by writing the films with direct exposition to deep X-ray lithography and soft lithography with micromolds; patterns of different geometries with a thickness up to 100 μm have been obtained.     

Formation of hybrid nano-crystals in organic–inorganic films from a basic sol

Organic–inorganic films containing hybrid nanocrystals have been prepared by sol–gel processing in controlled conditions. We have systematically changed the temperature and the aging time of a precursor sol containing an organically modified alkoxide bearing an epoxy group, 3-glycidoxypropyltrimethoxysilane, to obtain a controlled crystallization of hybrid layered structures in hybrid films. The precursor sol has been aged at different temperatures, from 5 to 60 °C, and for 1, 2 or 3 days; the films have been deposited from the aged sol and immediately after characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. We have observed that the formation of the hybrid crystals can be obtained only when at least 50% of the epoxies are opened and a larger silica condensation is achieved. These conditions are reached after aging at 60 °C for 1 day, or at longer aging times when the sol is aged at lower temperatures. Transmission electron microscopy and optical polarized images have confirmed the formation of the hybrid crystals.     

Effect of Processing Parameters on the Optical Properties of TiO<Subscript>2</Subscript>/Ormosil Planar Waveguide

Hybrid TiO₂/ormosil waveguiding films have been prepared by the sol-gel method at low thermal treatment temperature of 150C. The influence of processing parameters including the molar ratios of titanium butoxide (Ti(OBu)₄)/3-glycidoxypropyltrimethoxysilane (GLYMO) and H₂O/Ti(OBu)₄ (expressed as R), especially aging of sol on the optical properties was investigated. The optical properties of films were measured with scanning electron microscope (SEM), UV/VIS/NIR spectrophotometer (UV-Vis), m-line and the scattering-detection method. The results indicate that the film thickness increases with the increase of sol aging time, but the variation of refractive index as a function of sol aging time depends on the relative ratios of GLYMO to Ti(OBu)₄. Higher transmittance and lower attenuation of the planar waveguide can be obtained in the sol with lower Ti(OBu)₄ contents and shorter aging time.     

Effect of amine catalysts on preparation of nanometric SiO<Subscript>2</Subscript> particles and antireflective films via sol–gel method

SiO₂ sols were prepared by hydrolysis and condensation reactions of tetraethyl orthosilicate through a one step acid or a two step acid + base catalysis process, in the presence of nitric acid and four different base catalyzers, namely trimethylamine, triethylamine, tripropylamine and tributylamine. Hydrolysis of TEOS was followed by FT-IR analyses. Particle size distributions of the sols were evaluated after predetermined durations in 1–22 days. Particle growth was seen to be faster in amine catalyzed systems than in one step acid catalyzed system. The highest rate of growth was in triethylamine catalyzed system. Glass substrates were dip coated with the prepared SiO₂ sols. Effect of sol aging duration on film thickness and on light transmittance properties of the films was investigated with respect to type of base catalyst. Thicknesses of the films which were measured to be in the range of 100–400 nm, were seen to increase with aging duration of the sols. Triethylamine catalyzed system presented the highest film thickness. Films obtained from one step acid catalyzed system presented an increase of 4.8%; whereas acid + base catalyzed films provided an increase in the light transmittance of 5.7% in the first 4 days of aging. Surfaces of films were examined by FESEM and AFM. The antireflective character of the films was verified by diffuse reflectance analyses.     

Formation of cerium titanate,CeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>, in sol–gel films studied by XRD and FAR infrared spectroscopy

The process of formation of cerium titanate films as a function of annealing temperature and composition has been studied by combining X-ray diffraction analysis and far infrared spectroscopy. The films have been prepared by a sol–gel synthesis using metal chlorides as precursors; the synthesis allows obtaining cerium titanate films upon annealing in air. A brannerite type, CeTi₂O₆, phase has been identified by X-ray diffraction and Rietveld analysis on thin films. CeTi₂O₆ is formed upon annealing at 700 °C and in a limited range of ceria-titania mixed compositions. The far infrared spectra are useful to observe the formation of crystalline phases at the beginning of the crystallization process at lower firing temperatures, when the XRD analysis is not enough sensitive.     

二氧化钛纳米晶薄膜的吸收光谱和激发发射光谱

由TiO₂反胶束溶胶制备一系列TiO₂纳米晶薄膜，对膜的吸收光谱和激发发射光谱研究表明制备的膜存在有二种模式的跃迁，直接跃迁和间接跃迁。由于厚膜中存在较强的表面相互作用，厚膜的直接跃迁禁带宽与薄膜相比发生了红移。在不同陈化时间，浸渍相同次数制得的膜具有相同的直接跃迁禁带宽。除浸渍一次的膜不存在间接跃迁外，所有的膜具有相同的间接跃迁禁带宽。所有的膜具有几乎相同的发射光谱模式。     

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.     

Preparation and photocatalytic activity of TiO<Subscript>2</Subscript> films with Ni nanoparticles

Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)₂ (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO₂ sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO₂ films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO₂ solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO₂ system revealed well-dispersed Ni nanoparticles supported on TiO₂ and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO₂ films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO₂.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Growth and characterization of (K<Subscript>0.5</Subscript> Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> thin films by a sol–gel method

(K_0.5 Na_0.5)NbO₃ (KNN) perovskite materials have been developed as a promising lead-free piezoelectric material for environmentally benign piezoelectric devices. KNN films with about 320 nm thickness were fabricated on Pt(111)/SiO₂/Si(100) substrates by a sol–gel method from stoichiometric and A-site ion excess precursor solutions. Two different annealing methods were also used to investigate the crystallographic evolution of the films. A layer-by-layer annealing process results in highly (001) oriented KNN from the annealing temperature of 550 °C, while the final annealing method leads to weaker crystalline peaks with a random orientation. The KNN films from the K and Na excess precursor solutions show similar crystallization behavior. However, the ferroelectric hysteresis loops of the films were greatly improved by compensating for an A-site vacancy. In particular, the KNN films from K-excess precursor solutions show better ferroelectric properties compared to the films prepared from Na excess solutions.     

Bismuth titanate thin films prepared by wet-chemical techniques: effect of sol ageing time

In this work, layered perovskite bismuth titanate (Bi₄Ti₃O₁₂) thin films were fabricated on α-alumina substrates by spin coating process. Precursor sol was prepared by sol–gel process from bismuth nitrate and titanium butoxide in concentrated acetic acid, with diethylamine as a stabilizer. Processes occurring in the precursor sol were followed in the ageing period of 20 days. Thin films prepared from the as-synthesized and aged sols are crack-free, with the thickness of ~1 μm, uniform surface texture and rounded grains having grain size in nanometer range. Sintering of thin films was performed at various temperatures, and sintered thin films exhibited dense structure, fully crystallized with typical Aurivillius phase and without any preferred orientation and impurity phase. The influence of ageing of the precursor sol on the microstructure of obtained thin films was also investigated. Direct relation between hydrodynamic diameter of precursor particles and the morphology and the grain size of the obtained films was observed.     

Preparation and characterization of CuAlO2 transparent thin films prepared by chemical solution deposition method

CuAlO₂ thin films were prepared on quartz glass and sapphire substrates by chemical solution deposition method using copper acetate monohydrate, aluminum nitrate nonahydrate and 2-methoxyethanol as starting precursor and solvent. The effects of annealing temperature on the structural, morphological, electrical and optical properties have been studied. Via the optimized annealing treatment condition, CuAlO₂ film annealed at 850 °C in nitrogen flow of 400sccm under atmosphere pressure exhibits the best performance with the lowest room temperature resistivity of 3.6 × 10² Ω cm and the highest optical transmission in the visible region (>70% at around 600 nm wavelength). CuAl₂O₄ and CuO phases, not CuAlO₂ phase are obtained when annealing temperature is lower than 850 °C. However, a further increase of annealing temperature weakens the crystallization quality and deteriorates the surface morphology of CuAlO₂ films as the annealing temperature exceeds 850 °C, leading to an increase in the resistivity and a decrease of the optical transmission in the visible region of CuAlO₂ films.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

A comparative studyof heat‐treated Ag:SiO2 nanocomposites synthesized by cosputtering and sol‐gel methods

In this work, we compared formation and properties of heat‐treated Ag nanoparticles in silica matrix synthesized by RF‐reactive magnetron cosputtering and sol–gel methods separately. The sol–gel and sputtered films were annealed at different temperatures in air and in a reduced environment, respectively. The optical UV‐visible spectrophotometry have shown that the absorption peak appears at 456 and 400 nm wavelength indicating formation of silver nanoparticles in SiO₂ matrix for both the sol–gel and sputtering methods at 100 and 800 °C, respectively. XPS measurements showed that the metallic Ag⁰ nanoparticles can be obtained from both the techniques at these temperatures. According to XPS and AFM analysis, by increasing annealing temperature, the concentration of the Ag nanoparticles on the surface decreased and the nanoparticles diffused into the substrate for the sol–gel films, while for the films deposited by cosputtering method, the Ag surface concentration increased by increasing the temperature. Based on AFM observations, the size of nanoparticles on the surface were obtained at about 25 and 55 nm for sputtered and sol–gel films, respectively, supporting our optical data analysis. In comparison, the sputtering technique can produce Ag metallic nanoparticles with a narrower particle size distribution relative to the sol–gel method. Copyright © 2008 John Wiley & Sons, Ltd.     

Tin Acetylacetonate as a Precursor for Producing Gas-Sensing SnO<Subscript>2</Subscript> Thin Films

To expand the range of precursors used in the sol–gel technology for applying nanostructured SnO₂ thin films promising as components of semiconductor chemical gas sensors, the efficiency of using tin acetylacetonate solutions with various precursor concentrations was demonstrated. It was determined that finely divided SnO₂ with a crystallite size of 3–4 nm (cassiterite) can be obtained by hydrolysis by atmospheric moisture in the course of solvent evaporation at room temperature. Using tin acetylacetonate solutions with various precursor concentrations for applying SnO₂ thin films by dip coating to the surface of rough ceramic Al₂O₃-based substrates with platinum interdigital electrodes and a microheater resulted in significant differences in microstructure, continuity, thickness, and porosity of the produced coatings. In a lower-concentration (0.13 mol/L) tin acetylacetonate solution, a multilayer dense continuous SnO₂ coating was applied, whereas in a higher-concentration (0.25 mol/L) solution, the formed layer comprised aggregated nanoparticles 30–60 nm in size and had much more defects and higher porosity. The sensitivity of the obtained thin-film nanostructures to the most practically important gaseous analytes: CO, H₂, CH₄, CO₂, and NO₂. The produced two-dimensional nanomaterials were shown to be promising for detecting carbon monoxide at 200–300°C in dry air.     

Aging and cold crystallization of melt‐extruded poly(trimethylene terephthalate) films

We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001     

Multifunctional performances of nanocomposite SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> doped cationic EBODAC film coated on natural cellulose matrix

Reverse micellar microemulsions were utilised to synthesise stable lead titanate colloids from typical sol–gel type molecular precursors. The particles of a few nanometres in diameter that formed by hydrolysis in the micelle cores demonstrated a nanocrystalline texture without the need for thermal treatment. In a chemical solution deposition routine based on the nanoparticle dispersions, ferroelectric PbTiO₃ thin films showing excellent remanent polarisation of more than 50 μC cm⁻² were derived. The electrical characteristics of the layers were correlated to their microstructure which was controlled by the precursor composition and the annealing conditions. A columnar morphology that was realised by spinning on coatings of up to 100 nm in individual thickness proved most favourable with respect to the ferroelectric performance of the films.     

甲胺铅碘前驱体薄膜放置过程中物质结构演变及对后续钙钛矿薄膜的影响

系统研究了甲胺铅碘(MAPbI_3)前驱体薄膜在室温大气中放置过程的物质结构变化过程,发现甲胺铅碘前驱体进一步生成了更多的MAPbI_3钙钛矿,大约220 min后MAPbI_3钙钛矿不再增加而且仍有前驱体。此外还分析了这种结构演变对后续钙钛矿薄膜热退火结果的影响,发现放置后的甲胺铅碘前驱体薄膜退火过程中的X射线衍射强度和紫外-可见吸收均比新制备的薄膜的低,而且通过原子力表面形貌图的对比发现,放置后的薄膜热退火后的薄膜晶体尺寸远小于新制备的甲胺铅碘前驱体薄膜热退火后的晶体尺寸,放置后的薄膜晶体尺寸约为0.2μm,新制备的薄膜晶体尺寸约为1.1μm。主要原因在于:甲胺铅碘前驱体薄膜由于在室温大气中放置过程中多生成了部分甲胺铅碘(MAPbI_3),因此晶体成核数量较多,晶粒数量增加,晶体存在较多缺陷,薄膜结晶度低,所以退火时X射线衍射强度和光谱强度较低,同时晶粒尺寸变小。研究为探讨甲胺铅碘钙钛矿生成机理提供了新的思路和方向,属于甲胺铅碘钙钛矿薄膜性质的基础性研究,对实际生产和工业应用有一定指导意义。     

Determination of optical constants of sol‐gel derived Zn0.9Mg0.1O films by spectroscopic ellipsometry with various models

The Zn_0.9Mg_0.1O thin films were prepared on Si (100) substrates by the sol‐gel method. The structural and the optical properties of Zn_0.9Mg_0.1O thin films, submitted to an annealing treatment in the 400–700 °C ranges, are studied by X‐ray diffraction (XRD) and ultraviolet (UV)‐visible spectroscopic ellipsometry (SE). The thickness, refractive index, and extinction coefficient of these films have been determined by analyzing the SE spectra using parameterized dispersion model. Moreover, we made a detailed comparison among various dispersion models and found that the Sellmeier model was superior to others in fitting the ellipsometric spectra in the transparent region. In the interband transition region, point‐by‐point fit was used. The spectral dependence of the refractive index and extinction coefficient was obtained in the photon energy range of 1.5–4.71 eV. The influence of annealing temperature on the refractive index, the extinction coefficient, and the optical bandgap energy was also discussed. We found that the refractive index and the extinction coefficient increase with increasing the annealing temperature, meaning the optical quality of Zn_0.9Mg_0.1O films is improved by annealing. Copyright © 2009 John Wiley & Sons, Ltd.     

SnO<Subscript>2</Subscript> thin films from an aqueous citrato peroxo Sn(IV) precursor

In this work, tin(II) oxalate was studied as a novel chloride-free starting material for the preparation of a stable Sn-containing precursor solution. This precursor was applied for the chemical solution deposition (CSD) of transparent conducting coatings of SnO₂ on Si/SiO₂ substrates. An influence of synthesis parameters, such as pH, complexing agent to metal ion ratio on the stability of the citrato peroxo Sn(IV) precursor has been investigated in this study. Insights into the precursor chemistry and its thermal decomposition based on TG-DSC analysis are also presented. The obtained SnO₂ films were characterized by high temperature X-ray diffraction (HT-XRD) and scanning electron microscopy (SEM) to evaluate phase purity and film thickness, respectively.