GeO2 based high k dielectric material synthesized by sol–gel process

Recently, there has been lot of research on new high dielectric constant (high k) materials for use in future generations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Keeping in view the properties required for the replacement of existing SiO₂ dielectrics, new high k dielectric material based on GeO₂ has been synthesized. Polycrystalline GeO₂ thin films have been deposited by simple, and cost effective sol–gel spin coating process. The obtained xerogel films of germanium oxide have been annealed at 400 °C, 600 °C and 800 °C for 3 h in argon atmosphere. Elemental composition, morphology, and phase analysis have been measured by employing X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques, respectively. The formation of the hexagonal GeO₂ phase at and above 400 °C has been reported. The composition of the annealed films have been measured and found to be 68 at.% of O, 32 at.% of Ge for GeO₂, which are close to the stoichiometry of the GeO₂.     

Dielectric properties of polystyrene–CCTO composite

The control of the dielectric properties of polymer composites is a relevant tool to synthesize a material to a specific industrial application. Polystyrene (PS) is a suitable host because it is readily available, and is easy to cast into desired shapes, maintaining the mechanical integrity of the matrix. CaCu₃Ti₄O₁₂ (CCTO) is a well-known high dielectric constant material, very useful for capacitors and memory devices. In this work, we studied the dielectric properties of the composite PS–CCTO, in the frequency range 10 Hz to 100 kHz, for CaCu₃Ti₄O₁₂ grains concentrations up to 64% by volume. Different mixture laws were used to fit the data: Hanai, Wiener, Maxwell–Wagner, Kraszewsky, Looyenga and Generalized Looyenga. The last one presents the best results. The calculated exponent of this law was then correlated with the shape particles observed by scanning electron microscopy. Finally, using Generalized Looyenga law, we can carefully select the adequate CCTO concentration in order to tailor the desired behavior, producing interesting composites for potential applications.     

Growth of pure ZnO thin films prepared by chemical spray pyrolysis on silicon

Structural, morphological, optical and electrical properties of ZnO thin films prepared by chemical spray pyrolysis from zinc acetate (Zn(CH₃COO)₂ 2H₂O) aqueous solutions, on polished Si(1 0 0), and fused silica substrates for optical characterization, have been studied in terms of deposition time and substrate temperature. The growth of the films present three regimes depending on the substrate temperature, with increasing, constant and decreasing growth rates at lower, middle, and higher-temperature ranges, respectively. Growth rate higher than 15 nm min⁻¹ can be achieved at T_s=543 K. ZnO film morphological and electrical properties have been related to these growth regimes. The films have been characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.     

Characterization of B2O3 and/or WO3 containing tellurite glasses

Characterization of B₂O₃ and/or WO₃ containing tellurite glasses was realized in the 0.80TeO₂–(0.20 ? x)WO₃ ? xB₂O₃ system (0 ≤ x ≤ 0.20 in molar ratio) by using differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry techniques. Glasses were prepared with a conventional melt-quenching technique at 750 °C. To recognize the thermal behavior of the glasses, glass transition and crystallization temperatures, glass stability value, glass transition activation energy, fragility parameter were calculated from the thermal analyses. Density, molar volume, oxygen molar volume and oxygen packing density values were determined to investigate the physical properties of glasses. Fourier transform infrared spectra were interpreted in terms of the structural transformations on the glass network, according to the changing B₂O₃ and/or WO₃ content. Crystallization behavior of the glasses was investigated by in situ X-ray diffraction measurements and microstructural characterization was realized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.     

Microwave preparation,structure and electrical properties of calcium–sodium–phosphate biosystem

The hydroxyapatite biomaterial (Ca₁₀(PO₄)₆(OH)₂ – HAP) is the main mineral constituent of teeth and bones, with excellent biocompatibility with hard and muscle tissues. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing them with a suitable binder. In this study, a microwave process was used to produce hydroxyapatite using the starting materials CaCl₂ and Na₂HPO₄ with previous precipitation. The mixture was exposed to microwave radiation for 5, 10, 15 and 20 min through domestic microwave ovens with an output power of 1 kW and frequency oscillation of 2.45 GHz. The samples were analyzed by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, dc conductivity and impedance spectroscopy. X-ray powder diffraction revealed the formation of HAP after 5 min of exposure. The presence of a low crystallinity state and the transition, with the rise of radiation exposure time, to a crystalline phase was related to the Ca/P mass and Ca/P atomic ratio. The presence of this low crystalline phase, detected by X-ray powder diffraction and scanning electron microscopy, seems to have a direct influence on electrical and dielectrical characteristics.     

High-yield synthesis of single-crystal short Eu2O3 nanorods through a facile sol–gel template approach

High-yield Eu₂O₃ short nanorods have been prepared by a facile sol-gel method with polystyrene/polyelectrolyte (PS/PE) microreactor as template in an aqueous solution of europium nitrate in the presence of ammonia and urea. The properties of Eu₂O₃ nanorods were characterized by powder X-ray diffraction, thermogravimetric analysis, transmission electron microscopy (TEM), high-resolution transmission electron microscopy, field emission scanning electron microscopy (FESEM), and photoluminescence spectroscopy. The particle sizes measured from TEM and FESEM are about 200 nm×500 nm (W×L). A possible mechanism for the formation of such high-yield oxide nanorods is discussed.     

Effects of substrate orientation on aluminum grown on MgAl2O4 spinel using molecular beam epitaxy

Al thin films have been grown on single-crystal MgAl₂O₄ spinel substrates using solid source molecular beam epitaxy. The structural properties of Al layers were systematically investigated as a function of substrate orientation. X-ray diffraction reveals that Al layers are coherently grown on both (0 0 1)- and (1 1 1)-oriented spinel substrates. However, scanning electron microscopy and atomic force microscopy show that Al layers on (0 0 1) spinel substrates display smoother surface morphology than those grown on (1 1 1) spinel substrates. Additionally, electron backscatter diffraction and transmission electron microscopy demonstrate the presence of a high density of twin domain structures in Al thin films grown on (1 1 1) spinel substrates.     

Synthesis of aligned ripple-like and helical structure silica fibres

Highly aligned ripple-like silica fibres, as well as helical structure fibres have been synthesized by a chemical vapor deposition technique. The as-grown product was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and selected-area electron diffraction. The results showed that the fibres were amorphous in nature with average diameters of 800 nm and lengths of several hundred micrometers. The formation of the fibres could be explained by the vapor–solid (VS) mechanism and the helical structure might be formed by a perturbation during the growth of the ripple-like fibres. The photoluminescence (PL) spectrum of the silica fibres showed two strong blue emission peaks at 450 nm (2.75 eV) and 415 nm (2.99 eV) under excitation at 260 nm.     

Preparation and the third-order optical nonlinearities of the sodium borosilicate glass doped with Cu7.2S4 quantum dots

The sodium borosilicate glass doped with Cu_7.2S₄ quantum dots was prepared by using both sol–gel and atmosphere control methods. The formation mechanism and the microstructure of the glass were examined using differential thermal analysis and thermal gravimeter (TG-DTA), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectra (EDX), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The results revealed that Cu_7.2S₄ quantum dots in orthorhombic crystal system had formed in the glass, and the size ranged from 9 nm to 21 nm. In addition, Z-scan technique was used to measure the third-order optical nonlinearities of the glass. The results indicated that the third-order optical nonlinear refractive index γ, the absorption coefficient β, and the susceptibility χ⁽³⁾ of the glass were 1.11 × 10^? 15 m²/W, 8.91 × 10^? 9 m/W, and 6.91 × 10^? 10 esu, respectively.     

Electrodeposited and selenized CIGS thin films for solar cells

Cu(In,Ga)Se₂ polycrystalline thin films were deposited adopting the potentiostatic electrochemical method on Mo/soda lime glass substrate. All the as-deposited Cu(In,Ga)Se₂ thin films were annealed in a selenium atmosphere at 550 °C for 1 h to improve the film crystalline properties. The selenized CIGS thin films were characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results indicate Cu(In,Ga)Se₂ thin films have single chalcopyrite structure and the grain size varies from 0.8 to 2.5 μm.     

Synthesis,characterization and application of magnetic-zirconia nanocomposites

In the present study, a magnetic-zirconia nanocomposite was successfully synthesized by a single-step co-precipitation method. The as-prepared nanocomposite was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and nitrogen sorption measurements. The ultimate material was found to be Fe₃O₄–ZrO₂ nanoparticles with average diameter of 80 nm, high surface area up to 166 m²/g, and strong magnetic property. The application of this new nanocomposite was herein demonstrated by the adsorption of ethyl methylphosphonic acid, a degradation product of nerve agent in water, followed by mass spectrometry detection. Excellent adsorption could be observed, indicating the as-synthesized material was effective to remove phosphonic acid compound from water. Apart from adsorption, the Fe₃O₄–ZrO₂ nanocomposite is promising in various applications such as catalysis and bioseparation.     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

The effect of cooling rate during hydrothermal synthesis of ZnO nanorods

The hydrothermal method was employed in order to obtain zinc oxide nanorods directly on Si/SiO₂/Ti/Zn substrates forming brush-like layers. In the final stages of synthesis, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction results showed that all the nanostructures grew [0 0 0 1] oriented perpendicular to the substrate. The influence of the cooling process over the morphology and dimensions of the nanorods was studied by scanning electron microscopy. High-resolution transmission electron microscopy images of the quenched samples showed that the zinc oxide (ZnO) crystal surfaces exhibit a thin-layered coating surrounding the crystal with a high degree of defects, as confirmed by Raman spectroscopy results. Photodetectors made from these samples exhibited enhanced UV photoresponses when compared to the ones based on naturally cooled nanorods.     

Preparation and characterization of amorphous silica nanowires from natural chrysotile

By chemical dispersing and acid leaching, silica nanowires have been prepared from the natural mineral, chrysotile. X-ray fluorescence analysis (XRF), thermogravimetric analysis and differential thermogravimetric analysis (TGA–DTA), powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the silica nanowires. The results indicate that the chemical composition of the silica nanowires is SiO_1.8 · 0.6H₂O, and although the silica is amorphous, its structure is regular to some extent. The structural unit of the silica nanowires is the [SiO₄] tetrahedron and six-member silicon–oxygen ring with the tetrahedral positioned alternately up and down in the six-member ring. The silica nanowires are well-dispersed and have cylindrical morphology and smooth surface, with lengths over 10 μm and diameters of 30–60 nm.     

Synthesis and luminescent properties of novel RENbO4:Ln3+ (RE = Y, Gd, Lu; Ln = Eu, Tb) micro-crystalline phosphors

Using rare earth coordination polymers with aromatic carboxylic acids as the precursors of rare earth oxide components, with polyethylene glycol (PEG) as the dispersing media, micro-crystalline phosphors RENbO₄:Ln³⁺ (RE = Y, Gd, Lu; Ln = Eu, Tb) have been synthesized by an in situ co-precipitation method. Both X-ray diffraction and scanning electron microscopy have shown that the resultant samples present are crystalline with ‘rice glue ball’ micro-morphology and crystalline grain sizes in the range of 1–2 μm. The luminescent properties of these phosphors have been studied, which show that the best photoluminescent performance is achieved for GdNbO₄:Tb³⁺ or Eu³⁺. This was because Gd³⁺ plays an important role to enhance the luminescence of Tb³⁺ or Eu³⁺ in an energy transfer process. In addition, the influence of the doping concentration on the fluorescence behaviors has been examined. With increase of the doping concentration from 1 mol% to 5 mol%, both the red emission intensity of Eu³⁺ and the green emission intensity of Tb³⁺ increase.     

Crystallization of amorphous Al2O3–SiO2 precursors doped with nickel

The crystallization of amorphous diphasic Al₂O₃–SiO₂ precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al₂O₃ preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol⁻¹ for crystallization of Ni-containing γ-Al₂O₃ was obtained in non-isothermal conditions. Ni-incorporated γ-Al₂O₃ transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl₂O₄, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system.     

Dielectric,morphological and structural properties of lithium ferrite powders prepared by solid state method

Lithium ferrite (LiFe₅O₈) is one of the most known cubic ferrites which belong to the group of soft ferrite materials with high Curie temperature, presenting a square hysteresis loop, and high magnetization. It has attracted special attention due to its numerous technological applications in microwave devices, magnetic recording, transformer cores, rod antennas and possible applications in biomedics. It is also a promising candidate for cathode materials in rechargeable lithium batteries as well as low cost substitutes to garnet materials in microwave frequency applications.In the present work, amorphous Li₂O–Fe₂O₃ powders were prepared via wet ball milling method. The as-prepared powders were heat-treated at temperatures between 400 and 1400 °C and their structure analyzed by X-ray diffraction and Raman spectroscopy. The morphology was observed by scanning electron microscopy. Electrical and dielectric properties, in the frequency range between 100 and 2 MHz and temperatures between 200 and 360 K, were performed, and the results related with the structure and morphological characteristics.     

Hydrothermal synthesis and characterization of VO2 (B) nanorods array

Highly ordered nanorods array of B phase vanadium dioxide was firstly synthesized with n-butanol as the reducing agent via a simple hydrothermal method without using template. The samples have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The size of VO₂ (B) nanorods has the dimension of 50–100 nm in diameter and about 1–5 μm in length. The samples were measured as electrode materials by charge–discharge technique and the VO₂ (B) nanorods array demonstrated a high specific capacity of 520 mAh/g at 0.2 C. The influence of reaction temperature on fabricating nanorods array has been studied. The possible growth mechanisms of formation of nanorods and assembly of array were discussed.     

Bulk-quantity SnO2 nanorods synthesized from simple calcining process based on annealing precursor powders

Tin dioxide (SnO₂) nanorods have been successfully synthesized in bulk quantity by a calcining process based on annealing precursor powders in which sodium chloride, sodium carbonate, and stannic chloride were homogeneously mixed. Transmission electron microscopy shows that the as-prepared nanorods are structurally perfect and uniform, with widths of 10–25 nm, and lengths of several hundreds nanometers to a few micrometers. X-ray diffraction and energy-dispersive X-ray spectroscopy analysis indicate that the as-prepared nanorods have the same crystal structure and chemical composition found in the tetragonal rutile form of SnO₂. Selected area electron diffraction and high-resolution transmission electron microscopy reveal that the as-prepared nanorods grow along the [1 1 0] crystal direction. We found that the calcined temperature has a strong influence on the size and morphology of SnO₂ nanorods. The growth process of SnO₂ nanorods is suggested to follow an Ostwald ripening mechanism. Our findings indicate that other nanorods or nanowires may be manipulated by using this technique, and might provide insight into the new opportunities to control materials fabrication.     

Crystallization behavior of Dy3+-doped selenide glasses

Rare earth (RE)-doped chalcogenide glasses are an important promising material for active photonic devices, including mid-infrared (mid-IR) fiber lasers and amplifiers. Here we report on dysprosium ion (Dy³⁺)-doped GeAsGaSe chalcogenide glasses based on 10 atomic (at.) % Ga. A series of Dy³⁺-doped GeAsGaSe glasses, with increasing levels of Dy³⁺ dopant from 0 ppm to 2000 ppm added to the Ge_16.5As₉Ga₁₀Se_64.5 (at. %) base glass, is synthesized and characterized using: Fourier transform infrared spectrometry; X-ray diffraction (XRD); imaging and analysis using a high resolution transmission electron microscope, with selected area electron diffraction (HRTEM-SAED), and energy dispersive X-ray spectroscopy (HRTEM-EDX) and an environmental scanning electron microscope with energy dispersive X-ray spectroscopy (ESEM-EDX) and with secondary electron mapping. At the higher levels of Dy³⁺ doping, the glasses exhibit bulk crystallization; XRD, HRTEM-EDX and ESEM-EDX indicate the crystals are predominantly a modified, face centered cubic α-Ga₂Se₃, with some substitution of Ge. In addition, features on the bulk glass surface are shown to comprise Dy³⁺, sometimes accompanied by Si and [O] which, it is suggested, are due to contamination from the silica glass melting ampoule.