Electrical and Optical Properties of Conductive and Transparent ITO@PMMA Nanocomposites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of low-level laser therapy (685 nm) at different doses in osteogenic cell cultures

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Thermal evaporation furnace with improved configuration for growing nanostructured inorganic materials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Amorphous manganese polyphosphates: preparation, characterization and incorporation of azo dyes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of In concentration in the starting solution on the structural and electrical properties of ZnO films prepared by the pyrosol process at 450 degrees C

Undoped and indium-doped Zinc oxide (ZnO) solid films were deposited by the pyrosol process at 450 degrees C on glass substrates From solutions where In/Zn ratio was 2, 5, and 10 at.%. Electrical measurements performed at room temperature show that the addition of indium changes the resistance of the films. The resistivities of doped films are less than non-doped ZnO films by one to two orders of magnitude depending on the dopant concentration in the solution. Preferential orientation of the films with the c-axis perpendicular to the substrate was detected by X-ray diffraction and polarized extended X-ray absorption fine structures measurements at the Zn K edge. This orientation depends on the indium concentration in the starting solution. The most textured films were obtained for solutions where In/Zn ratio was 2 and 5 at.%. When In/Zn = 10 at.%, the films had a nearly random orientation of crystallites. Evidence of the incorporation of indium in the ZnO lattice was obtained from extended X-ray absorption fine structures at the In and Zn K edges. The structural analysis of the least resistive film (Zn/In = 5 at.%) shows that In substitutes Zn in the wurtzite structure. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Scandium fluorophosphate glasses: a structural approach

A systematic investigation on glass formation in the ternary system InF3-BaF2-[Sc(PO3)(3)](n) has been carried out. Scandium polyphosphate [Sc(PO3)(3)](n) has been used as a third component in order to investigate the possibilities of obtaining new stable glasses. The above long-chain polyphosphate has been prepared using a specially elaborated cryo-technique, which allowed the preparation of high-purity product. Stable ternary compositions have been obtained within the compositions range (in mol%): 5-75 InF3, 0-80% BaF2, 0-50% [Sc(PO3)(3)](n). Glasses were characterized by Differential Scanning Calorimetry, vibrational spectroscopy (Raman) and P-31 NMR. Structural features for the glass were put forward. Isolated P(O,F)4 groups or fluoroindated metaphosphate units could be identified depending on glass compositions. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

Morphological characterization of Langmuir-Blodgett films from polyaniline and a ruthenium complex (Rupy): influence of the relative concentration of Rupy

We report on the use of dynamic scale theory and fractal analyses in a study of the growth stages of Langmuir-Blodgett (LB) films of polyaniline and a neutral biphosphinic ruthenium complex, namely mer-[ RuCl3 (dppb)(py)] (dppb = 1,4-bis(diphenylphosphine) buthane, py = pyridine), Rupy. The LB films were deposited onto indium-tin-oxide substrates and characterized with atomic force microscopy. From the granular morphology exhibited by the films one could infer growth processes inside and outside the grains. Growth outside was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of about 2.7. As one would expect, inside the grains the morphology is close to a Euclidian surface with fractal dimension of about 2.

SrBi2Ta2O9 ferroelectric thick films prepared by electrophoretic deposition using aqueous suspension

SrBi2Ta2O9 ferroelectric thick films were prepared by electrophoretic deposition (EPD). For that, ceramic powders were prepared by chemical method in order to obtain compounds with chemical homogeneity. The polymeric precursor method was used for the synthesis of the SrBi2Ta2O9 powder. The crystallographic structure of the powder was examined by X-ray diffraction, and the surface area was determined by single point BET adsorption. The 0.03 vol.% suspension was formed by dispersing the powder in water using two different polymers as dispersants: an ester polyphosphate (C213) and an ammonium polyacrilate (Darvan 821-A). It was investigated the influence of the different dispersants in the surface properties of the powder by zeta potential measurements. The films were deposited on platinum-coated alumina and Pt/Ti/SiO2/Si substrates by a 4 mA constant current, for 10 min, using two parallel electrodes placed at a separation distance of 3 min in the suspension. Several cycles of deposition-drying of the deposit were carried out until reaching the desired thickness. After thermal treatment at temperatures ranging from 700 to 1000 degreesC, the films were characterized by X-ray diffraction and scanning electron microscopy for the microstructure observation. (C) 2003 Elsevier Ltd. All rights reserved.

Thermal characterization of bacterial cellulose-phosphate composite membranes

Cellulose-phosphate composite membranes have been prepared from bacterial cellulose membranes ( BC) and sodium polyphosphate solution. The structure and thermal behavior of the new composites were evaluated by X-ray diffraction (XRD), P-31-nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis (TMA). From XRD analyses the I alpha and I beta cellulose crystalline phases were identified together with crystalline sodium phosphate that covers the cellulose microfibrils as revealed by SEM. P-31 NMR spectra show peaks assigned to Q(0) and Q(1) phosphate structures to be compared to the Q(2) units that characterize the precursor polyphosphate. Glass transition temperature, T-g, obtained from TMA curves and thermal stability obtained from TG and DSC measurements, were observed to be dependent on the phosphate content.

Nanostructure and properties of ZnO films produced by the pyrosol process

Indium doped ZnO films were deposited by the pyrosol process on glass substrates at different temperatures from solutions containing In/Zn molar ratios up to 10%. The nanostructure of the films was investigated using grazing-incidence small angle X-ray scattering (GISAXS). The mass density was determined by X-ray reflectivity and the composition by X-ray photoelectron spectroscopy. The GISAXS measurements revealed an anisotropic pattern for films deposited at 573 and 623 K and a isotropic one for those deposited at higher temperatures. The anisotropic patterns indicate the presence of elongated nanopores with their long axes perpendicular to the film surface. In contrast, the isotropic nature of GISAXS patterns of films grown at high temperatures (673 and 723 K) suggests the presence of spherical voids. The pore size distribution function determined from the isotropic patterns indicates a multimodal size distribution. on the other hand, the measured mass density of the doped films with isotropic nanotexture is higher than that of the anisotropic films while the electric resistivity is significantly lower. This is in agreement with the detected strong reduction of the void density and specific surface area at approximately constant pore size.

Preparation of zinc sodium polyphosphates glasses from coacervates precursors. Characterisation of the obtained glasses, and their applications

A soft chemistry route is described to obtain glasses in the P2O5-Na2O-ZnO-H2O. It is based on the addition of zinc salts to coacervates prepared from sodium polyphosphate. The processing of these coacervates leads to polyphosphate glasses with the same properties as those of glasses prepared in the classical way. So far, little work has been implemented in this system using 'coacervate route'. However, it makes an attractive method for coating and joining processes on the industrial scale. As the anion associated to zinc may take part in the adhesion mechanism, coacervate formation has been studied using zinc chloride, nitrate and sulphate as starting materials. The physical properties of the glasses obtained by this method are reported and potential applications of zinc and silver coacervate are described. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

Preparation of SrBi2Ta2O9 ferroelectric thick films by electrophoretic deposition using aqueous suspensions

SrBi2Ta2O9 ferroelectric thick films were prepared by electrophoretic deposition (EPD). For that, ceramic powders were prepared by chemical method in order to obtain compounds with chemical homogeneity. The polymeric precursor method was used for the synthesis of the SrBi2Ta2O9 powder. The crystallographic structure of the powder was examined by X-ray diffraction, and the surface area was determined by single point BET adsorption. The 0.03 vol% suspension was formed by dispersing the powder in water using two different polymers as dispersants: an ester polyphosphate (C213) and an ammonium polyacrilate (Darvan 821-A). The influence of the different dispersants on the powder surface properties were investigated by zeta potential measurements. The films were deposited on platinum-coated alumina and Pt/Ti/SiO2/Si substrates by electrophoretic deposition using a 4 mA constant current, for 10 min, with two parallel electrodes placed at a separation distance of 3 min in the suspension. Several cycles of deposition-drying of the deposit was carried out until the desired thickness was obtained. After thermal treatment at temperatures ranging from 700 to 1000degreesC, the films were characterized by X-ray diffraction and scanning electron microscopy.

Enhanced Eu3+ Emission in Aqueous Phosphotungstate Colloidal Systems: Stabilization of Polyoxometalate Nanostructures

Luminescent Eu3+-containing polyphosphate tungstate aqueous colloidal systems were prgared and studied as a function of the relative polyphosphate tungstate content. In polyphosphate-rich solutions, Eu-H- ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu3+ ion and the 500 emission quantum efficiency is 0.22. Tungstatc addition leads to important modifications in neighboring Eu3+ leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show \V-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstatc relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu34- in polyoxometalate (P0M)-like sites by comparison with the well-known decatungstoeuropate [EuW10O36](9-) structure. These new aqueous colloids display surprisingly high 5llo emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu3+ first coordination shell.

Er(3+) doped phosphoniobate glasses and planar waveguides: structural and optical properties

Phosphoniobate glasses with composition (mol%) (100-x) NaPO(3)-xNb(2)O(5) ( x varying from 11 to 33) were prepared and characterized by means of thermal analysis, Fourier transform infrared spectroscopy, Raman scattering and (31)P nuclear magnetic resonance. The addition of Nb(2)O(5) to the polyphosphate base glass leads to depolymerization of the metaphosphate structure. Different colors were observed and assigned as indicating the presence of Nb(4+) ions, as confirmed by electron paramagnetic resonance measurements. The color was observed to depend on the glass composition and melting temperature as well. Er(3+) containing samples were also prepared. Strong emission in the 1550 nm region was observed. The Er(3+4)I(15/2) emission quantum efficiency was observed to be 90% and the quenching concentration was observed to be 1.1 mol%( 1.45 x 10(20) ions cm(-3)). Planar waveguides were prepared by Na(+)-K(+)-Ag(+) ion exchange with Er(3+) containing samples. Optical parameters of the waveguides were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique as a function of the ion exchange time and Ag(+) concentration. The optimized planar waveguides show a diffusion depth of 5.9 mu m and one propagating mode at 1550 nm.

CALCULATION of MAGNETODONOR STATES IN InP and POLARON EFFECTS

Far-infrared transitions in polar semiconductors are known to be affected by the presence of shallow donor impurities, external magnetic fields and the electron-LO-phonon interaction. We calculate the magnetodonor states in indium phosphide by a diagonalization procedure, and introduce the electron-phonon interaction by the Frohlich term. The main effects of this perturbation are calculated by a multi-level version of the Wigner-Brillouin theory. We determine the transition energies, from the ground state to excited states, and find good qualitative agreement with recently reported absorption-spectroscopy measurements in the 100-800 cm(-1) range, with applied magnetic fields up to 30 T. Our calculations suggest that experimental peak splittings in the 400-450 cm(-1) range are due to the electron-phonon interaction.