Waveguides and gratings fabrication in zirconium-based organic/inorganic hybrids

Sol-gel derived poly(oxyethylene)/siloxane organic/inorganic di-ureasil hybrids containing different amounts of methacrylic acid (McOH, CH(2)=C(CH(3))COOH)) modified zirconium oxo-clusters (Zr-OMc) were processed as thin films deposited in glassy substrates via spin coating and as transparent and shape controlled monoliths. Channel monomode waveguides and diffraction gratings were UV patterned using the Talbot interferometer and the Lloyd mirror interferometer experimental setups. The time dependence of the diffraction gratings efficiency was studied for hybrids containing different amounts of Zr-OMc. Finally, the number of propagating modes and the refractive index gradient within the waveguide region, determined as a Gaussian section located below the patterned channel, was evaluated and modeled, a maximum index contrast of 2.43 X 10(-5) being estimated.

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

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

Crystallization study of molybdate phosphate glasses by thermal analysis

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

Low optical loss planar waveguides prepared in an organic-inorganic hybrid system

HfO2-(3-glycidoxipropil)trimethoxisilane (GPTS) planar waveguides were prepared by a sol-gel route. A stable sol of Hafnia nanocrystals was prepared and characterized by photon correlation spectroscopy and high resolution transmission electron microscopy. The suspension was incorporated in GPTS host and the resulting sol was deposited on borosilicate substrates by the spin coating technique. Optical properties such as refractive index, thickness, number of propagating modes, and attenuation coefficient were measured at 632.8, 543.5, and 1550 nm by the prism coupling technique as a function of the HfO2 content. (C) 2000 American Institute of Physics. [S0003-6951(00)03348-9].

Structure and crystallization of lanthanum fluorozirconate glasses

Glasses with compositions (1-x)ZrF4-xLnF(3), 0.2 less than or equal to x less than or equal to 0.4 and Ln = La or La, Eu have been synthesized and investigated using differential scanning calorimetry, X-ray diffraction, Raman scattering and Eu3+ optical spectroscopy. Single-phase polycrystalline lanthanum fluorozirconates with Zr/Ln ratio equal to 1, 2 and 3 have been investigated using the same techniques for comparison. The crystalline phases LnZrF(7), LnZr(2)F(11), LT-LnZr(3)F(15) (orthorhombic) and HT-LnZr(3)F(15) (trigonal) have been characterized in the recrystallized glasses and in samples spontaneously crystallized from the melt. Another phase has also been observed but remains undefined, the Raman scattering spectra of the vitreous samples are related to the vibration modes of [ZrF6] isolated octahedra, and of [ZrF7] and [ZrF8] structural units with bridging fluorine ions. The Eu3+ fluorescence data are related to a predominant local environment of the lanthanide ions in the glasses similar to that of the lanthanide in LnZrF(7).

Planar and UV written channel optical waveguides prepared with siloxane poly(oxyethylene)-zirconia organic-inorganic hybrids. Structure and optical properties

Organic-inorganic hybrids were prepared using ureapropyltriethoxysilane, methacryloxypropyltrimethoxysilane and acrylic acid modified zirconium(IV) n-propoxide precursors and were characterized by small angle X-ray scattering, X-ray diffraction and photoluminescence spectroscopy. The results indicate an effective interaction between the zirconium-based nanoparticles and the siliceous nanodomains that induces changes in the hybrids' emission features. Planar waveguides were obtained by spin-coating of the prepared sols on sodalime and silica substrates. Refractive index, thickness, number of propagating modes, and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm by the prism coupling technique. The synergism between the two hybrid precursors resulted in monomode planar waveguides with low losses in the infrared ( from 0.6-1.1 dB cm(-1)) which also support a number of propagating modes in the visible ( losses from 0.4-1.5 dB cm(-1)). Channel waveguides were also obtained by UV photopatterning using amplitude or phase masks and propagating modes were observed at 1550 nm.

Self-assembly of metallosupramolecules directed by (N-H)(2)center dot center dot center dot SCN-M (M = Co, Ni), C-H center dot center dot center dot pi and pi-pi synthons

This work deals with the synthesis, spectroscopic and structural investigation of pyrazolyl complexes of the type trans-[M(NCS)(2)(HPz)(4)] {M=Co (1), Ni (2); HPz=pyrazole}. Single crystal X-ray studies on 1 and 2 reveal the formation of similar supramolecular arrangements derived from self-assembly of monomers linked together through intermolecular N-H center dot center dot center dot SCN hydrogen bonds, C-H center dot center dot center dot pi interactions and pi-pi stacking. (c) 2005 Elsevier B.V. All rights reserved.

Crystallization kinetic of fluoro-zirconate glasses by non-isothermal analysis

Fluoride glasses have been extensively studied due to their high transparency in the infrared wavelength. The crystallization kinetics of these systems has been studied using DTA and DSC techniques. Most of the experimental data is frequently investigated in terms of the Johnson-Mehl-Avrami (JMA) model in order to obtain kinetic parameters.In this work, DSC technique has been used to study the crystallization of fluorozirconate glass under non-isothermal conditions. It was found that JMA model was not fit to be applied directly to these systems, therefore, the method proposed by Malek has been applied and the Sestak-Berggren (SB) model seems to be adequate to describe the crystallization process.

Crystallization of bothropstoxin II isolated from the venom of Bothrops jararacussu

A myotoxic phospholipase A(2), bothropstoxin II, which exhibits low hydrolytic activity, was crystallized and X-ray diffraction data were collected to a resolution of 2.2 Angstrom. Preliminary analysis reveals the presence of three molecules in the asymmetric unit. Copyright (C) 1996 Elsevier B.V. Ltd.

Purification, crystallization and preliminary X-ray diffraction analysis of carboxyhaemoglobin-II from the fish Piaractus mesopotamicus (pacu)

Carboxyhaemoglobin-II isolated from the pacu (Piaractus mesopotamicus) has been crystallized and X-ray diffraction data were collected to 2.0 Angstrom resolution using synchrotron radiation. Crystals were characterized as belonging to the space group I23; preliminary structural analysis reveals the presence of one dimer in the asymmetric unit.

Crystallization and preliminary X-ray diffraction analysis of prephenate dehydratase from Mycobacterium tuberculosis H37Rv

Tuberculosis remains the leading cause of mortality arising from a bacterial pathogen ( Mycobacterium tuberculosis). There is an urgent need for the development of new antimycobacterial agents. The aromatic amino-acid pathway is essential for the survival of this pathogen and represents a target for structure-based drug design. Accordingly, the M. tuberculosis prephenate dehydratase has been cloned, expressed, purified and crystallized by the hanging-drop vapour-diffusion method using PEG 400 as a precipitant. The crystal belongs to the orthorhombic space group I222 or I2(1)2(1)2(1), with unit-cell parameters a = 98.26, b = 133.22, c = 225.01 angstrom, and contains four molecules in the asymmetric unit. A complete data set was collected to 3.2 angstrom resolution using a synchrotron-radiation source.

Crystallization and preliminary X-ray diffraction analysis of XAC1151, a small heat-shock protein from Xanthomonas axonopodis pv. citri belonging to the alpha-crystallin family

The hspA gene (XAC1151) from Xanthomonas axonopodis pv. citri encodes a protein of 158 amino acids that belongs to the small heat-shock protein ( sHSP) family of proteins. These proteins function as molecular chaperones by preventing protein aggregation. The protein was crystallized using the sitting-drop vapour-diffusion method in the presence of ammonium phosphate. X-ray diffraction data were collected to 1.65 angstrom resolution using a synchrotron-radiation source. The crystal belongs to the rhombohedral space group R3, with unit-cell parameters a = b = 128.7, c = 55.3 angstrom. The crystal structure was solved by molecular-replacement methods. Structure refinement is in progress.