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Hexagonal Structure (hexagonal + structure)
Selected AbstractsSynthesis and properties of ,-Fe2O3 nanorodsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2010R. Ramesh Abstract We report synthesis of ,-Fe2O3 (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined ,-Fe2O3 nanorods were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the ,-Fe2O3 nanorods were hexagonal structure. The nanorods have diameter of 30-50 nm and length of 120-150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, optical and photoconductive properties of electron beam evaporated CdSxSe1-x filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2010K. Sivaramamoorthy Abstract CdSxSe1-x films were deposited by the electron beam evaporation technique on glass substrates at different temperatures in the range 30 , 300 °C using the laboratory synthesized powders of different composition. The films exhibited hexagonal structure and the lattice parameters shifted from CdSe to CdS side as the composition changed from CdSe to CdS side. The bandgap of the films increased from 1.68 to 2.41 eV as the concentration of CdS increased. The root-mean-roughness (RMS) values are 3.4, 2.6, 1.2 and 0.6 nm as the composition of the films shifted towards CdS side. The conductivity varies from 30 ,cm -1 to 480 ,cm -1 as the ,x' value increases from 0 to 1. The films exhibited photosensitivity. The PL spectrum shifts towards lower energies with decreasing x, due to the decrease of the fundamental gap with Se composition. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solvothermal production of CdS nanorods using polyvinylpyrrolidone as a templateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2009Titipun Thongtem Abstract CdS nanorods were solvothermally produced using Cd(NO3)2 and S powder in ethylenediamine containing different amounts of polyvinylpyrrolidone (PVP). The phase with hexagonal structure was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their SAED patterns were in accordance with those of the simulations. Scanning and transmission electron microscopies (SEM and TEM) revealed the presence of CdS nanorods with their lengths influenced by different amounts of PVP. The nanorods were also characterized using high resolution TEM (HRTEM). They grew in the [001] direction normal to the (002) parallel crystallographic planes composing the nanorods. Raman spectra showed the 1LO (first harmonic) and 2LO (second harmonic) modes at the same wavenumbers although the products were produced under different conditions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of FexMn1-xIn2Se4 (0 , x , 1) single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005G. Attolini Abstract Single crystals of Mn1-xFexIn2Se4 with 0 , x , 1.0 were grown by chemical vapor transport technique using I2 as transporting agent. The resulting crystals appeared as brilliant black plates. X-ray powder diffraction data could be indexed following the hexagonal structure with space group Rm for the low Fe concentration samples, while the high concentration sample is associated to the space group P63mc. Both polytypes have similar parameters, however the c parameter reduces as the Fe concentration increases, therefore the number of anion slabs decreases. The characterization of the crystals was based on morphological observations and optical absorption as a function of temperature. The obtained energy gap for the samples at different Fe concentrations suggested that they behave as direct energy gap semiconductors. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanostructured copolymer gels for dsDNA separation by CEELECTROPHORESIS, Issue 23 2008Fen Wan Abstract Pluronics are triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) that are able to form many different ordered nanostructures at appropriate polymer concentrations and temperatures in selective solvents. These nanostructured "gels" showed desirable criteria when used as DNA separation media, especially in microchip electrophoresis, including dynamic coating and viscosity switching. A ternary system of F127 (E99P69E99)/TBE buffer/1-butanol was selected as a model system to test the sieving performance of different nanostructures in separating dsDNA by CE. The nanostructures and their lattice constants were determined by small-angle X-ray scattering. Viscosity measurements showed the sol,gel transition phenomena. In addition to the cubic structure, successful electrophoretic separation of dsDNA in 2-D hexagonally packed cylinders was achieved. Results showed that without further optimization, ,X174 DNA,Hae III digest was well separated within 15,min in a 7-cm separation channel, by using F127/TBE/1-butanol gel with a 2-D hexagonal structure. A mechanism for DNA separations by those gels with both hydrophilic and hydrophobic domains is discussed. [source] Monomolecular-Layer Ba5Ta4O15 Nanosheets: Synthesis and Investigation of Photocatalytic Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2006T.-G. Xu Abstract Monomolecular-layer perovskite Ba5Ta4O15 nanosheets with hexagonal structure have been synthesized by a hydrothermal method. The thickness of the nanosheets is about 1.1,nm, which corresponds to a monolayer of Ba5Ta4O15 molecules, with the lateral size ranging from 50,to 200,nm. The optimal conditions for the formation of the nanosheets are maintaining the reactants above 270,°C for 24,h. A dissolution,recrystallization mechanism is suggested based on observations of the factors that influence nanosheet formation, such as reaction time, temperature, and basicity. Formation of Ba5Ta4O15 nanosheets takes precedence over other nanostructures under high concentrations of OH, because the hindering effect of OH, ions on the c -axis growth is strong. Thus, the extended growth rate of polyhedrons on one monolayer is much faster than the superposition rate of the monolayer, and the crystal grows more easily along the a - and b -planes. The Ba5Ta4O15 nanosheets show a high photocatalytic activity in the degradation of Rhodamine B and gaseous formaldehyde. The layered perovskite probably affects the photocatalytic activity by promoting the charge separation and delocalization of photogenerated electrons and holes. [source] Hexagonal and cubic TiOF2JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2010Samuel Shian The chemical, electrochemical, optical and electro-optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2 possesses a simple cubic structure (space group Pmm) at room temperature. Three-dimensional nanostructured assemblies of polycrystalline TiOF2 have recently been synthesized via chemical conversion of intricate SiO2 structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2 product formed by such reaction at 623,K. Unlike prior reports, this TiOF2 product possessed a hexagonal structure (space group Rc) at room temperature. Upon heating through 333,338 K, the hexagonal TiOF2 polymorph converted into cubic (Pmm) TiOF2. Differential scanning calorimetry and X-ray diffraction analyses have been used to evaluate this thermally induced phase transformation. [source] Self-assembled structures of hydrophobins HFBI and HFBIIJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Serimaa Ritva Hydrophobins are small proteins that function in the growth and development of fungi. The structures of class II hydrophobins HFBI and HFBII from Trichoderma reesei were studied using grazing incidence X-ray diffraction. HFBI was weakly ordered but HFBII formed a highly crystalline coating on water surface. Change from monoclinic to hexagonal structure was observed as the sample dried. The three-dimensional structures differed from the oblique two-dimensional structures observed in Langmuir-Blodgett monolayers of both HFBI and HFBII by atomic force microscopy. [source] Formation process of three-dimensional arrays from silica spheresAICHE JOURNAL, Issue 5 2003Keiji Ishikawa Elucidating the formation process of 3-D arrays from submicrometer-sized particles is a key to creating an optimal fabrication process of photonic crystals. In this research, the spontaneous sedimentation of silica spheres is imaged by in situ confocal laser scanning microscopy, and the dynamics is studied. When the pH is 7.0 and 10, the rate of the formation process of a hexagonal structure is attributed to the transport of spheres in the early stage of precipitation, and can be reproduced by a simple equation for Langmuir-type adsorption, ignoring the desorption part. In a later stage, however, the rate becomes smaller. In the first layer, even after drying, the nearest two spheres are separated, while maintaining a hexagonal structure. From the results, the formation process of three-dimensional arrays from silica spheres is illustrated. [source] Developing a hybrid emulsion polymerization system to synthesize Fe3O4/polystyrene latexes with narrow size distribution and high magnetite contentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Longlan Cui Abstract A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)-droplets with a diameter of 100,200 nm and styrene (St)-droplets with a diameter of 3,4 ,m, was obtained by mixing Mag-miniemulsion and St-macroemulsion. With extremely low surfactants concentration (,critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag-droplets, as the result of smaller droplet size and larger surface ratio. Both water-soluble potassium persulfate (KPS) and oil-soluble 2,2,-azobis(2-isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60,200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well-ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as-synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag-miniemulsion and St-macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285,5295, 2007 [source] Influence of Sn doping upon the phase change characteristics of Ge2Sb2Te5PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2004K. Wang Abstract The influence of Sn doping upon the phase change characteristics of Ge2Sb2Te5 alloys has been investigated using four-point-probe electrical resistance measurements, grazing incidence X-ray diffraction (XRD), X-ray reflectometry (XRR) and variable incident angle spectroscopic ellipsometry (VASE), a static tester and atomic force microscopy (AFM). For a Ge2Sb2Te5 alloy doped with 4% Sn, two transition temperatures are observed in the temperature dependent sheet resistance measurements at 125 °C and 250 °C, respectively. The evolution of structures upon annealing, investigated by XRD, reveals that the first transition is caused by the crystallization of the amorphous film to a NaCl-type structure, while the second transition is related to the transition to a hexagonal structure. The density values of 6.02 ± 0.05 g cm,3, 6.38 ± 0.05 gcm,3 and 6.42 ± 0.05 gcm,3 are measured by XRR for the film in the amorphous, NaCl-type and hexagonal structure, respectively. Ultra-fast crystallization, which is correlated with a single NaCl-structure phase and the reduced activation barrier, is demonstrated. Sufficient optical contrast is exhibited and can be correlated with the density change upon crystallization. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The influence of mechanical alloying on the structural and physical properties of YNi4B compoundPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003M. Timko Abstract We have investigated the influence of mechanical milling on structural changes, magnetic and superconducting properties of YNi4B compound. This compound crystallizes in a hexagonal structure with the P6/mmm space group. Magnetic measurements have shown that originally prepared sample exhibits superconducting behaviour below 12 K and above this temperature the sample is paramagnetic. The great decrease of intensity and broadening of diffraction lines have been detected after milling as a consequence of sample amorphisation. [source] Magnetic viscosity and activation volume in chromium substituted Pb,M hexaferritePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005J. C. Faloh-Gandarilla Abstract PbFe11CrO19 polycrystalline samples were prepared by the chemical coprecipitation method. X-ray diffraction and Mössbauer spectroscopy confirm the formation of the M-type hexagonal structure. Time dependence of the magnetization was recorded on the demagnetization curve of the hysteresis loop. It is well described by a simple logarithmic law but also non-logarithmic behavior was detected. A two-peak dependence of the viscosity coefficient S with the applied field was encountered. Considering reversible susceptibility measurements and a M(H) curve at constant dM/dt in the irreversible susceptibility determination, the calculated activation volume as a function of the applied field shows two well defined zones. The zones observed in the activation volumes are related to the two local maxima that the total susceptibility exhibits. It points to the fact that the viscosity study is sensible enough to characterize this system, encountering two apparent activation volumes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of lattice-translocation disorder in the layered hexagonal structure of carboxysome shell protein CsoS1CACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Yingssu Tsai Lattice-translocation or crystal order,disorder phenomena occur when some layers or groups of molecules in a crystal are randomly displaced relative to other groups of molecules by a discrete set of vectors. In previous work, the effects of lattice translocation on diffraction intensities have been corrected by considering that the observed intensities are the product of the intensities from an ideal crystal (lacking disorder) multiplied by the squared magnitude of the Fourier transform of the set of translocation vectors. Here, the structure determination is presented of carboxysome protein CsoS1C from Halothiobacillius neapolitanus in a crystal exhibiting a lattice translocation with unique features. The diffraction data are fully accounted for by a crystal unit cell composed of two layers of cyclic protein hexamers. The first layer is fully ordered (i.e. has one fixed position), while the second layer randomly takes one of three alternative positions whose displacements are related to each other by threefold symmetry. Remarkably, the highest symmetry present in the crystal is P3, yet the intensity data (and the Patterson map) obey 6/m instead of symmetry; the intensities exceed the symmetry expected from combining the crystal space group with an inversion center. The origin of this rare phenomenon, known as symmetry enhancement, is discussed and shown to be possible even for a perfectly ordered crystal. The lattice-translocation treatment described here may be useful in analyzing other cases of disorder in which layers or groups of molecules are shifted in multiple symmetry-related directions. [source] Structure of d(TGCGCG)·d(CGCGCA) in two crystal forms: effect of sequence and crystal packing in Z-DNAACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2005S. Thiyagarajan The sequence d(TGCGCG)·d(CGCGCA) crystallized in two crystal forms, orthorhombic and hexagonal, in the presence of cobalt hexammine chloride, a known inducer of the left-handed Z-form of DNA. The crystal structures have been solved and refined at 1.71,Å resolution in space group P212121 and 2.0,Å resolution in space group P65. The orthorhombic structure contains one Z-DNA hexamer duplex, while the hexagonal structure contains two hexamer duplexes in the structure. Of the latter, one is situated on a crystallographic sixfold screw axis, leading to disorder. This paper reports the effects of sequence and crystal packing on the structure of Z-type DNA. The structures lend additional support to the authors' earlier conclusion that a stretch of four C·G base pairs is sufficient to nucleate and define the regular model of the left-handed helix based on the structure of d(CGCGCG)2. [source] Synthesis and Characterization of Novel Super Microporous Tin-doped Zirconium OxideCHINESE JOURNAL OF CHEMISTRY, Issue 12 2005Yan Kong Abstract The super microporous tin-doped zirconium oxides were successfully synthesized by sol-gel method using zirconyl chloride as Zr source, tin chloride as Sn source and cetyltrimethylammonium bromide (CTMAB) as template under hydrothermal or refluxing conditions. The structures of the resultant materials were characterized by XRD, BET, FTIR, TG-DTA, XRF and HRTEM techniques. Experimental results indicated that the framework of the samples is typically ordered hexagonal structure. The surface area and pore volume of the materials prepared by refluxing method were larger than by hydrothermal method, but the ordering of pore distributions is lower. The thermal stability of the samples was relatively high (>773 K) and decreased with the increment of tin content. [source] Enhancement of Light Extraction Through the Wave-Guiding Effect of ZnO Sub-microrods in InGaN Blue Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Ki Seok Kim Abstract The improvement of the light extraction efficiency (LEE) of a conventional InGaN blue light-emitting diode (LED) by the incorporation of one-dimensional ZnO sub-microrods is reported. The LEE is improved by 31% through the wave-guiding effect of ZnO sub-microrods compared to LEDs without the sub-microrods. Different types of ZnO microrods/sub-microrods are produced using a simple non-catalytic wet chemical growth method at a low temperature (90,°C) on an indium-tin-oxide (ITO) top contact layer with no seed layer. The crystal morphologies of needle-like or flat-top hexagonal structures, and the ZnO microrods/sub-microrod density and size are easily modified by controlling the pH value and growth time. The wave-guiding phenomenon within the ZnO rods is observed using confocal scanning electroluminescence microscopy and micro-electroluminescence spectra. [source] Hydrogel Patterning: (Swelling-Induced Surface Patterns in Hydrogels with Gradient Crosslinking Density) Adv.ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Funct. In this paper by M. Guvendiren et al, a simple and robust method is used to generate a range of osmotically-driven surface patterns in hydrogels, including random, lamellar, peanut, and hexagonal structures. The patterns are fabricated by exposing a photocurable formulation to light while open to air and then swelling, using oxygen inhibition of the radical polymerization at the surface to create a gradient of crosslinking with depth. [source] Swelling-Induced Surface Patterns in Hydrogels with Gradient Crosslinking DensityADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Murat Guvendiren Abstract Hydrogels with controlled surface patterns are useful for a range of applications, including in microdevices, sensors, coatings, and adhesives. In this work, a simple and robust method to generate a wide range of osmotically driven surface patterns, including random, lamellar, peanut, and hexagonal structures is developed. This method does not require the use of organic solvents for swelling, pre-patterning of the film surface, or coating of a second layer on the gel. The patterns are fabricated by exposing a photocurable formulation to light while open to air and then swelling, using oxygen inhibition of the radical polymerization at the surface to create a gradient of crosslinking with depth, which was confirmed by measuring the double bond conversion at the surface, surface mechanics, and molecule diffusion into the network. The modulus gradient, and hence osmotic pressure, is controlled by the crosslinker concentration, and the characteristic size of the patterns is determined by the initial film thickness. The patterns are stable in both swollen and dry states, creating a versatile approach that is useful for diverse polymers to create complex patterns with long-range order. [source] Multiple Functionalization of Mesoporous Silica in One-Pot: Direct Synthesis of Aluminum-Containing Plugged SBA-15 from Aqueous Nitrate Solutions,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2008Y. Wu Abstract Aluminum-containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X-ray diffraction, transmission electron microscopy, and N2 sorption measurements show that the Al-containing plugged silicas possess well-ordered hexagonal mesostructures with high surface areas (700,860 m2,g,1), large pore volume (0.77,1.05 cm3,g,1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma,atomic emission spectrometry results show that 0.7,3.0 wt,% aluminum can be introduced into the final samples. 27Al MAS NMR results display that about 43,60% aluminum species are incorporated into the skeleton of the Al-containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al-containing plugged silica has a similar morphology to that of traditional SBA-15. Furthermore, the Al-containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities. [source] Low Molecular Weight Gelators with Hexagonal Order in Their Liquid-Crystal Phases and Gel States: 5-Cyano-2-(3,4,5-trialkoxybenzoylamino)tropones,ADVANCED MATERIALS, Issue 10 2003M. Hashimoto 5-Cyano-2-(3,4,5-trialkoxybenzoylamino)tropones form hexagonal structures in both liquid-crystalline and gel states. The Figure shows an environmental scanning electron microscopy image of octanol gels. Hydrogen bonding between the tropone carbonyl group and the NH group of troponoid amides plays an important role in flattening the molecules, allowing tighter packing structures and more stable columnar mesophases and gel states. [source] Supramolecular control of spin-crossover phenomena in lipophilic Fe(II)-1,2,4-triazole complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Keita Kuroiwa Abstract The spin-crossover properties of lipophilic, supramolecular Fe(II) complexes bridged by 4-(3-dodecyloxy)propyl-1,2,4-triazole [Fe(II)(1)3Cl2] were investigated in chloroform and cast films. A purple low-spin (LS) complex in a powdery form was transformed into pale yellow high-spin (HS) polymers by dissolution in chloroform. The formation of lipophilic molecular wires in chloroform was observed with transmission electron microscopy. The casting of chloroform solutions onto solid supports produced purple, transparent films (LS state). The cast films exhibited sluggish spin-crossover (LS , HS) behavior without thermal hysteresis. On the other hand, the cocasting of equimolar dodecanol or tetradecanol with Fe(II)(1)3Cl2 produced composite films in which alcohol molecules were bound to the complex by ionic hydrogen bonding (ROH···Cl,) and van der Waals interactions. At room temperature, the cast films exhibited regular lamellar structures before and after alcohol doping; this was confirmed by wide-angle X-ray diffraction measurements. Interestingly, the Fe(II)(1)3Cl2/CnOH (n = 12 or 14) ternary films showed a reversible abrupt spin crossover accompanied by thermal hysteresis. The observed bistability was related to dynamic structural transformations between lamellar and hexagonal structures. This study provides a novel supramolecular approach to designing spin-crossover polymer films with controlled thermal bistability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5192,5202, 2006 [source] Influence of P,T pre-treatment on thermopower of Czochralski-grown silicon at high pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2004Vladimir V. Shchennikov Abstract For the first time the thermoelectric power of high-pressure phases of Czochralski-grown silicon (Cz-Si) single crystals has been investigated. From the dependence on pressure of the thermopower the phase transitions in Si have been established. The influence of gas pressure (up to 1.5 GPa) and temperature (450,650 °C) pre-treatment on thermoelectric properties of high-pressure phases of Si with tetragonal, orthorhombic and simple hexagonal structures is discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||