Transmission Electron Microscopy Images (transmission + electron_microscopy_image)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science


Selected Abstracts


Fine-microstructure Mediated Efficient Hydrogen Oxidation in Ni/YSZ Anode Fabricated from Novel Co-precipitation Derived Nanocomposites

FUEL CELLS, Issue 2 2010
K. Sato
Abstract Fine-microstructure mediated efficient hydrogen oxidation was demonstrated on nickel/yttria-stabilised zirconia (Ni/YSZ) anode fabricated from NiO/YSZ nanocomposite particles, synthesised via a novel co-precipitation method using YSZ nanoparticles with the average size of 3,nm. Transmission electron microscopy image revealed that nanocomposite particles calcined at 600,°C consisted of homogeneously distributed NiO and YSZ nanocrystals, approximately 5,nm large. The Ni/YSZ anode was fabricated by sintering the screen-printed nanocomposites at 1,300,°C and their subsequent reduction. The anode had a uniform porous microstructure consisting of fine grains in the range of 200,300,nm, and exhibited quite low area-specific resistance (ASR) of 2.29, 0.43 and 0.15,,,cm2 at 600, 700 and 800,°C, respectively. [source]


Biosensor Based on Self-Assembling Glucose Oxidase and Dendrimer-Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

ELECTROANALYSIS, Issue 6 2007
Lihuan Xu
Abstract A novel amperometric glucose biosensor based on layer-by-layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt-DENs layer and an anionic GOx layer. Transmission electron microscopy images and ,-potentials proved the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt-DENs toward H2O2 and special three-dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5,,M, a wide linear range of 5,,M,0.65,mM, a short response time (within 5,s), and high sensitivity (30.64,,A mM,1,cm,2) and stability (80% remains after 30 days). [source]


Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum Oxidxe

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Sang-Wan Ryu
Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source]


Local dynamics in epoxy coatings containing iron oxide nanoparticles by dielectric relaxation spectroscopy

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
G. Kortaberria
Abstract Nanocomposites of photocurable epoxy resin and epoxy-modified iron oxide magnetic nanoparticles were analyzed by dielectric relaxation spectroscopy to study the local dynamics at temperatures well below the glass-transition temperature. Two secondary processes were detected, , and , processes, but the second one was just detected at lower temperatures in the high-frequency part of the spectra and moved out of the frequency range at higher temperatures. Data were fitted to the Havriliak,Negami and Arrhenius models, and the obtained parameters were analyzed. Relaxation times of the , secondary relaxation did not change with the nanoparticle content, but the relaxation strength increased. The increase could not be explained when we took into account the molecular origin of the relaxation. The presence of ferromagnetic nanoparticles enhanced the internal field and increased the relaxation strengths. Transmission electron microscopy images showed that the nanoparticles were well dispersed in the matrix, without magnetic agglomerates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]


Characterization of end-functionalized styrene,butadiene,styrene copolymers and their application in modified asphalt

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
Qiang Wang
Abstract End amino, carboxylic acid, and hydroxyl functionalized styrene,butadiene,styrene (SBS) triblock copolymers were prepared with 1,5-diazabicyclo[3.1.0]hexane, carbon dioxide, and epoxy ethane as capping agents, respectively. The effects of the end polar groups on the morphology and dynamic mechanical properties were investigated. Transmission electron microscopy images suggested that the group at the end of the polystyrene (PS) segment made the morphology of the PS domains disordered and incompact. Dynamic mechanical results showed that the storage and loss modulus increased after SBS was end-functionalized. End amino and carboxylic acid groups improved the compatibility and storage stability of SBS-modified asphalt. However, the effect of the end-hydroxyl group on the improvement of the storage stability of SBS-modified asphalt was not obvious. The differential scanning calorimetry analysis of SBS-modified asphalt further showed that the compatibility and storage stability of SBS-modified asphalt were improved by the attachment of amino or carboxylic acid groups through the anionic polymerization method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 8,16, 2007 [source]


Electrical Conductivity of Submicrometer Gadolinia-Doped Ceria Sintered at 1000°C Using Precipitation-Synthesized Nanocrystalline Powders

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008
Pandurangan Muralidharan
A simple synthetic strategy has been implemented to obtain low-temperature sintered fine grain size gadolinia-doped ceria, Ce0.9Gd0.1O1.95, (CGO) electrolyte pellets with a high density using weakly agglomerated particles of calcined nanopowders synthesized by a homogeneous precipitation process. The precipitants used were diethylamine (DEA process) and ammonium hydroxide in neutral precipitation (NP process). X-ray diffraction patterns revealed the single-phase crystalline CGO of a fluorite-type structure. The crystalline powder was directly synthesized from solution by the DEA process at room temperature, whereas the NP process powder was crystallized upon hydrothermal treatment at an elevated temperature. Transmission electron microscopy images showed homogeneously dispersed spherical-shaped particles of ,5 nm size for nanopowders calcined at 300°C for 4 h. A high densification range from ,96% to 99% of the theoretical was achieved for the nonconventionally low-temperature sintered pellets at 1000°C from weakly bonded particles of CGO nanopowders calcined at 300°C for 4 h without any sintering aid. The dense CGO pellets sintered at 1000°C for 4 h with an average grain size of ,150,300 nm exhibited a promising high electrical conductivity of 2.03 × 10,2 S/cm (DEA process) and 2.17 × 10,2 S/cm (NP process), measured at 650°C, and low activation energy Ea. The electrical conductivities of fine grain size low-temperature sintered CGO pellets are comparable with the literature reports of sintered pellets using sintering aids, and high-temperature sintered CGO pellets above 1300°C with a larger grain size. [source]


A Scalable Route to Highly Functionalized Multi-Walled Carbon Nanotubes on a Large Scale

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2008
Xianhong Chen
Abstract A scalable and solvent-free chemical process to obtain highly functionalized and dispersible multi-walled carbon nanotubes is reported. Highly functionalized multi-walled carbon nanotubes have been prepared using in situ generated aryl diazonium salts in the presence of ammonium persulfate and 2,2,-azoisobutyronitrile by solvent-free techniques. In the Raman spectra of the resulting materials, characteristic peaks, the D- and G-bands, are shifted by about 10 cm,1 to lower frequencies. At the same time, the relative intensity ratios between the D- and G-bands increase in comparison to that in the spectrum of the purified product. Fourier-transform infrared spectroscopy reveals the presence of the functional groups on the surface. Transmission electron microscopy images directly confirm the significant build-up of sidewall organic moieties on the treated materials. The weight loss of various functional moieties determined by thermogravimetry,differential scanning calorimetry analysis is about 18,33%. The dispersibility of the functionalized materials in solvents, such as chloroform, tetrahydrofuran, and water, is obviously improved. [source]


Thermo-Responsive Hydrogels with Nanodomains: Rapid Shrinking of a Nanogel-Crosslinking Hydrogel of Poly(N -isopropyl acrylamide)

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2008
Nobuyuki Morimoto
Abstract Rapidly shrinking poly(N -isopropyl acrylamide) (PNIPAM) hydrogels are prepared by crosslinking with self-assembled nanogels that consist of cholesteryl- and methacryloyl-substituted pullulan (CHPMA). The CHPMA nanogel (Rh,=,26.4 nm) was used as a crosslinker for a hydrophilic nanodomain. Transmission electron microscopy images of the nanogel-crosslinked PNIPAM hydrogel reveal a well-defined nanoporous structure. The nanogel-crosslinked PNIPAM hydrogel shows rapid shrinking based on its structure. The shrinking half-time was ,2 min, which is about 3,400 times faster than that of a PNIPAM hydrogel crosslinked by methylene(bisacrylamide). [source]


Self-Aligned Nanolenses with Multilayered Ge/SiO2 Core/Shell Structures on Si,(001),

ADVANCED MATERIALS, Issue 2 2007
H.-C. Chen
Selective etching of multilayered Ge-quantum-dot/Si-spacer has been used to fabricate stacked Ge@SiO2 nanolenses with the ability to filter and focus 1.5,,m light. These lenses have potential for use as Si-compatible photodetector materials for telecommunications. The left figure is a schematic sketch of the nanolenses and the right figure is a transmission electron microscopy image of the lenses. [source]


Nanofiber organic semiconductors: The effects of nanosize on the electrical charge transport and optical properties of bulk polyanilines

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009
F. Yakuphanoglu
Abstract The electrical transport, optical, and microstructural properties of bulk polyaniline (PANI) and nano-PANIs were investigated. A field emission scanning electron microscopy (SEM) image of bulk PANI showed macroscopic and aggregated granular particles. A SEM image of the nanostructured PANI showed the formation of one-dimensional nano/microstructures. The formation of nanofibers was observed from the transmission electron microscopy image. The electrical conductivities of the bulk and nanostructured PANIs increased with increasing temperature, which indicated semiconductor behavior. The electrical conductivities of the bulk and nanostructured PANIs at room temperature were found to be 2.12 × 10,5 and 1.80 × 10,2 S/cm, respectively. The electrical conductivity of the nanostructured PANI was about 850 times higher than that of the bulk PANI. The obtained band gaps of the bulk and nanostructured PANIs were determined from diffuse reflectance measurements and were found to be 3.27 and 2.41 eV, respectively. The refractive index of the PANI samples changed from 1.3 to 1.61. The obtained results indicate that the electrical and optical properties of the PANI were inherently dependent on the nanostructure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]


Piezoelectric field around threading dislocation in GaN determined on the basis of high-resolution transmission electron microscopy image

JOURNAL OF MICROSCOPY, Issue 3 2006
G. MACIEJEWSKI
Summary A new method of determining the piezoelectric field around dislocations from high-resolution transmission electron microscopy images is presented. In order to determine the electrical potential distribution near a dislocation core, we used the distortion field, obtained using the geometrical phase method and the non-linear finite element method. The electrical field distribution was determined taking into account the inhomogeneous strain distribution, finite geometry of the sample and the full couplings between elastic and electrical fields. The results of the calculation for a transmission electron microscopy thin sample are presented. [source]


A Chemical Co-Reduction Route to Synthesize Nanocrystalline Vanadium Carbide

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006
Cun Li
Nanocrystalline vanadium carbide (VC) was synthesized via a chemical co-reduction process, in which VCl4 and CCl4 were used as the vanadium source and the carbon source, respectively, and metallic Na as a reductant in an autoclave at 500°C for 12 h. X-ray powder diffraction indicated that the product was an NaCl type of VC with a cell constant a=4.171 Å. A transmission electron microscopy image showed the VC particles were 10,40 nm in size. X-ray photoelectron spectrum and Raman spectrum showed the surface covered with oxide and graphite. The formation of nanocrystalline VC was discussed based on thermodynamics. [source]


Sonochemical synthesis and characterization of ZnO nanorod/Ag nanoparticle composites

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2009
Fei Li
Abstract A simple sonochemical route for the synthesis of Ag nanoparticles on ZnO nanorods is reported. Ultrasonic irradiation of a mixture of ZnO nanorods, Ag(NH3)2+, and formaldehyde in an aqueous medium yields ZnO nanorod/Ag nanoparticle composites. The powder X-ray diffraction of the ZnO/Ag composites shows additional diffraction peaks corresponding to the face-center-cubic structured Ag crystalline, apart from the signals from the ZnO nanorods. Scanning electron microscopy and transmission electron microscopy images of the ZnO/Ag composites reveal that the ZnO nanorods are coated with Ag nanoparticles with a mean size of several tens nanometer. The absorption band of ZnO/Ag composites is distinctly broadened and red-shifted, indicating the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. This sonochemical method is simple, mild and readily scaled up, affording a simple way for synthesis of other composites. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Synthesis and Structure,Property Correlation in Shape-Controlled ZnO Nanoparticles Prepared by Chemical Vapor Synthesis and their Application in Dye-Sensitized Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2009
Revathi R. Bacsa
Abstract Here, the large scale synthesis of nanocrystalline ZnO spheres and tetrapods in the size range of 8,40,nm by chemical vapor synthesis using zinc metal as precursor is described. A detailed study of the effect of experimental parameters on the morphology and yield is presented. High-resolution transmission electron microscopy images of the tetrapods show that they are formed by the self assembly of four nanorods in the vapor phase. The tetrapods have optical absorption coefficients that are one order of magnitude greater than the spheres and show intense UV luminescence whereas the spheres show only the green emission. The observed differences in the optical properties are related to the presence of surface defects present in the nanospheres. The tetrapods have increased efficiencies for application in dye sensitized solar cells when compared to spheres. [source]


Synthesis of Hexagonal-Phase NaYF4:Yb,Er and NaYF4:Yb,Tm Nanocrystals with Efficient Up-Conversion Fluorescence,

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2006
S. Yi
Abstract IR-to-visible up-conversion fluorescent nanocrystals of hexagonal-phase NaYF4:20,%Yb,2,%Er and NaYF4:20,%Yb,2,%Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF3COO)3Y, (CF3COO)3Yb, and (CF3COO)3Er/(CF3COO)3Tm in oleylamine at 330,°C. The average particle size is 10.5,±,0.7,nm (from random measurements of 200,particles from five transmission electron microscopy images) and 11.1,±,1.3,nm (from dynamic-light-scattering measurements). The up-conversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic-phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal-phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes. [source]


Cover Picture: Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006
Mater.
Abstract Hollow nanocrystals have been synthesized through a mechanism analogous to the Kirkendall Effect. When a cobalt nanocrystal reacts with sulfur in solution, the outward diffusion of cobalt atoms is faster than the inward diffusion of sulfur atoms through the sulfide shell. The dominating outward diffusion of cobalt cations produces vacancies that can condense into a single void in the center of the nanocrystal at high temperatures. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds and is described in the Full Paper by A.,P. Alivisatos and co-workers on p.,1389. Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at >,120,°C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature-dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell-size statistics and transmission electron microscopy images of as-grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system. [source]


Kinetics of Formation and Physicochemical Characterization of Thermally-Induced ,-Lactoglobulin Aggregates

JOURNAL OF FOOD SCIENCE, Issue 5 2010
R.N. Zúñiga
Abstract:, The kinetics of heat denaturation and aggregation for ,-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 °C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native ,-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for ,-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant,k,= 7.5, 6.3 and 5.6 × 10,3 s,1 were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for ,-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. ,-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for ,-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods. [source]


Piezoelectric field around threading dislocation in GaN determined on the basis of high-resolution transmission electron microscopy image

JOURNAL OF MICROSCOPY, Issue 3 2006
G. MACIEJEWSKI
Summary A new method of determining the piezoelectric field around dislocations from high-resolution transmission electron microscopy images is presented. In order to determine the electrical potential distribution near a dislocation core, we used the distortion field, obtained using the geometrical phase method and the non-linear finite element method. The electrical field distribution was determined taking into account the inhomogeneous strain distribution, finite geometry of the sample and the full couplings between elastic and electrical fields. The results of the calculation for a transmission electron microscopy thin sample are presented. [source]


The Role of Functional Group on the Exfoliation of Clay in Poly(L -lactide)

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 3 2005
Guang-Xin Chen
Abstract Summary: A new method was attempted to improve the interaction between poly(L -lactide) (PLLA) with a commercially available organoclay, Cloisite 25A (C25A), which was functionalized with (glycidoxypropyl)trimethoxysilane to introduce epoxy groups, and is referred to as twice-functionalized organoclay (TFC). Tethering PLLA molecules to the epoxy groups on the surface of the TFC was attempted by melt compounding. X-Ray diffraction and transmission electron microscopy images showed that fully exfoliated PLLA/TFC nanocomposites were prepared successfully. Transmission electron micrographs of the PLLA composites of the three clays used here. [source]


Structural analysis of pyramidal defects in Mg-doped GaN

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
A. Pretorius
Abstract Pyramidal defects in GaN:Mg grown by metalorganic vapour phase epitaxy are studied by high resolution transmission electron microscopy, energy dispersive X-ray analysis and scanning transmission electron microscopy. High resolution transmission electron microscopy images were simulated using the multislice approach in order to analyse the basal plane of the pyramidal defects. The simulated images were compared quantitatively with the experimental images. Two structural models for the basal plane inversion domain boundary containing antibixbyite-type layers are presented which show the best observed agreement with the experimentally found inversion domain boundary. Nevertheless, both models still do not match the experimental images satisfactorily, indicating that some other structure than antibixbyite is present at the boundary. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]