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Field-emission Scanning Electron Microscopy (field-emission + scanning_electron_microscopy)
Selected AbstractsLow-Temperature Synthesis of Phase-Pure 0D,1D BaTiO3 Nanostructures Using H2Ti3O7 TemplatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2010Duk Kyu Lee Abstract One-dimensional (1D) barium titanate (BaTiO3) nanowires, which were uniformly covered with 0D BaTiO3 nanocrystals, were synthesized by using a simple solvothermal reaction of protonated trititanate (H2Ti3O7) nanowires with barium hydroxide octahydrate [Ba(OH)2·8H2O] at 80 °C in ethanol/water mixed solvent systems. The compositions of the mixed solvents , the volume ratio of ethanol to deionized water , was a key controlling parameter in order to determine the phase formation and primary particle size of the 0D BaTiO3 nanocrystals. Single-phase cubic perovskite BaTiO3 started to form at 80 °C in a mixed solvent containing more than approximately 60,% by volume of ethanol. Field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) analysis revealed that the as-prepared BaTiO3 retained its wire-shaped morphology with nanocrystals on the surface. Furthermore, the synthetic mechanism of the 0D-1D BaTiO3 nanostructures was demonstrated in view of the dielectric tuning of the mixed solvent and the similarities between the crystal structures of BaTiO3 and H2Ti3O7. [source] Hydrothermal Synthesis of Structure- and Shape-Controlled Manganese Oxide Octahedral Molecular Sieve NanomaterialsADVANCED FUNCTIONAL MATERIALS, Issue 9 2006W.-N. Li Abstract Highly uniform single-crystal Na-OMS-2 (OMS: octahedral molecular sieve), pyrolusite, and ,-MnO2 nanostructures with an interesting 3D urchinlike morphology have been successfully prepared using a hydrothermal method based on a mild and direct reaction between sodium dichromate and manganese sulfate. The crystal phases, shapes, and tunnel sizes of the manganese dioxide nanostructures can be tailored. Reaction temperature, concentrations of the reactants, and acidity of the solution play important roles in controlling the synthesis of these manganese dioxides. Field-emission scanning electron microscopy and transmission electron microscopy (TEM) studies show that the nanomaterials obtained are constructed of self-assembled nanorods. X-ray diffraction and TEM results indicate that the constituent manganese dioxide particles are single-crystalline materials. Energy dispersive X-ray analysis and magnetic studies imply that chromium cations may be incorporated into the framework and/or tunnels of the manganese dioxides. A mechanism for the growth of manganese dioxides with urchinlike architectures is proposed. [source] Preparation of ReFeO3 nanocrystalline powders by auto-combustion of citric acid gelASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Anhua Wu Abstract Autocombustion of citric acid gel was employed to prepare ReFeO3 (Re = Gd, Nd) nanocrystalline powders. The phase identification and lattice parameters were investigated by the X-ray diffraction (XRD). Field-emission scanning electron microscopy (FESEM) investigations were carried out to examine the morphology and average size of these powders. Several one phonon lines, two-magnon excitation, and two-phonon scattering have been assigned in their Raman spectra. Both NdFeO3 and GdFeO3 nanocrystalline powders were single ReFeO3 phase, which are agglomerated with average crystallite size of 70,90 nm. The investigations indicated that the autocombustion of citric acid gel method is an effective technology to prepare ReFeO3 nanocrystalline powders. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Synthesis of highly-ordered hierarchical ZnO nanostructures and their application in dye-sensitized solar cellsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010Y. F. Zhu Abstract In order to improve the performance of ZnO-based solar cells, highly-ordered hierarchical ZnO nanostructures were design and fabricated. The hierarchical nanostructures were grown on FTO (fluorine doped tin oxide, SnO2:F) glass substrates via a facile, low-temperature, and low-cost chemical route. The morphology and structure of the obtained products has been confirmed by field-emission scanning electron microscopy and X-ray diffraction measurements. The performance investigation of the prepared dye-sensitized solar cells (DSSCs) demonstrates that the hierarchical ZnO nanostructure-based solar cell shows a higher short-circuit current density compared with the ZnO nanowire counterpart. The enhanced current density may be due to the fact that the surface area of the hierarchical nanostructures is increased. These results indicate that hierarchical ZnO nanostructures are more suitable for the application as photoelectrode of DSSCs. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solvothermal growth of single-crystal hexagonal prismatic SrCO3 microrodsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007Fanglin Du Abstract Single-crystal hexagonal prism SrCO3 microrods have been prepared by a simple solvothermal route. The effects of the reaction time, the content of 1,2-propanediol and the reactants mass on the products have been investigated, respectively. The as-synthesized microrods were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results reveal that the products have uniform shape and excellent monodispersity. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tartatric Acid and L -Cysteine Synergistic-Assisted Synthesis of Antimony Trisulfide Hierarchical Structures in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Jun Pan Abstract Alveolate amorphous Sb2S3 microspheres about 2 ,m in diameter were hydrothermally synthesized in aqueous solution without the use of a surfactant at 180 °C by using SbCl3, L -cysteine, and tartaric acid as starting materials. After annealing at 250 °C for 3 h under a nitrogen atmosphere, polycrystalline Sb2S3 hollow spheres were obtained. The morphology, structure, and phase composition of alveolate Sb2S3 microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. It was demonstrated that tartaric acid and L -cysteine play a key role in the formation of such hierarchical structures. In addition, the possible aggregation mechanism was proposed to illustrate the formation of Sb2S3 microspheres on the basis of the experimental results and analyses.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Specific Functionalization of Carbon Nanotubes for Advanced Polymer NanocompositesADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Nanda Gopal Sahoo Abstract A novel approach to chemically functionalize multiwalled carbon nanotubes (MWCNTs) for making advanced polymeric nanocomposites with liquid crystalline polymers (LCPs) is presented. In this approach, two types of chemical moieties (i.e., carboxylic and hydroxyl benzoic acid groups) are selectively introduced onto the sidewalls of the MWCNTs. Fourier transform IR and Raman spectroscopy are used to examine the interaction between the functionalized MWCNTs and the LCP. The strong interaction between the functionalized MWCNTs and the LCP greatly improved the dispersion of MWCNTs in the polymer matrix as well as the interfacial adhesion. The dispersion of the MWCNTs in the LCP matrix is observed by optical microscopy and field-emission scanning electron microscopy. As a result, the addition of 1,wt% MWCNTs in the LCP resulted in the significant improvement (41 and 55%) in the tensile strength and modulus of the LCP. [source] Organic Photovoltaic Cells Based On Solvent-Annealed, Textured Titanyl Phthalocyanine/C60 HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Diogenes Placencia Abstract Organic photovoltaic cells (OPV) with good near-IR photoactivity are created from highly textured titanyl phthalocyanine (TiOPc)/C60 heterojunctions. Vacuum deposited TiOPc thin films are converted to the near-IR absorbing "Phase II" polymorph using post-deposition solvent annealing. The Phase I,,,Phase II transition broadens the absorbance spectrum of the Pc film producing absorptivities (,,,,105,cm,1) from 600,900,nm, along with substantial texturing of the Pc layer. Atomic force microscopy and field-emission scanning electron microscopy of the solvent annealed films show that the surface roughness of the Pc layers is increased by a factor of greater than 2× as a result of the phase transformation. Current,voltage (J,V) responses for white light illumination of ITO (100,nm)/TiOPc (20,nm)/C60 (40,nm)/BCP (10,nm)/Al (100,nm) OPVs show a near doubling of the short-circuit photocurrent (JSC), with only a small decrease in open-circuit photopotential (VOC), and a concomitant increase in power conversion efficiency. Incident photon current efficiency (IPCE) plots confirmed the enhanced near-IR OPV activity, with maximum IPCE values of ca. 30% for devices using Phase II-only TiOPc films. UV-photoelectron spectroscopy (UPS) of TiOPc/C60 heterojunctions, for both Phase I and Phase II TiOPc films, suggest that the Phase II polymorph has nearly the same HOMO energy as seen in the Phase I polymorph, and similar frontier orbital energy offsets, EHOMOPc,ELUMOC60, leading to comparable open-circuit photovoltages. These studies suggest new strategies for the formation of higher efficiency OPVs using processing conditions which lead to enhance near-IR absorptivities, and extensive texturing of crystalline donor or acceptor films. [source] Stabilization of PbS Nanocrystals by Bovine Serum Albumin in its Native and Denatured StatesADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Mandeep Singh Bakshi Abstract PbS nanocrystals (NCs) are synthesized in aqueous phase within a temperature range of 40,80,°C in the presence of native and denatured states of bovine serum albumen (BSA) as the capping/stabilizing agent. The NCs are characterized with the help of field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray analysis. At 40,°C, large ball-shaped NCs (145,±,37,nm) with small surface protrusions are formed when 1,×,10,4,g mL,1 BSA is used. As the reaction temperature is increased towards 80,°C, the size of NCs decreases and they acquire somewhat cubic geometries (49.1,±,7.0,nm) due to a change in the capping behavior of BSA between its native and denatured states. The native and denatured states of BSA are simultaneously studied by fluorescence spectroscopy using tryptophan emission, and pH measurements with respect to time and temperature. Gel electrophoresis is used to determine the polarity of the BSA capped NCs. Only the small sized NCs conjugated with relatively larger amounts of BSA show a displacement towards the positively charged electrode in comparison to larger NCs with lower amounts of BSA capping. It was concluded that the denatured state of BSA is more effective in controlling the crystal growth of PbS than its native state especially in the low concentration range. [source] Electrically Conductive Thin Films Prepared from Layer-by-Layer Assembly of Graphite PlateletsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Mubarak Alazemi Abstract Layer-by-layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/,, -methacryl-oxyethyl-trimethyl-ammonium copolymer as the cationic binder. Nanoparticle zeta (,,) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field-emission scanning electron microscopy and atomic-force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self-assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21,nm. Thin-film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6,m,,cm,2 at 173,nm to 3.5,m,,cm,2 at 276,nm. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly. [source] Template Synthesis of Aligned Carbon Nanotube Arrays using Glucose as a Carbon Source: Pt Decoration of Inner and Outer Nanotube Surfaces for Fuel-Cell Catalysts,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2008Zhenhai Wen A facile method is developed to synthesize aligned arrays of open-ended carbon nanotubes (CNTs) via in situ glucose polymerization in the inner pores of anodic aluminum oxide templates under hydrothermal conditions, followed by carbonization at high temperature. Pt nanoparticles are decorated on the surfaces of the as-prepared CNTs using the incipient wet method based on the use of NaBH4 as a reductant. Characterization of the resulting structures by transmission electron microscopy and field-emission scanning electron microscopy demonstrates that the Pt nanoparticles are anchored on both the inner and outer walls of CNTs, thus giving rise to a shell,core,shell-like nanotube composite. The electrocatalytic properties of the Pt,CNT,Pt electrodes are investigated for methanol oxidation by cyclic voltammetry and chronoamperometric measurements. It is found that the hybrid electrodes show superior catalytic performance compared to commercial carbon-black-supported Pt. The increased catalytic efficiency of Pt might be a result of the unique morphology of these structures. [source] Single-Crystalline Gallium Nitride Microspindles: Synthesis, Characterization, and Thermal Stability ,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2004F. Xu Abstract This paper describes a facile procedure for synthesizing high-quality gallium nitride microspindles on a large scale using a solid-state reaction of GaI3, NaNH2, and NH4Cl in a sealed system at 500,°C for 6,h. The structures, compositions, and morphologies of the as-synthesized products are derived from X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images show that the as-synthesized GaN spindles are composed of many single-crystalline platelets. The GaN microspindles show different optical properties depending on their shape (e.g., nanowires or nanoparticles) in photoluminescence (PL) emission spectroscopy and Raman spectroscopy. The possible growth mechanism of GaN microspindles is controlled by linear kinetics with a driving force proportional to the difference between a local supersaturation and an equilibrium chemical potential. Furthermore, the thermal stability of the GaN microspindles is investigated under various annealing conditions and discussed on the basis of additional TEM and XRD analyses. [source] Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2003Y.-P. Fang Abstract In this paper, Tb(OH)3 and Y(OH)3 single-crystalline nanotubes with outer diameters of 30,260,nm, inner diameters of 15,120,nm, and lengths of up to several micrometers were synthesized on a large scale by hydrothermal treatment of the corresponding oxides in the presence of alkali. In addition, Tb4O7 and Y2O3 nanotubes can be obtained by calcination of Tb(OH)3 and Y(OH)3 nanotubes at 450,°C. X-ray diffraction (XRD), field-emission scanning electron microscopy, transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry, and differential scanning calorimetry (DSC) have been employed to characterize these nanotube materials. The growth mechanism of rare earth hydroxide nanotubes can be explained well by the highly anisotropic crystal structure of rare earth hydroxides. These new types of rare earth compound nanotubes with open ends have uses in a variety of promising applications such as luminescent devices, magnets, catalysts, and other functional materials. Advantages of this method for easily realizing large-scale production include that it is a simple and unique one-pot synthetic process without the need for a catalysts or template, is low cost, has high yield, and the raw materials are readily available. The present study has enlarged the family of nanotubes available, and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials. [source] Enhanced Sensitivity of a Gas Sensor Incorporating Single-Walled Carbon Nanotube,Polypyrrole Nanocomposites,ADVANCED MATERIALS, Issue 12 2004H. An A nanocomposite of polypyrrole/carbon nanotubes prepared by in situ chemical polymerization shows improved conductivity of the polypyrrole as compared with its pure form. Its application as a chemical sensor, made using a simple spin-casting technique, shows a drastically increased sensitivity. The Figure shows a field-emission scanning electron microscopy (FE-SEM) image of the SWNT/Ppy nanocomposite. [source] Sperm head morphology in 36 species of artiodactylans, perissodactylans, and cetaceans (Mammalia)JOURNAL OF MORPHOLOGY, Issue 2 2005Amy Downing Meisner Abstract Detailed descriptions of mammalian sperm morphology across a range of closely related taxa are rare. Most contributions have been generalized descriptions of a few distantly related mammalian species. These studies have emphasized a generalized ungulate sperm morphology, but have not underscored several important morphological differences in ungulate sperm, such as head shape. The present study is the first to document descriptions of sperm head morphology using cold field-emission scanning electron microscopy (FE-SEM) for a large number of closely related mammalian species. In total, the sperm of 36 species in three orders: Artiodactyla (even-toed ungulates), Cetacea (whales, porpoises, and dolphins), and Perissodactyla (odd-toed ungulates) were examined to gather new information relevant to the debate about the phylogenetic placement of cetaceans relative to terrestrial ungulates. In all species examined, the sperm heads were generally flattened and ovate in shape with a distinct apical ridge, although considerable variation in sperm head shape was detected, both within and between orders. In artiodactylans, the sperm head was uniformly flat in lateral view, whereas perissodactylan and cetacean sperm heads showed a distinct posterior thickening. In both artiodactylans and perissodactylans, the mitochondria were elongate and wound in a tight helix around the midpiece, whereas in cetaceans the mitochondria were rounded and appeared to be randomly arranged around the midpiece. Additionally, prominent ridges running along the anterior,posterior axis were observed in the postacrosomal region of the sperm head in four species of cetaceans. These ridges were not observed in any of the terrestrial ungulates examined. Pits or fenestrations were detected in the postacrosomal region in most artiodactylan species examined; these structures were not detected in perissodactylans or cetaceans. The equatorial segment of the acrosome was detected in the artiodactylan species examined, tentatively identified in perissodactylans, but not found in cetaceans. Its shape and location are described for relevant taxa. The presence of a recently reported substructure within the equatorial segment (the equatorial subsegment; Ellis et al. [2002] J Struct Biol 138:187,198) was detected in artiodactylans, and its shape is described for the species examined. © 2004 Wiley-Liss, Inc. [source] Synthesis and hierarchical superstructures of side-chain liquid crystal polyacetylenes containing galactopyranoside end-groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2009Ming-Shou Ho Abstract Three kinds of chiral saccharide-containing liquid crystalline (LC) acetylenic monomers were prepared by click reaction between 2-azidoethyl-2,3,4,6-tetraacetyl-,- D -galactopyranoside and 1-biphenylacetylene 4-alkynyloxybenzoate. The obtained monomers were polymerized by WCl6 -Ph4Sn to form three side-chain LC polyacetylenes containing 1-[2-(2,3,4,6-tetraacetyl-,- D -galactopyranos-1-yl)-ethyl]-1H -[1,2,3]-triazol-4,-biphenyl 4-alkynyloxybenzoate side groups. All monomers and polymers show a chiral smectic A phase. Self-assembled hiearchical superstructures of the chiral saccharide-containing LCs and LCPs in solution state were studied by field-emission scanning electron microscopy. Because of the LC behavior, the LC molecules exhibit a high segregation strength for phase separation in dilute solution (THF/H2O = 1:9 v/v). The self-assembled morphology of LC monomers was dependent upon the alkynyloxy chain length. Increasing the alkynyloxy chain length caused the self-assembled morphology to change from a platelet-like texture (LC-6) to helical twists morphology (LC-11 and LC-12). Furthermore, the helical twist morphological structure can be aligned on the polyimide rubbed glass substrate to form two-dimensional ordered helical patterns. In contrast to LC monomers, the LCP-11 self-assembled into much more complicate morphologies, including nanospheres and helical nanofibers. These nanofibers are evolved from the helical cables ornamented with entwining nanofibers upon natural evaporation of the solution in a mixture with a THF/methanol ratio of 3:7. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6596,6611, 2009 [source] Raman spectroscopic evaluation of polyacrylonitrile-based carbon nanofibers prepared by electrospinningJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2004Chan Kim Abstract Poly(acrylonitrile) (PAN) solutions in N,N -dimethylformamide were electrospun into webs consisting of 350 nm ultra-fine fibers. The webs were oxidatively stabilized and followed by heat treatment in the range of 700,1000°C. Characterization of the microstructure of PAN-based carbon nanofibers was performed by x-ray diffraction, field-emission scanning electron microscopy, electrical conductivity and Raman spectroscopy. The Lc(002) and La(10) values were calculated to be 1.85,2.15 and 2.23,3.36 nm, respectively. The Lc(002) and La(10) values increased by about 86% and 66%, respectively, when the heat treatment temperature (HTT) was increased from 700 to 1000°C. The electrical conductivity of carbonized PAN nanofiber webs increased with increasing carbonization temperature, being 6.8 × 10,3 and 1.96 S cm,1 at 700 and 1000°C, respectively. The D and G bands from Raman scattering were fitted into a Gaussian,Lorentzian hybridized function, and the crystallite sizes in the nanofibers were evaluated from the R -values determined from the ratios of the intensity of the G band to that of the D band. The domain size of the graphitic layers was in the range 1.6,3.2 nm with higher values at higher HTT. Copyright © 2004 John Wiley & Sons, Ltd. [source] Fast and Almost Complete Nitridation of Mesoporous Silica MCM-41 with Ammonia in a Plug-Flow ReactorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Fumitaka Hayashi The title reaction proceeded well to yield silicon (oxy)nitride at 973,1323 K using a plug-flow reactor. The degree of nitridation was studied as a function of temperature and time of nitridation, the sample weight, and the flow rate of ammonia. It was dependent on the reaction temperature and the amount of ammonia supplied per sample weight. The nitridation at 1273 K for 10,25 h yielded the oxynitride with 36,39 wt% nitrogen, which was very close to 40 wt% of Si3N4. Characterization with X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy measurements, and nitrogen adsorption revealed the conversion of MCM-41 to the corresponding oxynitride without essential loss of the mesoporous structure, the decrements of the lattice constant and the pore diameter by 20,35%, and the increments of the wall thickness by ca. 45%. Solid-state 29Si nuclear magnetic resonance spectra during the nitridation clearly showed fast decrease in SiO4 species and slow in SiO3(OH). Various intermediate species, SiOxNy(NH2 or NH)z, were observed to be formed and finally, ca. 70% SiN4 species, ca. 20% SiN3(NH2 or NH), and ca. 10% SiON2(NH2 or NH) were produced, being consistent with the results of the above mentioned elemental analysis. [source] Silver Nanoparticles Stabilized by Thermoresponsive Microgel Particles: Synthesis and Evidence of an Electron Donor-Acceptor EffectMACROMOLECULAR RAPID COMMUNICATIONS, Issue 24 2007Yang Dong Abstract Well-dispersed silver nanoparticles were successfully fabricated within poly[(N -isopropylacrylamide)- co -(acrylic acid)] [P(NIPAM- co -AA)] microgel particles which were synthesized with different cross-linking densities. Their structures were studied by field-emission scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, X-ray diffraction and FT-IR spectroscopy. The interactions between the microgel particles and the incorporated silver nanoparticles were investigated by X-ray photoelectron spectroscopy. The results revealed that there was charge transfer from the carbonyl groups of the microgel particles to the silver nanoparticles. Moreover, as the diameter of the AgNPs decreases, the charge-transfer efficiency increases accordingly. The P(NIPAM- co -AA)/AgNPs hybrid microgel particles were thermoresponsive and their behavior completely reversible with several heating/cooling cycles. [source] Synthesis of Large-Area Three-Dimensional Polyaniline Nanowire Networks Using a "Soft Template"MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2005Wenbin Zhong Abstract Summary: Three-dimensional polyaniline (PANI) nanowire networks were synthesized in high yield using a "soft template" self-assembled with hexadecyltrimethylammonium bromide and oxalic acid. The PANI nanowire networks had diameters from 35,100 nm depending on synthesis conditions and/or procedures. The networks and the "cross-linking points" were clearly observed by field-emission scanning electron microscopy and transmission electron microscopy. A possible mechanism for the formation of three-dimensional PANI nanowire networks is discussed. FESEM image of PANI with three-dimensional nanowire networks. [source] Unintentionally doped InN grown onto an atomically flat AlN intermediate layer using plasma-assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006K. R. Wang Abstract Unintentionally doped InN has been grown onto an atomically flat AlN intermediate layer on top of the Si(111) substrate using plasma-assisted molecular beam epitaxy (PA-MBE). Though there are lots of micrometer-size indium droplets randomly distributed on the top of the surface, the highest electron mobility of this InN thin film measured at room temperature by van der Pauw method is still higher than 1000 cm2/V s with a carrier concentration of 5,8.9 × 1018 cm,3. A symmetrical X-ray rocking curve is measured and the full-width-at-half-maximum (FWHM) of this sample is 1089 arcsec. In the meantime, the threading dislocation (TD) density of this material is estimated to around 9.8 × 108 cm,2 , 7.5 × 109 cm,2 depending on the probing regions that are studied by the etching technique and field-emission scanning electron microscopy (FE-SEM). (2 × 1) in situ reflection high-energy electron diffraction (RHEED) patterns show that this sample is grown under In-rich environment with possible In-terminated surface. From the FE-SEM pictures which were taken from the samples after 10 minutes etching in hydrochloride, the surface morphology shows In-polarity-like patterns that coincide with those procured in RHEED. To select and grow a high-quality laminated AlN as intermediate layer is believed to be the major step in obtaining this high electron mobility InN thin film on Si substrate. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2004Sang Hyub Han Abstract Preparation of a polyimide nanofoam (PI-F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)-co-(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4,-oxydianiline (ODA). The precursor was then grafted with bromide-terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N -methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X-ray scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The morphology showed nanophase-separated structures with uniformly distributed and non-interconnected pores of 20,40,nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd. [source] Calcification of articular cartilage in human osteoarthritisARTHRITIS & RHEUMATISM, Issue 9 2009M. Fuerst Objective Hypertrophic chondrocyte differentiation is a key step in endochondral ossification that produces basic calcium phosphates (BCPs). Although chondrocyte hypertrophy has been associated with osteoarthritis (OA), chondrocalcinosis has been considered an irregular event and linked mainly to calcium pyrophosphate dihydrate (CPPD) deposition. The aim of this study was to determine the prevalence and composition of calcium crystals in human OA and analyze their relationship to disease severity and markers of chondrocyte hypertrophy. Methods One hundred twenty patients with end-stage OA undergoing total knee replacement were prospectively evaluated. Cartilage calcification was studied by conventional x-ray radiography, digital-contact radiography (DCR), field-emission scanning electron microscopy (FE-SEM), and synovial fluid analysis. Cartilage calcification findings were correlated with scores of knee function as well as histologic changes and chondrocyte hypertrophy as analyzed in vitro. Results DCR revealed mineralization in all cartilage specimens. Its extent correlated significantly with the Hospital for Special Surgery knee score but not with age. FE-SEM analysis showed that BCPs, rather than CPPD, were the prominent minerals. On histologic analysis, it was observed that mineralization correlated with the expression of type X collagen, a marker of chondrocyte hypertrophy. Moreover, there was a strong correlation between the extent of mineralization in vivo and the ability of chondrocytes to produce BCPs in vitro. The induction of hypertrophy in healthy human chondrocytes resulted in a prominent mineralization of the extracellular matrix. Conclusion These results indicate that mineralization of articular cartilage by BCP is an indissociable process of OA and does not characterize a specific subset of the disease, which has important consequences in the development of therapeutic strategies for patients with OA. [source] Structural Characterization of Cobalt Thin Films Grown by Metal-Organic CVD,CHEMICAL VAPOR DEPOSITION, Issue 5 2005F. Chioncel Abstract Cobalt thin films were produced by metal-organic CVD from C5H5Co(CO)2, at various temperatures and for various deposition times. The films have been grown onto glass substrates with no buffer. The crystalline structure, morphology, and composition of the films were analyzed by X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and Auger electron spectroscopy (AES). Routine XRD patterns were collected in symmetric geometry for phase identification and the sin2, diffraction technique was employed to calculate the average in-plane stress. Structural studies indicate that the films tend to grow in island mode, as predicted by theory, and have a structure between that of face-centered cubic (fcc) and hexagonal close-packed (hcp) cobalt. There is significant in-plane tensile stress at the interface with the substrate, which relaxes to a compressive stress an order of magnitude lower at the surface. The films have a relatively low impurity content, as determined by AES, except near the surface. [source] Fabrication of Luminescent CdS Nanoparticles on Short-Peptide-Based Hydrogel Nanofibers: Tuning of Optoelectronic PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009Goutam Palui Abstract The pH-induced self-assembly of three synthetic tripeptides in water medium is used to immobilize luminescent CdS nanoparticles. These peptides form a nanofibrillar network structure upon gelation in aqueous medium at basic pH values (pH,11.0,13.0), and the fabrication of CdS nanoparticles on the gel nanofiber confers the luminescent property to these gels. Atomic force microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy clearly reveal the presence of CdS nanoparticles in a well-defined array on the gel nanofibers. This is a convenient way to make organic nanofiber,inorganic nanoparticle hybrid nanocomposite systems. The size of the CdS nanoparticles remains almost same before and after deposition on the gel nanofiber. Photoluminescence (PL) measurement of the CdS nanoparticles upon deposition on the gel nanofibers shows a significant blue shift in the emission spectrum of the nanoparticles, and there is a considerable change in the PL gap energy of the CdS nanoparticles after immobilization on different gel nanofibrils. This finding suggests that the optoelectronic properties of CdS nanoparticles can be tuned upon deposition on gel nanofibers without changing the size of the nanoparticles. [source] Tetraethylenepentamine-Directed Controllable Synthesis of Wurtzite ZnSe Nanostructures with Tunable MorphologyCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2008Baojuan Xi Dr. Abstract A novel tetraethylenepentamine (TEPA)-directed method has been successfully developed for the controlled synthesis of ZnSe particles with distinctive morphologies, including nanobelts, nanowires, and hierarchically solid/hollow spheres. These structures, self-assembled from nanobelts and nanorods, have been synthesized by adjusting the reaction parameters, such as the solvent composition, reaction temperature, and the aging time. Results reveal that the volume ratio of H2O and TEPA plays a crucial role in the final morphology of ZnSe products. The mechanisms of phase formation and morphology control of ZnSe particles are proposed and discussed in detail. The products have been characterized by means of X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM), selected area electron diffraction, high-resolution TEM, Raman spectra and luminescence spectroscopy. The as-prepared ZnSe nanoparticles display shape- and size-dependent photoluminescent optical properties. This is the first time to report preparation of complex hollow structures of ZnSe crystals with hierarchy through a simple solution-based route. This synthetic route is designed to exploit a new H2O/TEPA/N2H4,H2O system possibly for the preparation of other semiconductor nanomaterials. [source] | |||||||||||||||||||||||||||||||