Simple extraction‐solvothermal synthesis of single‐crystalline silver microplates

Single‐crystalline silver microplates, with average edge length of about 1.5 μm and thickness of 100 nm, have been synthesized by a simple extraction‐solvothermal method. Samples were characterized in detail by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and High‐resolution transmission electron microscopy (HRTEM) technologies. Extractant primary amine N1923 can also act as reducing agent. It has been found that microstructure of the silver can be controlled by the n‐octanol during the solvothermal treatment. Based on a series of experimental analysis, the possible formation mechanism of these microplates was discussed briefly. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile morphology‐controlled hydrothermal synthesis of flower‐like self‐organized ZnO architectures

Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)₂ and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

PMA‐b‐PAA‐controlled synthesis of one‐dimensional CaCO3 superstructures

Crystallization of calcium carbonate (CaCO₃) crystals by a gas‐liquid diffusion method has been carried out in aqueous solution using a double‐hydrophilic block copolymer (DHBC) poly(maleic anhydride)‐b‐poly(acrylic acid) (PMA‐b‐PAA). The as‐prepared products were characterized with X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), high‐resolution transmission electron microscopy (HRTEM) and infrared spectroscopic analysis (FT‐IR). Uniform one‐dimensional calcite micro/nanostructures with different morphologies are fabricated through an assembled process. The influence of PMA‐b‐PAA copolymer concentration on the morphology of calcite nano/microwires is investigated, which plays an important role in the morphological control of building blocks composed of one‐dimensional calcite crystals. The possible formation mechanism of one‐dimensional CaCO₃ crystals was discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of silicon thin films by current‐induced joule heating using a tungsten overcoat

A modified crystallization process using current‐induced joule heating under vacuum is presented. A thin layer of high temperature resistant tungsten was sputtered on the amorphous silicon as the conducting and annealing medium. The thin film thickness was measured by α‐stepper. The high current density provided effective means in crystallizing the amorphous silicon layer. The crystalline morphology was studied by scanning electron microscopy (SEM) after Secco‐etch, transmission electron microscopy (TEM), and x‐ray diffraction (XRD), under different annealing conditions. The grain size was controlled in the range of 0.1‐0.5 μm and could be increased with annealing time. No tungsten silicide was found. Some defects were formed due to electron‐migration effect near the electrodes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wet‐chemical synthesis and characterization of NiBi nano‐ and micro‐particles

Preparation and characterization of NiBi nano‐ and micro‐particles are presented. Firstly, predetermined compositions were obtained by simultaneous precipitation from solutions of Bi(NO₃)₃ and Ni(NO₃)₂. The precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow at 673 K. Correlation between the predetermined and the actual compositions of the products was found. Characterization of the precipitates was carried out employing X‐ray diffraction, scanning and transmission electron microscopy. Nickel‐bismuth intermetallic phase (NiBi) particles with nano‐ and micro‐dimensions were observed in the samples after reduction. The other possible Ni–Bi intermediate phase (NiBi₃) did not form at these conditions although its presence was expected according to the phase diagram. This finding might be useful for the implementation of Bi‐based solders where the growth of the compound NiBi₃ in the solder joints must be prevented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Capsule‐like α‐Fe2O3 nanoparticles: Synthesis,characterization, and growth mechanism

Uniform capsule‐like α‐Fe₂O₃ particles were synthesized via a simple hydrothermal method, employing FeCl₃ and CH₃COONa as the precursors and sodium dodecyl sulfate (SDS) as soft template. X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy were used to characterize the structure of synthesized products. Some factors influencing the formation of capsule‐like α‐Fe₂O₃ particles were systematically investigated, including different kinds of surfactants, the concentration of SDS, and reaction times. The investigation on the evolution formation reveals that SDS was critical to control the morphology of final products, and a possible five‐step growth mechanism was presented by tracking the structures of the products at different reaction stages.     

Preparation of crystalline fibres of codoped BaAl2O4:Eu2+:Cr3+

Phosphor material BaAl₂O₄:Eu²⁺, Cr³⁺ with varying concentrations of Cr co‐doping were prepared by solid‐state synthesis method. Crystalline fibres were obtained by controlled annealing temperature. Synthesized compositions were characterized for their phase and crystallinity by powder x‐ray diffraction. The crystalline morphology was investigated using SEM analysis. High resolution transmission electron microscopy (HRTEM) in image and diffraction modes was used to investigate the microstructure. The effect of Cr doping on quality and morphology of grown crystals was investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.     

Low‐temperature urea‐assisted hydrothermal synthesis of Bi2S3 nanostructures with different morphologies

Different morphologies of single‐crystalline orthorhombic phase bismuth sulfide (Bi₂S₃) nanostructures, including sub‐microtubes, nanoflowers and nanorods were synthesized by a urea‐assisted hydrothermal method at a low temperature below 120 °C for 12 h. The as‐synthesized powders were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and UV‐vis spectrophotometry. The experimental results showed that the sulfur sources had a great effect on the morphology and size of the resulting powders. The formation mechanism of the Bi₂S₃ nanostructures with different morphologies was discussed. All Bi₂S₃ nanostructures showed an appearance of blue shift relative to the bulk orthorhombic Bi₂S₃, which might be ascribed to the quantum size effect of the final products. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Monodisperse CeO2 sub‐micro spherical aggregates with controllable building blocks

Monodisperse CeO₂ spherical aggregates with diameters ranging from 200 to 300 nm have been successfully synthesized through a facile hydrothermal method. The structure and morphology of the samples were characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and field‐emission scanning electron microscopy (FE‐SEM). The building blocks (primary nanocrystals) of the spherical aggregates could be effectively tuned by adding different amount of urea. Furthermore, N₂ adsorption/desorption experiment displays a gradual increase of BET surface areas of spherical aggregates with increasing the amount of urea. Finally, the formation mechanism of CeO₂ spherical aggregates was preliminarily discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐template hydrothermal synthesis ZnS microspheres

Zinc sulfide (ZnS) microspheres were synthesized by a self‐template hydrothermal route using thiourea as sulphur source. The formation of these hollow spheres was mainly attributed to the oriented aggregation of ZnS nanocystals around the gas‐liquid interface between gas (H₂S, NH₃, or CO₂) and water followed by an Ostwald ripening process. The gas bubbles of H₂S, NH₃, or CO₂ produced during the reaction might play a soft‐template to form ZnS hollow microspheres. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron diffraction (ED), and photoluminescence (PL). The crystal structure of prepared ZnS microspheres is hexagonal phase polycrystalline. The average microspheres diameter is 1.5 ‐ 6 µm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of bamboo‐like SiC whiskers from waste silica fume

A process for the utilization of wasted silica fume is proposed in this work. Silicon carbide (SiC) whiskers several tens of micrometers in length and with a bamboo‐like morphology have been successfully synthesized by a carbothermal reduction process using purified silica fume as the silicon source. The morphology and structure of SiC whiskers were investigated by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and high‐resolution transmission electron microscopy. Studies found that the as‐synthesized whiskers were grown as single‐crystalline β‐SiC along the (111) growth direction. The whiskers consisted of hexagonal stems randomly decorated with larger‐diameter knots along their whole length. On the basis of the characterization results, a vapor–solid process was discussed as a possible growth mechanism of the β‐SiC whiskers.     

Hydrothermal synthesis of anatase flower‐like nanostructures for photocatalytic degradation of dye

Flower‐like hierarchical nanostructures of titanium dioxide (TiO₂) have been synthesized in large scale by a facile and controlled hydrothermal and after annealing process. The morphologies of flower‐like hierarchical nanostructures are formed by self‐organization of several tens of radially distributed thin flakes with a thickness of several nanometers holding a larger surface area. The materials are characterized by Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). The ultraviolet photocatalytic degradation of R6G dyes has been studied over this flower‐like hierarchical nanostructures and the activity is compared with that of commercial P25 TiO₂ under same conditions. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rapid synthesis of dendrite‐ and platelet‐like α‐Fe2O3 via a hydrothermal oxidation route

Dendrite and platelet‐like α‐Fe₂O₃ microcrystals were synthesized by the oxidation reaction of K₄Fe(CN)₆and NaClO₃ through a simple hydrothermal method. The structures and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experiment results show that NaOH played an important role in controlling the morphology of the final products. The possible mechanism was discussed to elucidate the formation of different morphologies of the α‐Fe₂O₃ microstructures. Besides, the magnetic property of the dendrite α‐Fe₂O₃ microstructure was characterized by a vibrating sample magnetometer (VSM). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of shuttle‐like Sb2S3 nanorod‐bundles via a solvothermal approach under alkaline condition

Uniform shuttle‐like Sb₂S₃ nanorod‐bundles were synthesized via a polyvinylpyrrolidone (PVP) assisted solvothermal approach under alkaline condition, using antimony chloride (SbCl₃) and thiourea (CH₄N₂S, Tu) as the starting materials in ethanol. The phase structure, composition and morphology of the product were characterized by means of X‐ray diffraction (XRD), energy dispersive X‐ray spectrometry (EDS), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy (HRTEM). XRD and EDS results confirm that the synthesized Sb₂S₃ nanorod‐bundles have an orthorhombic structure and an atomic ratio of 3:2 for S:Sb. TEM and HRTEM results show that the shuttle‐like Sb₂S₃ bundles are composed of nanorods with a size distribution of 20‐40 nm and growing along c‐axis. Furthermore, experiments under different reaction conditions were carried out and the mechanism for the growth of nanorod‐bundles was discussed (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TEM investigation of precipitates in VCz GaAs crystals

Bulk GaAs crystals were grown from various Ga‐rich melts by the vapour‐pressure controlled Czochralski method in order to reduce As precipitates. The correlation of the melt composition with both, structural perfection and solid composition was examined by various methods of transmission electron microscopy (TEM). From transmission electron diffraction and diffraction contrast imaging a direct correlation between melt composition and sample properties is missing. High‐resolution TEM imaging hints to inhomogeneities only for the sample grown from a melt with a mole fraction of y = 0.492. Strain analysis of a selected defect reveals a strained crystal lattice in the surrounding of the defect. For the same sample, high angle annular dark‐field imaging and energy dispersive X‐ray spectroscopy verify the formation of precipitates. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Misleading fringes in TEM images and diffraction patterns of Si nanocrystallites

High‐resolution transmission electron microscopy (HRTEM) images and electron diffraction patterns of twinned Si nanocrystallites were recorded along various directions and analyzed in detail. We point out that special attention must be paid when interpreting HRTEM images and diffraction patterns of twinned Si nanocrystallites, because elongation of reciprocal lattice points could fabricate misleading fringes and patterns. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

α‐Fe2O3 nanospindles loaded with ZnO nanocrystals: Synthesis and improved gas sensing performance

ZnO/α‐Fe₂O₃ nanocomposites were fabricated through a two‐step hydrothermal method. The morphology and composition of the as‐synthesized products were characterized by X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The gas sensing properties of the fabricated products were investigated towards ethanol, acetone, propanol, isopropanol, formaldehyde, chloroform and so on. The results demonstrated that the ZnO/α‐Fe₂O₃ nanocomposites exhibited excellent sensing properties and showed remarkably higher sensing responses and much lower optimum operating temperature compared to individual ZnO and α‐Fe₂O₃. In addition, the ZnO/α‐Fe₂O₃ nanocomposites have some selectivity for ethanol, propanol and isopropanol. The possible gas sensing mechanism was also proposed. Our studies demonstrate that our fabricated materials could be widely used in the future.     

Synthesis and properties of α‐Fe2O3 nanorods

We report synthesis of α‐Fe₂O₃ (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α‐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 α‐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)