Synthesis and characterization of dentate-shaped β -Ga2O3 nano/microbelts via a simple method

Dentate-shaped β-Ga₂O₃ nano/microbelts were synthesized successfully via chemical vapor deposition without any other reaction or catalyzer material. The morphology and crystal structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analytic technologies, respectively. The growth mechanism of the products was discussed assisted by the SEM and TEM images. The photoluminescence properties of the β-Ga₂O₃ nano/microbelts have been investigated with a He–Cd laser (325 nm) at room temperature. PACS 81.05.Hd; 81.07.Bc; 81.10.Bk; 81.15.Gh; 81.70.Fy     

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg     

Synthesis of aligned GaN nanorods on Si (111) by molecular beam epitaxy

Straight and well-aligned GaN nanorods have been successfully synthesized by molecular beam epitaxy (MBE) method. The GaN nanorods have been characterized by field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). SEM images show that GaN nanorods are constituted with two parts of which shapes are different from each other. The upper part of the nanorod is very thin and its lower part is relatively thick. The XRD and EDS analysis have identified that the nanorods are pure hexagonal GaN with single crystalline wurtzite structure. The TEM images indicate that the nanorods are well crystallized and nearly free from defects. The XRD, HRTEM, and SAED pattern reveal that the growth direction of GaN nanorods is 〈0001〉. The photoluminescence (PL) spectra indicate the good emission property for the nanorods. Finally, we have demonstrated about the two-step growth of the nanorods. PACS 81.07.Bc; 81.05.Ea; 81.15.Hi     

Sol–gel electrophoretic deposition and optical properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowire arrays

Ordered Fe₂O₃ nanowire arrays embedded in anodic alumina membranes have been fabricated by Sol–gel electrophoretic deposition. After annealing at 600 °C, the Fe₂O₃ nanowire arrays were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD). SEM and TEM images show that these nanowires are dense, continuous and arranged roughly parallel to one another. XRD and SAED analysis together indicate that these Fe₂O₃ nanowires crystallize with a polycrystalline corundum structure. The optical absorption band edge of Fe₂O₃ nanowire arrays exhibits a blue shift with respect of that of the bulk Fe₂O₃ owing to the quantum size effect. PACS 78.67.Lt; 81.05.Je; 81.07.Vb     

From Ore to Tool – Iron Age Iron Smelting in the Largest and Oldest Meteorite Crater in the World

The Vredefort Impact Structure in South Africa is the biggest and oldest remnant meteorite impact crater in the world where various ancient cultures thrived. In this paper some light will be shed on the Iron Age, iron smelting aspects of the people that inhabited the area and the results of a laboratory study of iron artefacts and a possible source of iron ore in the region is given. A sectional piece from a hoe manufactured in a small bloomery furnace was polished and etched and subsequently analyses with SEM and Mössbauer techniques were obtained. The hoe has a typical cast iron composition (2.9% C, 0.1% Mn, 0.4% Si, 0.4% P and 96.2% Fe, all wt.%) and contains many slag inclusions with wustite dendrites. The Mössbauer spectrum consisted of iron (86%), wustite (5%) and oxihydroxide (9%) and the thin (200 μm) corrosion layer consisted of hematite (55%) and oxihydroxides (45%). At a furnace site, various slag clumps (26.3% C, 24.8% SiO₂, 11.3% Al₂O₃, 1.3% P₂O₅, 1.0% K₂O, 0.4% CaO and 30.2 FeO, all wt.%, average of four samples) and iron nodules (7.6% C, 6.0% Mn, 4.3% Si, 1.4% Al, 80.7% Fe, all wt.%) were found. The Mössbauer spectrum of the slag consisted of iron (7%), magnetite (56%), fayalite (2%) and oxihydroxides (35%) and that of the iron nodules yielded iron (28%), wustite (12%), magnetite (20%) and oxihydroxides (40%). A possible ore source containing 84% FeO, 7% of Al₂O₃ and SiO₂ (all in wt.%) and minor impurities is located a few kilometers from the furnace site, yielding a Mössbauer spectrum consisting of hematite (70%) and oxihydroxides (30%).     

紫外光固化聚丙烯酰/SiO2有机/无机杂化气凝胶制备

 采用自制的甲基丙烯酰多羟基倍半硅氧烷制备了UV固化的有机/无机杂化湿凝胶。湿凝胶经CO₂超临界干燥后即得到相应的杂化气凝胶,气凝胶经场发射扫描电子显微镜,高分辨透射电镜分析表明：构成气凝胶3维珍珠链结构的骨架的颗粒尺寸为20～30 nm,骨架上具有5～10 nm的孔洞结构,骨架颗粒有机、无机组分间没有明显的相界面。气凝胶的比表面积、吸附特性和微观孔结构采用经典的N₂吸附法获得,结果表明气凝胶比表面积为520.9 m²/g,孔洞结构主要由50 nm以下的介孔所构成。     

Selective growth of carbon nantoubes on SiO2/Si substrate

Three-step raising temperature process was employed to fabricate carbon nanotubes by pyrolysis of ferrocene/melamine mixtures on silica and single crystalline silicon wafers respectively. Then the morphologies, structures and compositions of obtained carbon nanotubes are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscope (EDX) and electron energy-loss spectroscopy (EELS). TEM and SEM observation shows that on silica substrate, high-oriented carbon nanotube can grow compactly to form continuous film on both frontal and cross-section surfaces, but on silicon substrate, only can form on cross-section surface. These carbon nanotubes have much irregular cup-like structure, and with outer diameter varying from 25 nm to 35 nm. At the top end of carbon nanotube there is a catalyst particle. EDX analysis reveals that the particle are iron cluster, and EELS spectrum indicates that the nanotube is composed of pure carbon. Finally, the effect of substrate surface roughness on the growth behavior of carbon nanotubes has been discussed.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

Role of Cr ions on superexchange coupling in α-Fe2O3 nanoparticles

Synthesis of nanocomposites of iron oxide & chromium oxide (α-Fe₂O₃–Cr₂O₃) with different concentrations was carried out by a wet-chemical method and the structural, optical and hyperfine properties have been investigated. The prepared nanocomposites were characterized by powder X-ray diffractometry (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–VIS spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and Mössbauer spectroscopy. XRD measurements confirmed the formation of pure phase composites having particle sizes in nanometer regime. The same has been corroborated by TEM micrographs, which revealed that the formation of monodispersed nanocomposites have the average particle size 44 nm. Mössbauer study of the samples showed the transition of iron oxide from anti-ferromagnetic state to paramagnetic state having a typical relaxation in the spectrum with increasing concentration of Cr₂O₃.     

Preparation of flower-like and rod-like boehmite via a hydrothermal route in a buffer solution

Flower-like and rod-like boehmite has been synthesized using a hydrothermal route in a buffer solution. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR). The SEM and the TEM images of products obtained after different processing times reveal that the buffer solution plays an important role in the rod-like boehmite formation. This approach may allow us to have a better control of the size and morphology of the crystalline boehmite. And the surface area of boehmite hollow microspheres was calculated using Brunauer-Emmett-Teller (BET) model. The possible formation mechanism was proposed and discussed.     

A convenient ultrasonic irradiation technique for in situ synthesis of zinc sulfide nanocrystallites at room temperature

Nanocrystalline ZnS has been synthesized using a sonochemical reaction of a mixed solution of Zn(NO₃)₂, Na₂S₂O₃ and (CH₃)₂(OH)CH in Ar under ambient conditions. Detailed investigations with X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) are reported. It was found that phase-pure ZnS nanocrystallites were produced, and the ZnS nanoparticles were about 6.5 nm in size, as indicated by TEM observation. The chemical mechanism for the formation of ZnS nanocrystals is discussed. This convenient method is found to be an efficient way to produce other chalcogenides as well. PACS 81.05.Dz; 81.05.Ys; 81.20.Zx     

Characterization for metamaterials with a high refractive index formed by periodic stratified metallic wires array

Ultralong ZnO nanowires were successfully prepared on a large scale by a microwave-assisted aqueous route without using any surfactant or template at relatively low temperature of 120°C. The obtained nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectrum (EDX). The growth mechanism and photoluminescence of the one-dimensional nanostructure, and photovoltaic performances for dye-sensitized solar cell (DSSC) of the nanowires were discussed in detail.     

X-ray and electron microscopy of actinide materials

Actinide materials demonstrate a wide variety of interesting physical properties in both bulk and nanoscale form. To better understand these materials, a broad array of microscopy techniques have been employed, including transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDXS), high-angle annular dark-field imaging (HAADF), scanning electron microscopy (SEM), wavelength dispersive X-ray spectroscopy (WDXS), electron back scattered diffraction (EBSD), scanning tunneling microscopy (STM), atomic force microscopy (AFM), and scanning transmission X-ray microscopy (STXM). Here these techniques will be reviewed, highlighting advances made in the physics, materials science, chemistry, and biology of actinide materials through microscopy. Construction of a spin-polarized TEM will be discussed, considering its potential for examining the nanoscale magnetic structure of actinides as well as broader materials and devices, such as those for computational magnetic memory.     

Green synthesis of ZnO nanoparticles in a room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Nanoparticles of ZnO with the wurtzite structure have been successfully synthesized via a microwave through the decomposition of zinc acetate dihydrate in an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, as a solvent. Fundamental characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were conducted for the ZnO nanostructures.To explore the growth mechanism, the samples have been prepared in different irradiation time and also cetyltrimethylammonium bromide (CTAB) has been used as the capping reagent.     

Preparation and characterization of oriented silica nanowires

Large-scale of oriented closely packed silica nanowire bunches have been synthesized by using large size (1-10 μm in diameter), low melting point tin droplets as catalyst on silicon wafers at 980 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that the amorphous silica nanowires have lengths of 50-100 μm and diameters of 100-200 nm. Unlike any previous observed results using high melting point metal (such as gold and iron) as catalyst, the Sn catalyst growth exhibits many interesting phenomena. Each Sn ball can simultaneously catalyze the growth of many silica nanowires, which is quite different from the conventional vapor-liquid-solid process.     

Scanning and transmission electron microscopy studies on a model series of spherulitic segmented polyurethanes

Scanning (SEM) and transmission (TEM) electron microscopy studies were made on a model series of four segmented polyurethanes. The morphologies of both the homopolymers and of their mixtures were made by SEM while TEM was utilized to study only ultrathin films of the homopolymers. It was found that well-structured spherulitic morphologies could be induced in these systems and their mixtures, and that control over the textures could be maintained by solution casting conditions. The domains were observable via TEM, and the general orientation of this structure within the spherulites was noted. Deformation studies of the spherulitic textures were followed by both SEM and small-angle light scattering. It was concluded that, in general, the spherulites deform in a nonaffine manner–this is particularly true for the systems possessing a porous texture.     

Solid state synthesis and room temperature magnetic properties of iron phosphide nanoparticles

Room temperature magnetic properties have been achieved for nano-crystalline iron phosphide synthesized from the direct solid state reaction of iron chloride and tri-octylphosphine (TOP). The magnetization continuously increased with higher magnetic fields, indicating a super-paramagnetic behavior. It is observed that room temperature magnetism is possible for the material showing antiferromagnetic nature at low temperatures. In the present synthesis, TOP acted as a source of phosphorus as well as a surfactant. X-ray diffraction (XRD) studies revealed that the black powder is a mixture of FeP and Fe₂P. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed elongated as well spherical particles. Energy dispersion X-ray analysis (EDAX) confirmed a non-stoichiometric iron phosphide. Presence of TOP was confirmed by infra-red (IR) spectroscopy, and thermo-gravimetric analysis (TGA) indicated about 6% wt. loss due to presence of organics.     

Effect of ultrasonic treatment on the morphology of casein particles

In this study, the effect of ultrasonic treatment duration on the morphology of self-assembled casein particles was investigated by atomic force microscopy (AFM), low vacuum scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the case of AFM images, the particle analysis which was carried out by the SPIP program showed that the self-assembled casein particles after being ultrasonically treated for 2 min got smaller in size compared to the casein particles that have not been exposed to any ultrasonic treatment. Surprisingly, however, increasing the ultrasonic time exposure of the particles resulted in an opposite effect where larger particles or aggregates seemed to be present. We show that by comparing the results obtained by AFM, SEM and TEM, the information extracted from the AFM images and analyzed by SPIP program give more detailed insights into particle sizes and morphology at the molecular level compared to SEM and TEM images, respectively.     

Synthesis and characterization of GaP nanochains with a twin-modulated quasi-periodic structure

GaP nanochains have been synthesized by hydrogen-assisted thermal evaporation, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. GaP nanochains possess a (111) twin crystal plane-modulated quasi-periodic structure, that gives a strong green photoluminescence at 618 nm. While the Raman spectrum of the nanochains is similar to that of the GaP crystal, the intensity of the longitudinal optical (LO) peak is stronger than that of the transverse optical (TO) peak, which is supposedly related to the nanochain microstructures.     

The synthesis of highly oriented GaN nanowire arrays

Highly oriented GaN nanowire arrays have been achieved by the catalytic reaction of gallium with ammonium. The resulting materials were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). SEM images show that the resulting materials are nanowire arrays with a uniform length of about 10 μm. XRD, EDS, TEM and SAED indicate that the nanowire arrays are single-crystal hexagonal GaN with a wurtzite structure. They have diameters of 10 to 20 nm. Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: wwwangjc@sina.com