Preparation,characterization and photoluminescence properties of ultra long SiC/SiO<Subscript>x</Subscript> nanocables

SiC core and SiO_x shell nanocables of a few millimeters long have been prepared by pyrolysis of SiO₂ nanopowder added poly(dimethyl siloxane) without catalyst in a tube furnace at 1050 °C in Ar. The influence of the synthesis conditions (synthesis temperature and cooling time) on the products is studied. The products obtained from different conditions are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy equipped with energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The results show that the cores and the shells are crystalline and amorphous, respectively, and that the addition of SiO₂ nanopowder and prolongation of cooling time both increase the diameter of the cores. The growth process of the nanocables is discussed. The photoluminescence emission bands of the nanocables are mainly from their shells. PACS 68.37.Hk; 68.37.Lp; 78.67.n; 81.07.b; 81.16.Be     

Synthesis and characterization of ZnO thin films by thermal evaporation

ZnO thin films have been successfully synthesized by thermal evaporation of pure zinc at 900 °C under the flow of different percentages of argon and oxygen gases. The films were characterized by X-ray diffraction (XRD), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis spectroscopy. The aim of this paper is to study the influence of the oxygen percentage on the structural and morphological properties of the ZnO films. VPSEM results show that very thick needle structures were produced at high oxygen percentages. EDS results revealed that only Zn and O are present in the sample, indicating a composition of pure ZnO. XRD results showed that the ZnO synthesized under different quantities of oxygen were crystalline with the hexagonal wurtzite structure. UV–vis spectroscopy results indicated that the optical band gap energies from the transmission spectrum are between 3.62 and 3.69 eV for ZnO thin films.     

Microemulsion-directed synthesis of different CuS nanocrystals

Through a microemulsion-directed route, CuS nanoparticles, nanorods, nanowires and tube-like structures were prepared while different quantities of surfactant were used. The arrangement of the microemulsion vesicles directed the growth behavior of the nanocrystals. Transmission electron microscopy (TEM) was used to investigate the different morphology of the as-synthesized products. X-ray powder diffraction (XRD) and electron diffraction (ED) were applied to characterize the properties of the products obtained. The mechanism of the nanocrystals with different shapes is discussed.     

Coaxial ZnO/SiO<Subscript>2</Subscript> nanocables fabricated by thermal evaporation/oxidation

ZnO/SiO₂ coaxial nanocables have been synthesized on silicon substrates by simply evaporating zinc powder under an argon and argon/oxygen mixed atmosphere sequentially. The diameters of these nanocables vary from 50 to 100 nm and the lengths up to several millimeters. Electron microscopy and chemical composition investigations reveal that the nanocable consists of a crystalline ZnO core surrounded by an amorphous silica sheath. The electron diffraction pattern proves that the long-axis direction of ZnO cores grows along the [0001] direction. Silica nanotubes with wall structures have been obtained by the selective dissolution of the cores with hydrochloric acid. PACS 81.10.Bk; 81.05.Hd     

Synthesis and characterization of CdS nanoparticles in the presence of oleic acid as solvent and stabilizer

Oleic acid (OA)-capped CdS nanoparticles (NPs) have been successfully synthesized via the direct reaction of Cd(CH₂COO)₂·2H₂O with S powder in OA solvent at 230 °C under nitrogen flow, which was a kind of clean and air-stable solvent. The morphologies and structures of the as-synthesized CdS NPs are examined by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectroscopy, and the typical Ostwald ripening growth mechanism is concluded. Moreover, the collected ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy demonstrate good optical properties of CdS NPs.     

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     

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.     

Structural and optical properties of chemically synthesized monodispersed CdCr2S4 films

Alkaline chemical synthesis of amorphous CdCr₂S₄ (CCS) thin films of different thicknesses using cadmium chloride, chromic acid, disodium salt of ethylenediaminetetra acetic acid and thiourea precursors is reported, and the structural and surface morphological properties of CCS using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques are discussed. Films of aggregated grains with some void spaces are obtained. Change in band gap energy and electrical resistivity of CCS films are discussed as a function of film thickness. n-type conductivity is confirmed from the sign of thermally generated voltage across the cold and hot junctions.     

Structures and properties of the polyacrylonitrile fabric coated with ZnO-Ag composites

The polyacrylonitrile (PAN) fabric coated with ZnO-Ag composite was achieved by hydrothermal synthesis techniques and photochemical method. The PAN fabrics coated with ZnO-Ag composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV-vis spectrophotometer and fabric induced static tester, respectively. The SEM images revealed the formation of the coating aggregates on the fiber surface. The FT-IR spectra and XRD patterns revealed the chemical structures of the coatings on the PAN fabrics. The results of UV-vis test showed that there was an obvious increase in ultraviolet resistant properties after coating. The antistatic properties results revealed the improvement in the antistatic performance of coated fabrics, attributed to the superior electrical and optical properties of ZnO and Ag.     

Surface functionalisation of polymer nanofibres by sputter coating of titanium dioxide

The surface properties of nanofibres are of importance in various applications. In this work, electrospun polyamide nanofibres were used as substrates for creating functional nanostructures on the nanofibre surfaces. A RF magnetron sputter coating was used to deposit the functional layer of titanium dioxide (TiO₂) onto the nanofibres. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and environmental scanning electron microscopy (ESEM) were employed to study the topography, grain structure and wetting of the nanofibre surfaces, respectively. The AFM results indicated a significant difference in the morphology of the nanofibres before and after the TiO₂ sputter coating. The XRD analysis showed the amorphous structures of the TiO₂ deposition layer. XPS spectra reflected the chemical features of the deposited nanostructures. The ESEM observation revealed that the surface wettability of TiO₂ sputter coated nanofibres was significantly improved after UV irradiation.     

ZnO-coated zinc antimonate nanocables

ZnO-coated zinc antimonate (ZnSb₂O₄) nanocables have been fabricated via a simple one-step thermal evaporation of layered powders of Sb₂O₃ and ZnO on a brass substrate. The samples were characterized using X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy with a high-angle annular dark-field attachment. The nanocables are several tens of micrometers in length; the ZnSb₂O₄ core is ∼30 nm in diameter and the thickness of the ZnO sheath is ∼5 nm. Both the ZnSb₂O₄ core and the ZnO sheath are single crystalline. The controlled growth mechanism of ZnO-coated ZnSb₂O₄ nanocables was considered to be the combination of oxide-assisted evaporation and vapor–solid processes. PACS 61.46.+w; 81.07.-b     

Catalytic synthesis of single-crystalline gallium nitride nanobelts

Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed.     

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.     

Morphology controlled solvothermal synthesis of Cd(OH)2 and CdO micro/nanocrystals on Cd foil

Cadmium hydroxide (Cd(OH)₂) and cadmium oxide (CdO) nano and micro crystals were synthesized in ethanol-water medium using cadmium foil both as a source and substrate under solvothermal condition. Different concentrations of ammonium hydroxide, hydrazine hydrate, sodium hydroxide and potassium hydroxide were added to study the structural and morphological variations in the products. Synthesis was carried out at different temperatures to study the growth stages of the nano/microstructures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The as-prepared Cd(OH)₂ products were transformed to CdO by thermal treatment in air. The possible growth mechanism for the formation of different morphologies at different basic medium has been proposed. The optical absorption measurement was carried out to determine the values of the band gap of CdO.     

Synthesis, morphologies and Raman-scattering spectra of crystalline stannic oxide nanowires

SnO₂ nanowires were synthesized using a direct gas reaction route and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman-scattering spectroscopy. XRD, SEM, SAED and HRTEM indicated that the products were tetragonal SnO₂ nanowires with diameters of 10–50 nm. The nanowires were single crystal and solid inside. Dendritic nanowires were observed for the first time. Three vibrational modes were observed in the Raman spectra of the samples. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 19 July 2002     

Fabrication of bamboo-shaped GaN nanorods

Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated that the nanorods were single-crystal wurtzite GaN. Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001     

Effect of high energy ion irradiation on silicon substrate in a pulsed plasma device

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si(1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are reported. In particular, it has been found that with silicon targets, the application of PF carbon ion beams results in the formation of a surface layer of hexagonal (6H) silicon carbide, with embedded self-organized step/terrace structures.     

Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O3 films obtained by pulsed laser deposition

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance.     

Centimetre-Long Single Crystalline ZnO Fibres Prepared by Vapour Transportation

Centimetre-long ZnO fibres are synthesized by vapour transportation via thermal evaporation of ZnO powders. The growth process is carried out in a graphite crucible, in which ZnO powder is loaded as the source material, and a silicon wafer is positioned on the top of the crucible as the growth substrate. During the growth process, the source temperature is kept at 800℃ and the substrate temperature is kept at 600℃. Typical growth time to obtain centimetre-long ZnO fibres is 5-10 hours. Scanning electron microscopy （SEM）, x-ray diffraction （XRD）, transmission electron microscopy （TEM）, and selected area electron diffraction （SAED） measurement results show that ZnO fibres are single crystalline with high crystalline quality and very low defects concentration.     

Growth and Characterization of Trumpet-Shaped ZnO Microtube Arrays on Si Substrates

Aligned trumpet-shaped zinc oxide microtube arrays have been successfully prepared on silicon （100） substrates via the chemical vapour deposition method with a mixture of ZnO and active carbon powders as reactants. The results show that two types of trumpet-shaped ZnO microtubes can be obtained. A plausible growth mechanism based on the studies of scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, x-ray diffraction （XRD）, and room-temperature photoluminescence spectroscopy is proposed and discussed. The initial metastable zinc-rich ZnOx embryos play a key role in the formation of trumpet-shaped ZnO microtubes. On the different surfaces of metastable zinc-rich ZnOx （x 〈 1）, embryos exhibit different stabilities and resistivities to oxidation; these tiny embryos are gradually extended with different growing rates along the directions of its long axis and circular boundary around its oxide shell. Just this special reason creates the formation of trumpet-shaped microtubes and results in the inerratic and imperfect hexagonshaped cross section that appears. Moreover, the analytical results also show that the as-synthesized ZnO microtube arrays can exhibit better room-temperature photoluminescence behaviour.