Synthesis and red-shifted photoluminescence of single-crystalline ZnO nanowires

Local-oriented single-crystalline ZnO nanowires have been synthesized in large scale by a simple microemulsion method in the presence of sulfonate-polystyrene (S-PS) and dodecyl benzene sulfonic acid sodium salt (DBS). The as-prepared product is characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), infrared (IR) spectra and photoluminescence (PL) spectrum. The nanowires exhibit a local congregation and preferentially grow along the [0 0 2] facet. FT-IR spectrum indicates that S-PS is adsorbed on the surface of ZnO nanowires. The PL spectrum shows evidently red-shifted ultraviolet (UV) emission.     

Two-step synthesis of one-dimensional single crystalline GaN nanowires

Straight and smooth GaN nanowires were synthesized on quartz substrates through the direct reaction of Ga₂O₃ thin films with flowing ammonia in a horizontal oven without using a template or catalyst. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM) and photoluminescence (PL) were used to characterize the samples. The straight and smooth cylindrical nanostructures are high quality single crystalline hexagonal wurtzite GaN nanowires with diameters ranging from 5 to 30 nm and lengths up to 20 μm. The near-band-edge emission peak located at 367 nm was observed at room temperature.     

The structure and photoluminescence properties of TiO<Subscript>2</Subscript>-coated ZnS nanowires

The structure and photoluminescence properties of TiO₂-coated ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO₂ by using the metal organic chemical vapor deposition (MOCVD) technique. We performed scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, and photoluminescence (PL) spectroscopy to characterize the as-synthesized and TiO₂-coated ZnS nanowires. TEM and XRD analyses revealed that the ZnS core and the TiO₂ coatings had crystalline zinc blende and crystalline anatase structures, respectively. PL measurement at room temperature showed that the as-synthesized ZnS nanowires had two emissions: a blue emission centered in the range from 430 to 440 nm and a green emission at around 515 nm. The green emission was found to be dominant in the ZnS nanowires coated with TiO₂ by MOCVD at 350°C for one or more hours, while the blue emission was dominant in the as-synthesized ZnS nanowires. Also the mechanisms of the emissions were discussed.     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Well-aligned ZnO nanowires grown on Si substrate via metal–organic chemical vapor deposition

ZnO nanowires were grown on silicon substrate by metal–organic chemical vapor deposition (MOCVD) without catalysts. The scanning electron microscopy (SEM) observations along with X-ray diffraction (XRD) results suggest that the ZnO nanowires are single crystals vertically well-aligned to silicon substrate. Room-temperature photoluminescence (PL) measurement reveals strong UV emission and weak green emission, which demonstrates that the nanowires are of good optical properties. The mechanism of the catalyst-free growth of ZnO nanowires on silicon substrate is proposed.     

Fabrication and structural properties of LaFeO3 nanowires by an ethanol–ammonia-based sol–gel template route

Highly ordered LaFeO₃ nanowire arrays of composite oxides were synthesized within porous anodic aluminum oxide (AAO) templates by an ethanol–ammonia-based sol–gel route. The results of scanning electron microscopy and transmission electron microscopy revealed that the obtained LaFeO₃ nanowires had a uniform length and diameter, which were determined by the thickness and the pore diameter of the applied AAO template. Energy-dispersive X-ray spectroscopy demonstrated that the stoichiometric LaFeO₃ was formed. Furthermore, the results of X-ray diffraction and selected-area electron diffraction indicated that the LaFeO₃ nanowires had a perovskite-type crystalline structure. It is expected that the novel and effective technique presented in this article would also be appropriate for the preparation of nanowires of other mono-component or multi-component oxides. PACS 61.66.Fn; 61.46.+w; 81.20.Fw     

Synthesis of In-doped Ga2O3 zigzag-shaped nanowires and optical properties

In-doped Ga₂O₃ zigzag-shaped nanowires and undoped Ga₂O₃ nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In₂O₃ and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

Synthesis and characterization of GaN nanowires by ammoniating Ga2O3/Cr thin films deposited on Si(1 1 1) substrates

GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30-80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.     

Synthesis and characterization of PbS nanorods and nanowires

 A surfactant assisted solvotermal approach for the controllable synthesis of PbS nanowires and nanorods is applied. The synthesis is based on decomposition of lead thiocyanate in boiling benzyl alcohol with Cetyl trimethyl ammonium bromide used as a surfactant. Nanowires of PbS (about 2–3 μm with an average diameter of 30–50 nm) and nanorods (200–300 nm in length with an axial ratio of 4–5) were synthesised. The nanostructures were characterized by high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and X-ray diffraction analysis. The experimental results indicate that the reaction duration and concentration of surfactant play key roles in determining the final morphologies of PbS blocks building and also in their crystallinity. A possible mechanism for creation of PbS nanowires and nanorods is discussed.     

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.     

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     

Synthesis and characterization of the SnS nanowires via chemical vapor deposition

Single-crystal SnS nanowires have been successfully synthesized by catalysis-assistant chemical vapor deposition. Applying Au nanoparticles which were applied on the ITO surface as the catalysator, using SnS powder and S powder as precursors and the Ar+H₂ mixed atmosphere as the shielding and carrier gas, the SnS nanowires were obtained. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and Raman spectroscopy were employed to characterize the as-synthesized SnS nanostructures. The room-temperature photoluminescence properties of these as-prepared SnS nanowires were presented.     

Preparation and characterization of the transparent nanocomposite mirror film for the infrared region by sol–gel method

Transparent mirror coated, SiO₂–Ag/PV P nanocomposites were prepared on the Pyrex glass slides by dip-coating technique. Embedding of the silver (Ag) nanoparticles on silica modified polyvinyl pyrrolidone (PVP) was performed by the sol–gel method. As prepared transparent mirror coated SiO₂–Ag/PV P nanocomposite films were finally characterized for surface morphology, chemistry, and nano size dimensions using various advanced analytical techniques including, UV visible, Fourier transform, infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), dispersive x-ray analaysis (EDAX) and transmission electron microscopy (TEM) analysis. It was found that all the prepared samples were almost uniform particles of Ag nanospheres of 7–8 nm diameters arranged as double paralleled nanowires with an average length of 200–450 nm and diameters of around 20–25 nm.     

Catalyst-free synthesis of GeO2 nanowires using the thermal heating of Ge powders

Germanium dioxide (GeO₂) nanowires have been synthesized by means of the simple evaporation of solid Ge powders, without using metal catalysts. The nanowires, with a diameter of about 90–200 nm, were characterized using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The obtained GeO₂ nanowires were crystalline with a hexagonal structure. The growth mechanism was discussed with respect to the vapor–solid process. The photoluminescence measurement revealed two emission peaks at about 2.45 eV and 2.91 eV at room temperature, opening up a route to potential applications in future optoelectronic nanodevices. Raman measurement of as-synthesized GeO₂ nanowires was made at room temperature.     

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     

Temperature-controlled growth and photoluminescence of AlN nanowires

By varying the substrate temperature in the range of 800-1000 °C, the conditions for the synthesis of AlN nanowires were optimized. Al powders were heated under flowing ammonia gas. The samples were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. Based on the absence of tip particles, the growth mechanism of AlN nanowires was considered to follow a vapor-solid process. The overall intensity of the PL spectra was increased by increasing the synthesis temperature, whereas their shapes were changed by varying the synthesis temperature. The associated emission mechanisms are discussed.     

Sol–gel template synthesis and characterization of LaCoO3 nanowires

Densely packed LaCoO₃ nanowires of the rare-earth perovskite-type composite oxide were synthesized within a porous anodic aluminum oxide (AAO) template by means of the sol–gel method using nitrate as raw the material and citric acid as the chelating agent. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the LaCoO₃ nanowires possessed a uniform length and diameter, which were controlled by the thickness and the pore diameter of the applied AAO template, respectively. The results of X-ray diffraction (XRD) and the selected area electron diffraction (SAED) indicated that the LaCoO₃ nanowires had a rhombohedral perovskite-type crystal structure. Furthermore, X-ray photoelectron spectroscopy (XPS) demonstrated that LaCoO₃ nanowires were formed. Finally, the formation mechanism of nanowires was also discussed. PACS 61.66.Fn; 61.46.-W; 81.20.Fw     

硫掺杂ZnO纳米线的电化学制备及发光特性

"采用电场辅助电化学沉积法,利用阳极氧化铝模板模板制备了高度择优取向的硫掺杂ZnO单晶纳米线．X射线衍射仪、隧道电子显微镜、选取电子衍射对所得样品的结构、形貌分析表明,所得纳米线是沿(101)择优取向的六方纤锌矿结构单晶纳米线,长约几十微米、平均直径约70 nm. X射线光电子能谱对化学组成的分析进一步证实掺杂硫原子的存在．用荧光光谱仪(PL)对S掺杂前后的ZnO纳米线进行光学特性测量发现,S掺杂较大地改变了ZnO纳米线的发光性质．在PL谱中,除了有典型的ZnO纳米线在378、392 nm处的强紫外发光峰     

Growth of single-crystal magnetite nanowires from Fe3O4 nanoparticles in a surfactant-free hydrothermal process

Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe₃O₄. A mechanism for nanowire growth is proposed.     

Electrochemical deposition and characterization of Cu2O nanowires

Cu₂O nanowires were successfully synthesized by an electrochemical method using an alumina membrane as template through precise control of the pH value of the electrolyte. The deposition process was monitored by the time–current curve. Characterization was performed by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The growth directions of the Cu₂O nanowires were determined and the possible growth mechanism is discussed. PACS 68.37.Lp; 81.07.-b; 81.16.Be