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     

Influence of the solvent on ultrasonically produced SbSI nanowires

The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2₁ (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.     

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.     

Synthesis and characterization of GaN nanowires

In this work, GaN nanowires were fabricated on Si substrates coated with NiCl₂ thin films using chemical vapor deposition (CVD) method by evaporating Ga₂O₃ powder at 1100 °C in ammonia gas flow. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM) and photoluminescence (PL) spectrum are used to characterize the samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanowires is also discussed.     

A facile route to synthesize titanium oxide nanowires via water-assisted chemical vapor deposition

Single crystalline rutile titanium oxide nanowires have been synthesized in bulk yield based on commercial metal titanium by a facile water-assisted chemical vapor deposition method. The morphology, crystallinity, and phase structure of the nanowires have been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). This growth strategy is applicable for commercial metal titanium substrate with different spatial dimensions, such as powder, network mesh, and flat foil. The as-synthesized nanowires are found to be mainly composed of single crystalline rutile TiO₂ nanowires in spiral shape with a small amount of hexagonal Ti₂O nanowires with zigzag form. A growth mechanism has been proposed to explain the novel spiral and zigzag types of titanium oxide nanowires under moderate temperature (850 °C). This method promises an alternative way for industrialization of titanium oxide nanowires which may serve as a good candidate for various industrial applications such as optoelectronic, electronic, and electrochemical nanodevices.     

Growth and morphologies of large-scale SnO2 nanowires, nanobelts and nanodendrites

Single-crystalline SnO₂ nanowires, nanobelts and nanodendrites were synthesized by a simple gas-reaction route on a large scale at 900 °C. They were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). FE-SEM images showed that the products consisted of nanowires, nanobelts and nanodendrites that represent a novel morphology reported for the first time. XRD, SAED and EDS indicated that they were single-crystalline tetragonal SnO₂. The influence of experimental conditions on the morphologies of the products is discussed. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: 86-10/82649531, E-mail: xlchen@aphy.iphy.ac.cn     

Elevated performances of SnS anodes with MWNTs as conductive agent for rechargeable lithium-ion batteries

SnS nanoparticles were mechanochemically synthesized and fabricated into electrodes with two kinds of conductive agents, acetylene black and multi-wall carbon nanotubes (MWNTs), respectively. The morphology and structure of as-synthesized SnS powder were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical properties of as-prepared electrodes were investigated by discharge–charge test, cyclic voltammogram, and electrochemical impedance spectrum. By comparing the variation of the charge-transfer impedance R _ct at different discharge states, it was found that the value of R _ct of the electrode with MWNTs as conductive agent was less than that of the electrode with acetylene black as conductive agent. The electrode with MWNTs as conductive agent had preferable cycling performances, which was believed to be attributed to the tenacity and good conductivity of MWNTs.     

Preparation, conversion, and comparison of the photocatalytic property of Cd(OH)2, CdO, CdS and CdSe

In this paper, we report the hydrothermal preparation of Cd(OH)₂ nanowires and further conversion to CdO nanobelts, CdS nanowires and CdSe nanoparticles through thermal treatment, solvothermal and mixed-solvothermal routes, respectively. The as-obtained products were characterized by means of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FEMSEM). Research showed that four cadmium compounds were good photocatalysts for the degradation of organic dyes such as Safranine T and Pyronine B, under irradiation of 365 nm UV light. The order of catalytic activity of different materials was found to be Cd(OH)₂<CdO<CdS<CdSe.     

Sonochemical preparation of SnS and SnS2 nano- and micropowders and their characterization

Sonochemical production of tin(II) and tin(IV) sulfides is investigated. Different conditions of syntheses are examined: used solvent (ethanol or ethylenediamine), source of tin (SnCl₂ or SnCl₄), the molar ratio of thioacetamide to the tin source, and time of sonication. The obtained powders are characterized by the X-ray diffraction method (PXRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and the Tauc method. Raman and FT-IR measurements were performed for the obtained samples, which additionally confirmed the crystallinity and phase composition of the samples. The influence of experimental conditions on composition (is it SnS or SnS₂), morphology, and on the bandgap of obtained products is elucidated. It was found that longer sonication times favor more crystalline product. Each of bandgaps is direct and most of them show typical values – c.a. 1.3 eV for SnS and 2.4 eV for SnS₂. However, there are some exceptions. Synthesized powders show a variety of forms such as needles, flower-like, rods, random agglomerates (SnS₂) and balls (SnS). Using ethanol as a solvent led to powders of SnS₂ independently of which tin chloride is used. Sonochemistry in ethylenediamine is more diverse: this solvent protects Sn²⁺ cations from oxidation so mostly SnS is obtained, while SnCl₄ does not produce powder of SnS₂ but Sn(SO₄)₂ instead or, at a higher ratio of thioacetamide to SnCl₄, green clear mixture.     

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.     

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.     

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.     

Large-scale synthesis of In2O3 nanowires

In₂O₃ nanowires have been successfully fabricated on a large scale from indium particles by thermal evaporation at 1030 °C. The as-synthesized products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM images show that these nanowires are uniform with diameters of about 60–120 nm and lengths of about 15–25 μm. XRD and selected-area electron diffraction analysis together indicate that these In₂O₃ nanowires crystallize in a cubic structure of the bixbyite Mn₂O₃ (I) type (also called the C-type rare-earth oxide structure). The growth mechanism of these nanowires is also discussed. Received: 29 June 2001 / Accepted: 28 September 2001 / Published online: 20 December 2001     

Preparation and characterization of electrodeposited SnS thin films

Tin sulfide (SnS) thin films have been deposited by electrodeposition using potentiostaic method on indium doped tin oxide (ITO) coated glass substrates from aqueous solution containing SnCl₂·2H₂O and Na₂S₂O₃ at various potentials. Good quality thin films were obtained at a cathodic potential −1000 mV versus saturated calomel electrode (SCE). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR). X-ray diffraction analysis shows that the crystal structure of SnS thin films is orthorhombic with preferential orientation along 〈0 2 1〉 plane. Microstructural parameters such as crystallite size, micro strain, and dislocation density are calculated and found to depend upon cathodic potentials. SEM studies reveal that the SnS films exhibited uniformly distributed grains over the entire surface of the substrate. The optical transmittance studies showed that the direct band gap of SnS is 1.1 eV. FTIR was used to further characterize the SnS films obtained at various potentials.     

Synthesis of quasi-1D cuprous oxide nanostructure and its structural characterizations

A wealth of superfine polycrystalline cuprous oxide (Cu₂O) nanowires have been synthesized with hydrazine hydrated (N₂H₄·H₂O), act as the reducing agent, and Cu(OH)₂ nanowires, act as a soft template and surfactant, at room temperature. Two methods were employed for the synthesis of these nanowires, i.e. with and without capping agent (polyethylene glycol Mw 8000). Techniques of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern, electron diffraction X-ray (EDX) spectroscopy, and UV-visible (UV-vis) spectroscopy have been used to characterize the morphology, structure, crystallinity, purity, and composition of nanowires. The average diameters of Cu₂O nanowires, prepared with and without capping agent, were observed to be 8-10 and 12-15 nm and lengths of several microns, respectively. It is found that capping agent (PEG) confines the dimensions of synthesized nanowires. In addition, the observed optical band gap of products show blue-shift effect compared to the bulk Cu₂O (E_g=2.17 eV), which ascribe it as a promising material for the conversion between solar energy and electrical or chemical energy.     

Synthesis of aligned gallium nitride nanowire quasi-arrays

Self-aligned GaN nanowire quasi-arrays were synthesized on MgO crystal through a simple gas reaction method. They were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy and high-resolution transmission electron microscopy (HRTEM). FE-SEMimages showed that the product consisted of quasi-arrays of nanowires. XRD, EDX and HRTEM indicated that the nanowires were wurtzite GaN single crystals. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 9 August 2000     

Preparation and photocatalytic activity of Mo-doped WO3 nanowires

Mo-doped WO₃ nanowires were fabricated by a hydrothermal method in the presence of K₂SO₄. The physical properties of prepared nanowires were characterized by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the obtained products are nanowires with diameters ranging between 10 and 20 nm, and lengths of about 600 nm. Its photoactivity was evaluated through the photodegradation of methylene blue (MB) in aqueous solution. Effects of the molybdenum concentration on the photoactivity of the obtained samples were investigated detailedly. The experimental results indicated that the Mo-doping enhanced the photoactivity of WO₃ nanowires.     

Self-assembly of Sb2O3 nanowires into microspheres: Synthesis and characterization

Sb₂O₃ nanowires with diameters of ∼233 nm and microspheres assembled by these nanowires were successfully synthesized by a simple poly-(vinylpyrrolidone) (PVP) assisted hydrothermal method. The morphologies, nano/microstructures and optical properties of the as-grown nanowires and microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflection spectrum. It has been found that the experimental parameters, such as mineralizers, played crucial roles in the morphological control of Sb₂O₃ nanowires. The possible growth mechanism of microspheres has been proposed.     

Thioglycolic acid (TGA) assisted hydrothermal synthesis of SnS nanorods and nanosheets

Nanorods and nanosheets of tin sulfide (SnS) were synthesized by a novel thioglycolic acid (TGA) assisted hydrothermal process. The as prepared nanostructures were characterized by X-ray diffraction (XRD) study, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD study reveals the formation of well-crystallized orthorhombic structure of SnS. Diameter of the SnS nanorods varied within 30-100 nm. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns identify the single crystalline nature for the SnS nanocrystals. The mechanism for the TGA assisted growth for the nanosheets and nanorods have been discussed.     

Facile hydrothermal synthesis of ultrahigh-aspect-ratio V2O5 nanowires for high-performance supercapacitors

Ultrahigh-aspect-ratio V₂O₅ nanowires were successfully prepared using [VO(O₂)₂(OH₂)]⁻ as the starting material by a template-free hydrothermal route without the addition of organic surfactant or inorganic ions. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The results revealed that the peroxovanadium (V) complexes can be easily transformed to V₂O₅ nanowires by this hydrothermal route. The uniform nanowires were with width about 50 nm and length about dozens of micron. The BET analysis showed the V₂O₅ nanowires had a high specific surface area of 25.6 m² g⁻¹. The synthesized V₂O₅ nanowires performed a high capacitance of 351 F g⁻¹ when used as supercapacitor electrode in 1 mol L⁻¹ LiNO₃.