Preparation and characterization of SiC nanowires and nanoparticles from filter paper by sol–gel and carbothermal reduction processing

The carbothermal reduction of SiO₂ gel containing filter paper (as carbon precursors) in argon was used to prepare SiC nanowires and nanoparticles. The resulting SiC ceramic, as well as the conversion mechanism of carbon/silica composites to SiC nanowires and nanoparticles, have been investigated by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TG) techniques. XRD and IR studies show that the materials, obtained from reaction at 1550 °C for 1 h in static argon atmosphere, are β-SiC. SEM and TEM reveal that SiC nanowires is single crystal wires with diameters ranging from 50–200 nm and their lengths over several tens of microns. According to thermodynamic analysis, SiC nanowires and SiC nanoparticles in the resulting SiC ceramic are formed by gas-gas reaction of SiO (g) and CO (g).     

Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

Synthesis of the tube-brush-shaped SiC nanowire array on carbon fiber and its photoluminescence properties

Tube-brush-shaped nanostructure of SiC nanowires was synthesized on polyacrylonitrile-based carbon fibers. The morphology and microstructure of the nanowires were characterized by X-ray powder diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. A quasi-periodically twin structure with (111) plane as the boundary along the SiC nanowires was observed. The vapor-solid growth mechanism of the SiC nanowire brush is also discussed. Moreover, some separated blue-shifted photoluminescence peaks around 469 nm were measured. The separated blue-shifted emission peaks are attributed to the quantum confinement of nanoscaled twin segments along each nanowire rather than the apparent diameters of the nanowires. The SiC nanowire brushes hopefully can find potential applications in nanotechnology.     

Tuning the morphologies of SiC nanowires via the control of growth temperature, and their photoluminescence properties

Single crystalline SiC nanowires were synthesized by a catalyst free vapor deposition method using elemental silicon and graphite carbon as the starting materials. The phase, morphology, crystal structure, and defects of the products were characterized by x-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Within a 6?h reaction time, the morphology of the SiC nanowires can be tuned to cylinder, hexagonal prism, or bamboo shape by simply altering the reaction temperature from 1470?°C, 1550?°C to 1630?°C, respectively. The photoluminescence of these differently shaped SiC nanowires was measured and is discussed. Based on the characterization results, the vapor-solid growth mechanisms for the multi-shaped SiC nanowires are proposed by taking into account the possible reactions between intermediate gas phases, the reaction steps, and the surface energy minimization.     

Field emission performance of SiC nanowires directly grown on graphite substrate

Lawn-like SiC nanowire arrays were successfully synthesized on graphite substrates by thermal evaporation of silicon powders at high temperature. The morphology, microstructure and composition of the nanowires were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The product grown on graphite substrates was hexagonal prism-shaped single-crystal 3C-SiC nanowires with high aspect ratio. Planar defects, such as microtwins and stacking faults were observed in SiC nanowires. Field emission measurements of the SiC nanowires grown on graphite substrate showed a very low threshold field of 2.1 V μm⁻¹, high brightness and stable field emission performance.     

Synthesis of ZnO nanowires by the hydrothermal method,using sol–gel prepared ZnO seed films

Zinc oxide (ZnO) nanowires with various morphologies are synthesized by the hydrothermal method on silicon substrates coated with ZnO thin films. The ZnO films are used as the seed layer and are prepared using the sol–gel technique. Experimental results demonstrate that the synthesis of ZnO nanowires is dependent on the crystalline properties of the ZnO seed-layer films. Sol concentration is the controlled parameter for the preparation of ZnO seed-layer films in this study. The ZnO films are found to have the hexagonal wurtzite structure with highly preferred growth along the c-axis at suitable sol concentrations. The vertically aligned ZnO nanowire arrays on the substrates are believed to be the result of the epitaxial growth of the ZnO seed layer. Scanning electron microscopy shows that nanowires with uniform distribution in length, diameter, and density are obtained. X-ray diffraction patterns clearly reveal that the ZnO nanowires are primarily grown along the c-axis direction. Transmission electron microscopy and selected-area electron diffraction measurements show that the nanowires have good crystalline properties. The well-aligned and high surface areas of the ZnO nanowires make them a potential candidate for applications in solar cells, field emission devices, and ultra-sensitive gas sensors.     

A novel method for massive fabrication of β-SiC nanowires

Silicon carbide nanowires (NWs), that were over 200 μm in length and 20–200 nm in diameter, were prepared by high-pressure reaction from SiBONC powder tablets. Annealing temperatures between 1,500 °C and 1,600 °C and Si/B molar ratios between 70:30 and 60:40 were suitable for the growth of the nanowires. The nanowires were fabricated by in situ chemical vapor growth process on the tablets. The SiC nanowires were identified as single crystal β-SiC. The analysis of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed the single crystalline nature of nanowires with a growth direction of <111>. Massive growth of single crystalline SiC nanowires is important to meet the requirements of the fabrication of SiC nanowire-based nanodevices.     

Fabrication and optical properties of mesoporous SnO2 nanowire arrays

Large-scale SnO2 mesoporous nanowires have been successfully synthesized by an improved sol-gel method within the nanochannels of porous anodic alumina templates. In this method, chloride of stannic and urea are used as precursors, chloride of stannic is acting as source of tin ions, and urea offers a basic medium through its hydrolysis. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction are used to characterize the SnO2 mesoporous nanowires. It is found that the as-prepared nanowires consist of SnO2 nanoparticles and pores. They can be indexed as rutile structures and diameters are about 50-70 nm. The growth mechanism of the mesoporous nanowires is also been discussed. The band gap of the as-prepared mesoporous nanowires is 3.735 eV, determined by UV/visible absorption spectral results. The SnO2 mesoporous nanowires show strong and stable photoluminescence with emission peak centered at 3.730 eV, which has never been reported in nanowires. It could be attributed to the exciton recombination.     

Scalable fabrication of novel SiC nanowire nonwoven fabric

Flexible papers constructed by one-dimensional nanowires have attracted much attention due to their various applications. Herein, a novel nonwoven fabric with paper-like qualities composed of zinc blende SiC (β-SiC) nanowires was fabricated by a scalable rolling process. The SiC nanowires were synthesized by the carbothermal reduction reaction of the carbon fiber and carbonaceous silica xerogel. The crystal phase, morphology and microscopic structure of the as-prepared SiC nanowires were characterized by field emission scanning electron microscope, X-ray diffraction and high-resolution transmission electron microscopy. The nanowire vapor–solid growth mechanism and preparation process for SiC nanowire nonwoven fabric were also discussed. The freestanding SiC nanowire nonwoven fabric exhibited high flexibility, high mechanical strength, excellent refractory performance and thermal stability. With high flexibility, high mechanical strength, superior nonflammability and thermal stability, the flexible paper-like 3C-SiC nanowire nonwoven fabric materials would be expected to have some potential applications, such as ceramic matrix composites, metal matrix composites, energy storage, catalyst supports, radiation-proof fabric, filtration and separation.     

Direct growth of core-shell SiC-SiO(2) nanowires and field emission characteristics

A simple, direct synthesis method was used to grow core-shell SiC-SiO(2) nanowires by heating NiO-catalysed silicon substrates. A carbothermal reduction of WO(3) provided a reductive environment and carbon source to synthesize crystalline SiC nanowires covered with SiO(2) sheaths at the growth temperature of 1000-1100?°C. Transmission electron microscopy showed that the SiC core was 15-25?nm in diameter and the SiO(2) shell layer was an average of 20?nm in thickness. The thickness of the SiO(2) shell layer could be controlled using hydrofluoric acid (HF) etching. Field emission results of core-shell SiC-SiO(2) and bare SiC nanowires showed that the SiC nanowires coated with an optimum SiO(2) thickness (10?nm) have a higher field emission current than the bare SiC nanowires.     

Large-scale synthesis and characterization of hexagonal prism-shaped SiC nanowires

Abundant hexagonal prism-shaped SiC nanowires were synthesized on graphite substrate via heating silicon in a graphite crucible. The products were characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The characterization first showed that the product was nanowires of beta-SiC with almost a perfect hexagonal cross section. The growth was determined along [111] direction. The six side surfaces look smooth under low magnification microscopy, but faceted at high magnification. Based on the characterization results, a formation mechanism combining vapor-solid (VS) growth mechanism and the lowest surface energy principle is proposed.     

Cu2S nanostructures prepared by Cu-cysteine precursor templated route

A facile Cu-cysteine precursor templated route for the synthesis of Cu₂S nanowires, dendritic-like and flowerlike nanostructures is reported. The Cu-cysteine precursors are prepared through the reaction between Cu²⁺, l-cysteine and ethanolamine at room temperature, and the morphologies of Cu-cysteine precursors can be controlled by adjusting the molar ratio of l-cysteine to Cu²⁺. The Cu-cysteine precursors are used as both templates and source materials for the subsequent preparation of polycrystalline Cu₂S nanostructures by thermal treatment, and the morphologies of the precursors can be well preserved after the thermal transformation to Cu₂S nanostructures. The samples are characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy.     

A simple route to ultra long SiC nanowires

SiC nanowires are prepared by pyrolysis of hexamethyldisilane (HMDS), at 1200 degrees C in a flowing Ar atmosphere. The length of the nanowires is in millimeter scale. Transmission electron microscopy observations indicate that the diameters of the SiC nanowires are in the range of about 8 to 120 nm, and that most of the nanowires have numerous stacking faults. The formation mechanism of the nanowires is proposed.     

Synthesis of SiC nanowires with in-situ deposition of carbon coating

SiC nanowires are effective reinforcement materials in ceramic matrix composites. A compliant coating such as carbon on nanowires is necessary in order to moderate the nanowire/matrix interfacial bounding for taking the most advantages of SiC nanowires. SiC nanowires with an in-situ deposition of carbon shell coating were fabricated by a novel chemical vapor growth process. Highresolution transmission electron microscopy examinations showed that the nanowires consisted of a single crystal beta-SiC core with an amorphous carbon shell 2-5 nm in thickness. The nanowires were straight with a length generally over 10 microm and a diameter 15-150 nm. The growth direction of the core SiC nanowires is (111). A simple three-step growth model for SiC nanowires was proposed based on a vapor-solid growth mechanism. Because the carbon-coated nanowires were grown directly on continuous Tyranno-SA SiC fibers, in-situ application of the present technique on the fabrication of SiC nanowire-reinforced SiC/SiC composites is expected.     

Synthesis of nanostructured SiC using the pulsed laser deposition technique

We report the new results on the direct synthesis of nanostructured silicon carbide (SiC) materials using the pulsed laser deposition technique. Scanning electron microscopy images revealed that SiC nanoholes, nanosprouts, nanowires, and nanoneedles were obtained. The crystallographic structure, chemical composition, and bond structure of the nanoscale SiC materials were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. The transverse optical mode and longitudinal optical mode in Raman spectra were found to become sharper as the substrate temperature was increased, while the material structure evolved from amorphous to crystalline.     

Synthesis and investigation of silicon carbide nanowires by HFCVD method

Silicon carbide (SiC) nanowire has been fabricated by hot filament chemical vapour deposition (HFCVD) mechanism in the temperature range of 600–800°C. Synthesis is performed under vacuum in the atmospheres of hexamethyldisiloxane/alcohol (HMDSO/C₂H₅OH) vapour and hydrogen (H₂) gas mixture. In this research dependence of SiC properties on temperature is discussed. Morphology and structural properties of SiC nanowire grown on glass substrate were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy diffraction spectrometer (EDX), and four-point probe (4PP). Also Mountains Map Premium (64-bit version) software is used to investigate morphological features of samples. In this context, the analysis of the motifs, depth histograms, statistical parameters, texture direction, fractal, and the peak count histograms of the nanostructure surface of samples are carried out. According to analysis, SiC films had a good crystal quality without defects or low residual stress. We found that increasing substrate temperature increases silicon and oxygen doping amount. We also found that electrical resistivity and surface roughness increased by increasing substrate temperature. This study showed that SiC nanowires with high density grew on the free catalyst glass substrate, and the alignment of SiC nanowires decreased.     

核壳结构SiC/SiO2纳米线的低温合成与表征

以酚醛树脂(PF)作为碳源, 纳米SiO₂为硅源, 在1300℃氩气气氛下通过碳热还原反应, 制备出具有核壳结构的SiC/SiO₂纳米线。采用X射线分析衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨率透射电子显微镜(HRTEM)、拉曼光谱(Raman)对产物的组成、形貌、微观结构等进行了表征。结果表明; SiC/SiO₂纳米线长可达数毫米, 单根SiC/SiO₂纳米线由直径30 nm的β-SiC晶体为内核和厚度约12 nm的无定形SiO₂壳层组成; 室温下SiC/SiO₂纳米线的PL发光峰与β-SiC单晶的发光特征峰相比有蓝移。最后, 讨论了核壳结构SiC/SiO₂纳米线的生成机制。     

Molten salt route of single crystal barium titanate nanowires

Rather long barium titanate nanowires have been synthesised by molten salt method without any organic surfactants. The crystal structure of barium titanate nanowires is identified by X-ray diffraction to be the tetragonal structure phase, Raman spectroscopy and selected area electron diffraction measurements. Furthermore, scanning electron microscopy and transmission electron microscopy observations show that the barium titanate nanowires have uniform cylindrical structure, with lengths from 20 to 80 μm and diameters from 100 nm to 1 μm. Moreover, high resolution transmission electron microscopy observations and selected area electron diffraction analysis show that the barium titanate nanowires are single crystals with a tetragonal structure in nature.     

Preparation and microwave absorbing properties of SiC microtubes

Using cotton as carbon source and template, SiC microtubes were prepared by the carbothermal reduction of a cotton-contained precursor, which was obtained by impregnating cotton in tetraethyl orthosilicate solution. To characterize the product, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and network analyzer were used. The results show that the SiC microtubes with surfaces composed of villus-like β-SiC nanowires have a length of tens to hundreds of micrometers and a diameter of several to 20 μm. SiC microtubes achieve a reflection loss below −10 dB (90% absorption) at different frequencies, and the minimum value is −23.9 dB at 17.5 GHz when its thickness is 1 mm.     

Hydrothermal synthesis of layered sodium manganese oxide nanowires and their electrochemical performance

A new method for preparing black birnessite nanowires is introduced. Layer-structured manganese oxide nanowires were synthesized by a facile hydrothermal method, and using both NaMnO4 and CH3CH2OH as the precursors in a concentrated NaOH solution. The structure, composition, appearance and electrochemical performance of the product were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy diffraction (ED), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA) and constant current charge/discharge. The XRD patterns showed a single phase corresponding to a crystalline birnessite-based manganese oxide. TEM studies suggested their wire-like structures. The TGA measurement demonstrated that they possessed an excellent thermal stability up to 400 degrees C. In the potential window of 2.0-4.3 V, the product exhibited excellent cyclic stability and rapid charge-discharge performance.