Synthesis of magnesium borate (Mg2B2O5) nanowires,growth mechanism and their lubricating properties

Large quantities of single crystalline magnesium borate nanowires of the form Mg₂B₂O₅ with typical diameter about 120–180 nm and length about 0.2 mm have been successfully synthesized by a new and simple method of heating the mixed tablet of Mg(BO₂)₂ and graphite directly in vacuum at 1200 °C for 1 h. The products have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and selected area electron diffraction. The process of the nucleation and the growth of nanowires have been analyzed by VS mechanism. The results of the lubricating properties show that the friction coefficient of the oil is significantly decreased by the addition of Mg₂B₂O₅ nanowires. Our results indicate that the new method we use is effective in synthesis of Mg₂B₂O₅ nanowires and the nanowires can be used as additive to antiwear nanodevices.     

Fabrication of needle-shaped GaN nanowires by ammoniating Ga2O3 films on MgO layers deposited on Si (111) substrates

Needle-shaped GaN nanowires have been synthesized on Si (111) substrate through ammoniating Ga₂O₃/MgO films under flowing ammonia atmosphere at the temperature of 950 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that these nanowires are hexagonal GaN and possess a smooth surface with an average diameter about 200 nm and a length ranging from 5 μm to 15 μm. In addition, the diameters of these nanowires diminish gradually. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

A green and facile route to synthesize calcium silicate nanowires

Large-scale single crystalline calcium silicate nanowires have been synthesized via a simple and facile hydrothermal route using nanoscale SiO₂ and CaO powders as the starting materials. Xonotlite [Ca₆(Si₆O₁₇)(OH)₂] nanowires were first achieved after hydrothermal treatment at 220 °C for 12 h. After being calcinated at 800 °C for 1 h, the Ca₆(Si₆O₁₇)(OH)₂ nanowires are completely transformed into β-CaSiO₃ nanowires. The β-CaSiO₃ nanowires have a diameter of 30–150 nm and a length of tens of micrometers. The hydrothermal conditions and the size of the raw materials play important roles on the size of the nanowires. A possible growth mechanism of the nanowires is also proposed.     

Preparation of α-MnO2 nanowires through a γ-MnOOH precursor route

In the absence of extra surfactant or template, single crystalline γ-MnOOH nanowires were prepared directly via a hydrothermal method using KMnO₄ and CO(NH₂)₂ as starting materials at 120 °C for 12 h; and single crystalline α-MnO₂ nanowires could be obtained after calcining the γ-MnOOH nanowire precursor in air at 320 °C for 5 h. Various measurements were used to characterize the structure, morphology and electrochemical behavior of the resultant products. The urea acted as an important reagent and its participation was believed to contribute to the formation and growth of γ-MnOOH nanowires and even benefit the improvement of the electrochemical properties of the prepared α-MnO₂ nanowires.     

Preparation and photoluminescence of high density SiOx nanowires with Fe3O4 nanoparticles catalyst

Large scale, high density SiOx nanowires have been synthesized using a novel Fe₃O₄ nanoparticles catalyst. The lengths of SiOx nanowires are in the range of several tens to hundreds of micrometers, and the diameters of nanowires are 20–80 nm. Transmission electron microscopy and high-resolution transmission electron microscopy show that the SiOx nanowires are amorphous, and energy dispersive X-ray spectrometry analysis reveals that SiOx nanowires consist of Si and O elements in an atomic ratio of approximately x = 1.4–1.7. The vapor–liquid–solid (VLS) mechanism is the main formation mechanism of SiOx nanowires. The SiOx nanowires have two broad photoluminescence peaks at about 405 nm and 465 nm when the 250 nm ultraviolet fluorescent light excitation is applied at room temperature. The SiOx nanowires with good photoluminescence properties are promising candidates for ultraviolet–blue optical emitting devices.     

Synthesis and characterization of copper telluride nanowires via template-assisted dc electrodeposition route

Using polycarbonate track-etch membranes (Whatman), copper telluride (Cu_1.75Te) nanowires of diameter 100 nm and 50 nm have been synthesized electrochemically via template-assisted electrodeposition technique on indium tin oxide (ITO) coated glass from aqueous acidic solution of copper (II) sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) at room temperature (30 °C). Scanning electron microscopy (SEM) reveals the morphology of the nanowires having uniform diameter equal to the diameter of the template used. X-ray diffraction (XRD) pattern showed the structure corresponding to the hexagonal structure of copper telluride and single-crystalline. Using UV–visible spectrometry, the optical band gap of copper telluride nanowires was found to be 3.092 eV for 100 nm and 3.230 eV for 50 nm diameters. The photoluminescence (PL) studies shows higher intensity and broad spectrum in the blue region (450–475 nm) of visible light spectrum.     

Enhancement of thermal stability of TiO2 nanowires embedded in anodic aluminum oxide template

Titania (TiO₂) nanowires with diameters of 20, 50, and 80 nm were successfully synthesized via the template-assistant method. The TiO₂ nanowires embedded in anodic aluminum oxide template have extremely high crystallization and anatase-to-rutile phase transition temperatures than that of the free-state TiO₂ powders, and the thermal stability of embedded TiO₂ nanowires depends on the diameter of the templates. The growth and nucleation activation energy of rutile in 20 nm nanowires are determined to be _boxclose E_{\rm{g}}  = 2.8 ± 0.2 eV and E_n E_{\rm{n}}  = 2.7 ± 0.2 eV, respectively, much higher than that of the free-state TiO₂ powders with E_g E_{\rm{g}}  = 1.6 ± 0.2 eV and E_n E_{\rm{n}}  = 1.9 ± 0.2 eV. The pressure induced by the difference of thermal expansion coefficient between the TiO₂ and aluminum oxide acts as an effective barrier that prevents phase transition, resulting in the enhancement of the TiO₂ structural stability.     

Large-scale SnO2 nanowires synthesized by direct sublimation method and their enhanced dielectric responses

In this paper, we developed a direct sublimation method to synthesize large-scale rutile SnO₂ nanowires on 6H–SiC substrate using SnO₂ nanoparticles as starting material. The structural properties of these straight nanowires were investigated in detail. These nanowires grow along [121], and the average diameter and length of these nanowires are 80 nm and 5 μm, respectively. In addition, the dielectric measurement indicates that the dielectric response of the SnO₂ nanowires is significantly enhanced in the low-frequency range. It is suggested that both the rotation direction polarization (RDP) and the space charge polarization (SCP) process should be responsible for the enhancement of ε_r of these SnO₂ nanowires.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Hydrothermal synthesis and magnetic properties of α-MnO2 nanowires

In the present study, one-dimensional (1D) α-MnO₂ nanowires with width of 50–60 nm, length about several micrometers have been successfully prepared under hydrothermal conditions in the presence of sodium carboxymethyl cellulose. The samples were characterized by X-ray diffraction, scanning electron microscope, superconducting quantum interference device and N₂ adsorption–desorption experiment. The magnetic measurement reveals that the α-MnO₂ nanowires exhibit a ferromagnetic behavior at 5 K and a paramagnetic behavior at 300 K. The N₂ adsorption–desorption experiment shows that surface area is 160.4 m² g^?1, which is even larger than those of mesoporous nanostructures. At the same time, the possible formation mechanism for the formation of α-MnO₂ nanowires has been proposed according to the experimental results.     

New composite films based on MoO<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript> nanowires aligned in a liquid single crystal elastomer matrix

Abstract  

In this study, we report the preparation, structure characterization, and application of new MoO_3−x nanowires, promising candidates for lithium intercalation, hydrogen sensing, and smart windows due to their photochromic property. These nanowires are a mixture of MoO₃ and conductive Mo₅O₁₄ phase and have been used to prepare composite films based on liquid single crystal elastomers (LSCE). The structure, morphology, and thermomechanic behavior of these films are discussed. In particular, we show that the particular combination of molybdenum-based nanowires and LSCEs allows for doping of liquid single crystal elastomers, preserving the pristine mechanical and optical properties of the host matrix.     

Synthesis of ZnGa2O4 nanowires with β-Ga2O3 templates and its photoluminescence performance

This paper focuses on a new but much simple approach in synthesizing cubic spinel-structure ZnGa₂O₄ nanowires through the reaction of β-Ga₂O₃ nanowires templates and ZnO vapor at high temperature. Characterization has been achieved by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The length of as-synthesized ZnGa₂O₄ nanowires is scaled over 10 μm and the diameter is 80 nm respectively. It has been noticed that the concentration of ZnO vapor plays an important role for synthesizing ZnGa₂O₄ nanowires. And with different concentration of ZnO vapor, the very nanowires could be compounded in the form of β-Ga₂O₃:ZnGa₂O₄, ZnGa₂O₄ and ZnO:ZnGa₂O₄. The corresponding photoluminescence emission bands centered at 460 nm, 405 nm and 381 nm have also been observed.     

Hydrothermal synthesis and indication of room temperature ferromagnetism in CeO2 nanowires

Bundle of CeO₂ nanowires have been successfully synthesized by a simple hydrothermal process using Ce(NO₃)₃·6H₂O as cerium source and NaH₂PO₄·2H₂O as mineralizer, into which no surfactant or template was introduced. The synthesized nanowires were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and magnetization measurements. The XRD results indicated that CeO₂ nanowires have fluorite structure. Magnetization measurements indicate that CeO₂ nanowires exhibit room temperature ferromagnetism with remanent magnetization (M_r) and coercivity (H_C) of about 7.44 × 10^? 4 (emu/g) and 27.19 Oe, respectively, which may results due to the presence of defects in the CeO₂ nanowires.     

Preparation and transformation to hollow nanospheres of wrapped CuS nanowires by a simple hydrothermal route

In this paper we reported the preparation of wrapped CuS nanowires via a simple hydrothermal reaction at 180 °C for 2 h, employing CuSO₄·5H₂O and thiourea as reactants in the absence of any structure-directing agent. SAED pattern showed that the wrapped CuS nanowires were polycrystalline, which was comprised of small nanoparticles. TEM observations showed that wrapped nanowires could grow and further transfer to hollow spheres with the prolonging of the reaction time from 2 h to 13. The UV-Vis spectra of CuS prepared at 180 °C for different times were studied. The possible transfer mechanism from wrapped nanowires to hollow spheres was suggested.     

Fabrication of Ag and Cu nanowires by a solid-state ionic method and investigation of their third-order nonlinear optical properties

Ag and Cu nanowires were separately fabricated in a direct current electric field using a solid-state ionic method, and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their optical nonlinearities induced by 8 ns laser pulses from a frequency-doubled, Nd:YAG laser at 532 nm, were investigated using the Z-scan technique. Experimental results indicate the metal nanowires have obvious positive refractive nonlinearities and reverse saturated absorption behaviors. The self-focusing behaviors of Ag and Cu nanowires can be attributed to Kerr-induced self-focusing of laser radiation, the nonlinear refractive indexes of Ag and Cu nanowires are n₂ = 1.7 × 10^− 11 esu and n₂ = 2.4 × 10^− 11 esu respectively, and the two-photon process of Ag and the one-photon process of Cu are responsible for the difference between Ag and Cu nanowires suspended in de-ionized water in nanosecond nonlinear absorptions.     

Composite Solid Electrolyte with Continuous and Fast Organic–Inorganic Ion Transport Highways Created by 3D Crimped Nanofibers@functional Ceramic Nanowires

A 3D crimped sulfonated polyethersulfone-polyethylene oxide(C-SPES/PEO) nanofiber membrane and long-range lanthanum cobaltate(LaCoO₃) nanowires are collectively doped into a PEO matrix to acquire a composite solid electrolyte (C-SPES-PEO-LaCoO₃) for all-solid-state lithium metal batteries(ASSLMBs). The 3D crimped structure enables the fiber membrane to have a large porosity of 90%. Therefore, under the premise of strongly guaranteeing the mechanical properties of C-SPES-PEO-LaCoO₃, the ceramic nanowires conveniently penetrated into the 3D crimped SPES nanofiber without being blocked, which can facilitate fast ionic conductivity by forming 3D continuous organic–inorganic ion transport pathways. The as-prepared electrolyte delivers an excellent ionic conductivity of 2.5 × 10⁻⁴ S cm⁻¹ at 30 °C. Density functional theory calculations indicate that the LaCoO₃ nanowires and 3D crimped C-SPES/PEO fibers contribute to Li⁺ movement. Particularly, the LiFePO₄/C-SPES-PEO-LaCoO₃ /Li and NMC811/C-SPES-PEO-LaCoO₃/Li pouch cell have a high initial discharge specific capacity of 156.8 mAh g⁻¹ and a maximum value of 176.7 mAh g⁻¹, respectively. In addition, the universality of the penetration of C-SPES/PEO nanofibers to functional ceramic nanowires is also reflected by the stable cycling performance of ASSLMBs based on the electrolytes, in which the LaCoO₃ nanowires are replaced with Gd-doped CeO₂ nanowires. The work will provide a novel approach to high performance solid-state electrolytes.     

Large-scale synthesis of single-crystal alpha manganese sesquioxide nanowires via solid-state reaction

Smooth single-crystal α-Mn₂O₃ nanowires have been fabricated using a one-step solid-state reaction method. X-ray diffraction patterns show that the nanowires have pure phase of α-Mn₂O₃. Transmission electron microscopy was employed to investigate the size and morphology of the products. The α-Mn₂O₃ nanowires exhibit mean diameter of 50 nm and length of 10 μm. Selected-area electron diffraction pattern demonstrates the single-crystal structure of the α-Mn₂O₃ nanowires, which are in good agreement with the X-ray diffraction results. The processes of the reactions and the phase transitions were also studied by using a simultaneous thermal gravimetric/differential thermal analyzer. It is found that the concentration of the precursor MnCO₃ is a crucial factor in the formation of the nanowires. This work provides the probability of the industrialization of fabricating smooth single-crystal α-Mn₂O₃ nanowires.     

Synthesis and characterization of C3N4 nanowires and pseudocubic C3N4 polycrystalline nanoparticles

C₃N₄ nanowires and pseudocubic C₃N₄ polycrystalline nanoparticles have been synthesized by the reaction between C₃N₃Cl₃ and NaN₃ with Zn powder as catalyst. The process was carried out using a constant-pressure benzene thermal method at 40 MPa and 220 °C. The prepared nanowires have a diameter range of 3-6 nm and length range of 100-200 nm, while the diameters of the nanoparticles range from 10 nm to 40 nm. The as-prepared samples were characterized by X-ray powder diffraction (XRD), Fourier transform spectroscopy (FTIR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).     

Silica-coated ZnO nanowires

ZnO-core/SiO_x shell nanowires were successfully fabricated and their morphology, structure, Raman and photoluminescence properties were examined. Not only the sputter-coated product had an one-dimensional morphology, but the tubular structure of SiO_x shell was also continuous, smooth, and uniform, along the core nanowires. It was found that two fundamental modes (334, 437 cm⁻¹) and 2 s order modes (1106, 1156 cm⁻¹) of hexagonal ZnO appeared in the Raman spectrum of ZnO-core/SiO_x shell nanowires. The photoluminescence (PL) spectrum of the core-shell nanowires were deconvoluted into three Gassian functions, centered at 382, 500, and 758 nm, whether the subsequent thermal annealing was performed or not. The integrated intensities of UV (382 nm) and green (758 nm) emissions were changed by means of the shell-coating and thermal annealing. We have discussed the possible emission mechanisms.