Hydrothermal synthesis of mesoporous VO2·½(H2O) nanosheets and study of their electrical properties

Layered sheet-like nanocrystalline VO₂·½(H₂O) has been synthesized by hydrothermal process using V₂O₅ as vanadium source and 2-phenylethylamine as a reducing agent and a structure-directing template. Techniques X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption/desorption isotherms have been used to characterize the structure, morphology and composition of the materials. Electrical conductivity measurements showed that the as synthesized VO₂·½(H₂O) nanosheets has a conductivity value which goes from 75 × 10^?6 Ω^?1 cm^?1 at 298 K, to 68 10^?5 Ω^?1 cm^?1 at 386 K with activation energy of 0.24 eV.     

Preparation,crystal structure and characterization of α-NaSbP2S6 and β-NaSbP2S6 phases

The new phases α-NaSbP₂S₆ and β-NaSbP₂S₆ were synthesized by ceramic and reactive flux methods at 773 K. The structures of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by the single-crystal X-ray diffraction technique. α-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁/c with a = 11.231(2) Å, b = 7.2807(15) Å, c = 11.640(2) Å, β = 108.99(3)°, V = 900.0(3) Å³ and z = 4. β-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁ with a = 6.6167(13) Å, b = 7.3993(15) Å, c = 9.895(2) Å, β = 92.12(3) °, V = 484.10(17) Å³ and z = 2.The α- and β-phases of NaSbP₂S₆ are closely related, the main difference lies in the stacking of the [Sb[P₂S₆]]_nⁿ⁻ layers. The structure of α-NaSbP₂S₆ consists of two condensed layers (MPS₃ type) to give an ABAB… sequence with Na⁺ cations located in the interlayer space. The packing of β-NaSbP₂S₆ is formed by monolayers of [Sb[P₂S₆]]_nⁿ⁻ stacked in an AA… fashion separated by a layer of Na⁺ cations. Both phases are derivates of the M¹⁺M³⁺P₂Q₆ family.The optical band gaps of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by UV–vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively.     

Synthesis and electrochemical properties of Ag0.333V2O5–V2O5 core–shell nanobelts for rechargeable lithium batteries

Ag_0.333V₂O₅–V₂O₅ core–shell nanobelts have been synthesized by a facile homogeneous reaction between peroxovanadic acid and AgNO₃ under hydrothermal conditions. The formation of Ag_0.333V₂O₅–V₂O₅ core–shell nanobelts is time dependent: Ag_0.333V₂O₅ nanobelts are formed firstly, and then V₂O₅ grows on the Ag_0.333V₂O₅ surfaces. The core–shell nanobelts exhibit stable lithium-ion intercalation/deintercalation reversibility and deliver specific discharge capacities of around 276.4 mAhg^?1 after 50 cycles at a rate of 0.25 Ag^?1. The value is lowered to 228 mAhg^?1 at 0.5 Ag^?1, and 147.2 mAhg^?1 at 0.75 Ag^?1. The good electrochemical properties of Ag_0.333V₂O₅–V₂O₅ core–shell nanobelts make them a promising candidate as a cathode material for rechargeable lithium batteries.     

Enhancement of the coercivity of electrodeposited nickel nanowire arrays

In the present study, the single-crystal Ni nanowire arrays with a preferred growth along the [110] direction have been prepared by the deposition of Ni into the alumina template with nanopores at a current density of 2.0 mA/cm². The single-crystal Ni nanowire arrays show a magnetic anisotropy with the easy axis parallel to the nanowires and an enhanced coercivity as compared with the polycrystalline Ni nanowire arrays. A large coercivity of 1110 Oe together with a high remanence M_r = 0.92M_s is observed for 15-nm diameter single-crystal Ni nanowire arrays. The preferred growth mechanism of the single-crystal nanowires is briefly discussed.     

Amorphous InGaZnO thin film transistors with SiO2/HfO2 double-layer gate dielectric fabricated at low temperature

Amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with double-layer gate dielectric were fabricated at low temperature and characterized. A stacked 150 nm-thick SiO₂/50 nm-thick HfO₂ dielectric layer was employed to improve the capacitance and leakage characteristics of the gate oxide. The SiO₂/HfO₂ showed a higher capacitance of 35 nF/cm² and a lower leakage current density of 4.6 nA/cm² than 200 nm-thick SiO₂. The obtained saturation mobility (μ_sat), threshold voltage (V_th), and subthreshold swing (S) of the fabricated TFTs were 18.8 cm² V^?1 s^?1, 0.88 V, and 0.48 V/decade, respectively. Furthermore, it was found that oxygen pressure during the IGZO channel layer deposition had a great influence on the performance of the TFTs.     

Structure and field emission properties of SnO2 nanowires

SnO₂ nanowires were fabricated using a simple and economical method of rapid heating SnO₂ and graphite powders at 850 °C in a flow of high-purity N₂ as carrier gas. Research by using X-ray diffraction (XRD) indicates that SnO₂ nanowires are primitive tetragonal in structure with the lattice constant a = b = 0.443 nm and c = 0.372 nm. Observations by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that SnO₂ is of nanowire structure. The selected area electron diffraction (SAED) shows that the nanowires are perfect single crystal structure. The Fourier transform infrared (FT-IR) exhibits the difference of nanostructure materials and general materials. The field emission (FE) properties had also been studied.     

Polyaniline nanowire electrodes with high capacitance synthesized by a simple approach

Polyaniline (PANI) nanowire electrodes were successfully synthesized by electrodeposition using starch as template. The electrodes were characterized with scanning electron microscope (SEM) and X-ray diffraction technique. SEM images showed that the electrodes electrodeposited using the starch template had nanowire morphology, but the PANI electrodeposited in absent solution had agglomerate block morphology. Cyclic voltammograms at different scan rates and charge–discharge tests were performed in 0.5 M H₂SO₄ aqueous solution. The PANI nanowire electrodes had a high capacitance (882 F g^? 1) and a high stability (5% capacity loss after 500 cycles).     

Development of a conductive composite based on polythiophene/Y-zeolite and its response towards sulfide ions

A new potentiometric sensor electrode for sulfide based on conducting polymer films is introduced. A composite of polythiophene (PTP) with Y-zeolite was prepared via chemical oxidative polymerization of thiophene (TP) in presence of a dispersion of Y-zeolite (powder) in CHCl3 solvent using anhydrous FeCl3 oxidant. Formation of polythiophene and its subsequent SEM and TEM analysis revealed formation of composite particles with average diameter in the range of 0.3–0.35 μm. DC conductivity value of the PTP-Y-zeolite composite was in the order of 10? 2 S/cm, which was indeed high compared to that of PTP, produced under identical conditions as above without the presence of Y-zeolite. This composite as active component with graphite powder and binding liquid was mixed and then used for preparation of solid state electrodes. The working temperature range for this electrode is between 20 and 40 °C. The linear dynamic range is 1 × 10? 7 – 1 × 10? 4 M and measures total sulfide concentration over a range of pH from 5 to 9. The composite electrode showed high selectivity for sulfide in the presence of many common interfering anions (? log KS, IO3?Pot = 6.3, ? log KS, BrO3?Pot = 5.5, ? log KS, S2O32 ?Pot = 4.8).     

Synthesis of bundled tungsten oxide nanowires with controllable morphology

Bundled tungsten oxide nanowires with controllable morphology were synthesized by a simple solvothermal method with tungsten hexachloride (WCl₆) as precursor and cyclohexanol as solvent. The as-synthesized products were systematically characterized by using scanning electron microscopy, X-ray diffraction and transition electron microscopy. Brunauer–Emmett–Teller gas-sorption measurements were also employed. Accompanied by an apparent drop of specific surface area from 151 m² g^? 1 for the longer nanowires synthesized using a lower concentration of WCl₆ to 106 m² g^? 1 for the shorter nanowires synthesized using a higher concentration of WCl₆, a dramatically morphological evolution was also observed. With increasing concentration of tungsten hexachloride (WCl₆) in cyclohexanol, the nanostructured bundles became larger, shorter and straighter, and finally a block-shape product occurred.     

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.     

Growth of CuInTe2 single crystals by iodine transport and their characterization

The single crystals with stoichiometry close to 1:1:2 of CuInTe₂ (CIT) have been grown by chemical vapor transport (CVT) technique using iodine as the transporting agent at different growth temperatures. Single crystal X-ray diffraction studies have confirmed the chalcopyrite structure for the grown crystals and the volume of unit cell is found to be the same for the crystals grown at different conditions. Energy dispersive X-ray (EDAX) analysis of CIT single crystals grown shows almost the same stoichiometric compositions. Scanning electron microscope (SEM) analysis reveals kink, step and layer patterns on the surface of CIT single crystals depending on the growth temperatures. The optical absorption spectra of as-grown CIT single crystals grown at different conditions show that they have same band gap energies (1.0405 eV). Raman spectra exhibit a high intensity peak of A₁ mode at 123 cm^?1. Annealed at 473 K in nitrogen atmosphere for 40 h CIT single crystals have higher hole mobility (105.6 cm²V^?1s^?1₎ and hole concentration (23.28 × 10¹⁷ cm^?3) compared with values of hole mobility (63.69 cm² V^?1 s^?1) and hole concentration (6.99 × 10¹⁵ cm^?3) of the as-grown CIT single crystals.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Growth of SiO2 hierarchical nanostructure on SiC nanowires using thermal decomposition of ethanol and titanium tetrachloride and its FTIR and PL property

Novel SiO₂ hierarchical nanostructure has been grown on SiC nanowires using thermal decomposition of a mixture of ethanol and titanium tetrachloride. Novel nanostructure was realized in one synthesis route. Based on SEM and TEM observations, the hierarchical nanostructure consists of core-shell SiC–SiO₂ main stem nanowire and a lot of SiO₂ nanorod branches grown on the main stem. A mean diameter of SiC central cores was about 40 nm and their lengths reach about 100 μm. The lengths and diameters of SiO₂ nanorod-like branches were ranged in 400–800 nm and 30–120 nm, respectively. The growth of core-shell SiC–SiO₂ nanowires obeyed vapor–liquid–solid mechanism and the SiO₂ nanorod-like branches grew via vapor–solid mechanism. The infrared absorption and photoluminescence properties of the grown nanostructure were investigated.     

Effect of chitosan content on gel content of epoxized natural rubber grafted with chitosan in latex form

The epoxidized natural rubber (ENR) latex-g-chitosan (ENR-g-chitosan) was prepared in latex form using potassium persulphate as an initiator. Firstly, the reduction in molecular weight of chitosan was subjected to the addition of K₂S₂O₈ at 70 °C for 15 min. The structure of the modified chitosan was characterized by ATR-FTIR. Secondarily, the influence of chitosan contents, reaction time, and temperature and K₂S₂O₈ concentrations on the gel content of the modified ENR was investigated. The chemical structure of the ENR-g-chitosan was confirmed by ¹H-NMR and ATR-FTIR. The ether linkage of the ENR-g-chitosan was conformed at 1154 an 1089 cm^? 1 by ATR-FTIR and 3.60 ppm by ¹H-NMR. The gel content of ENR-g-chitosan at 5% chitosan showed the highest value compared with other samples. But when chitosan increased from 5% to 10% or 20%, the gel content of ENR-g-chitosan dramatically decreased. The ENR-g-chitosan showed good thermal resistance due to incorporation of chitosan. The morphology of ENR-g-chitosan particle showed the core-shell structure observed by TEM. The optimum condition of grafting ENR with chitosan was found at 65 °C for 3 h of reaction time, ratio of ENR/chitosan at 9:1.     

Synthesis and characterization of flower-like CuIn1−xGaxS2 (x = 0.3) microspheres

We report the formation and characterization of the flower-like CuIn_1?xGa_xS₂ (x = 0.3) microspheres using CuCl₂·2H₂O, GaCl₃, InCl₃ and l-cystine in the mixed solvent of ethylene glycol and distilled water (1:2, v/v) at 200 °C for 24 h. XRD results indicated that the CuIn_0.7Ga_0.3S₂ nanostructures have a (1 1 2) preferred orientation. The EDS and XPS analyses of the sample revealed that Cu, In, Ga and S were present in an atomic ratio of approximately 1:0.7:0.3:2. FESEM and TEM images showed that the product was microspheres, consisting of nanoplates with the thickness of about 20 nm. The optical properties were investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and Raman spectroscopy. UV–vis absorption spectrum indicated that the band gap of as-synthesized flower-like CuIn_0.7Ga_0.3S₂ microspheres was about 2.427 eV. Raman spectrum of the obtained CuIn_0.7Ga_0.3S₂ exhibited a high-intensity peak at 302 cm^?1 could be assigned as A1-mode.     

Electroanalytical properties and application of anthraquinone derivative-functionalized multiwalled carbon nanotubes nanowires modified glassy carbon electrode in the determination of dissolved oxygen

We herein report a simple, low cost and green preparation of nanowires of (anthraquinone-2-carboxylic acid/amino functionalized) multiwalled carbon nanotubes (HOOC-2-AQ/AMWCNTs) which has been further employed for the development of highly sensitive oxygen sensor. The prepared composite has been characterized by TEM and electrochemical studies. The glassy carbon electrode modified with composite shows an irreversible and good electrocatalytic activity for the reduction of oxygen. The reduction potential of the oxygen was shifted 460 mV towards the positive potential with this modified electrode as compared to bare glassy carbon electrode. The prepared material was stable with no leaching observed of the mediator. A linear response range of 0.2–6.8 mg L^?1, with a sensitivity of 5.0 μA L mg^?1 and a detection limit of 0.02 mg L^?1 were obtained with this sensor.     

Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10¹⁴ m^?2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10¹⁴ m^?2, lattice thermal conductivity would be independent of that.     

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.     

TiO2 nanotube-based field effect transistors and their application as humidity sensors

TiO₂ nanotubes are the building units of various devices of energy- and environment-related applications and the property studies of individual TiO₂ nanotubes are important to understand and improve the performance of TiO₂ nanotubes-based devices. Here we report the electrical property study of individual TiO₂ nanotubes enabled by the construction of field effect transistors based on individual TiO₂ nanotubes. It is found that individual TiO₂ nanotubes exhibit typical n-type electrical conduction characteristics, with electron mobility of 6.9 × 10^?3 cm²/V s at V_ds = 1 V, and electron concentration of 2.8 × 10¹⁷ cm^?3. Moreover, the on–off ratio of the TiO₂ nanotube-based field effect transistors is as high as 10³. Humidity sensing test shows the sensitive response of the individual TiO₂ nanotubes to water vapor.     

Hydrothermal synthesis,characterization and electrical investigation of poly(para-phenylenediamine)/vanadium oxide nanocomposite nanosheets

Sheet-like mesoporous poly(paraphenylenediamine)/vanadium oxide nanocomposite has been synthesized by the hydrothermal process using the vanadium oxide V₂O₅ as inorganic precursor and paraphenylendiamine as reducing and a structure-directing agent. Such techniques as X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption isotherms (BET) have been used to characterize the structure, morphology and the texture of the material. The conductivity of the material was measured by complex impedance spectroscopy which increases from 72 × 10^?5 Ω^?1 cm^?1 at 298 K to 95 × 10^?4 Ω^?1 cm^?1 at 493 K. The Arrhenius diagram is not linear, it presents a rupture situated at 407 K and the activation energies’ average values are 0.044 eV and 0.13 eV.