ZnO–SnO2 branch–stem nanowires based on a two-step process: Synthesis and sensing capability

ZnO–SnO₂ branch–stem nanostructures were realized on a basis of a two-step process. In step 1, SnO₂-stem nanowires were synthesized. In step 2, ZnO-branch nanowires were successfully grown on the SnO₂-stem nanowires through a simple evaporation technique. We have pre-deposited thin Au layers on the surface of SnO₂ nanowire stems and subsequently evaporated Zn powders on the nanowires. The ZnO branches, which sprouted from the SnO₂ stems, had diameters in a range of 30–35 nm. As-synthesized branches were of single crystalline hexagonal ZnO structures. Since the branch tips were comprised of Au-containing nanoparticles, the Au-catalyzed vapor–liquid–solid growth mechanism was more likely to control the growth process of the ZnO branches. To test a potential use of ZnO–SnO₂ branch–stem nanostructures in chemical gas sensors, their sensing performances with respect to NO₂ gas were investigated, showing the promising potential in chemical gas sensors.     

Effect of ZnF2 and WO3 on elastic properties of oxyfluoride tellurite ZnF2–WO3–TeO2glasses: Theoretical analysis

The elastic properties of oxyfluoride tellurite glasses in the ternary system ZnF₂-WO₃ -TeO₂ were analyzed and their changes when ZnF₂ was replaced with TeO₂ or WO₃ were predicted. The most significant structural and compositional parameters were evaluated on the basis of the well known models and approaches existing in the field and correlated with both elastic moduli and Poisson's ratio. It has been found that the molar volume, fractal bond connectivity, first-order stretching force constant of the Te–O and W–O covalent bonds and dissociation energy per unit volume of the constituent components play an important role in determining and predicting of elastic moduli. The semi-empirical formula of Abd El-Moneim and Alfifi, which correlates bulk modulus with the ratio between packing density and mean atomic volume, appears to be valid for the investigated oxyfluoride tellurite glasses. On the basis of Makishima-Mackenzie's theory, the agreement between the theoretically calculated and experimentally measured values is excellent for shear and Young's moduli and satisfactory for Poisson's ratio as well as bulk and longitudinal moduli. The slight divergence between the theoretical and experimental values was interpreted in terms of the basic structural units that constituting the glass network.     

Structure and Properties of SnO2–In2O3–Ag–N Coatings Formed by a Complex Method on Copper

Russian Physics Journal - The aim of this work is to analyze the structure and properties of a coating of the SnO2–In2O3–Ag–N composition formed on copper by a complex method...     

Theoretical analysis on phase behaviour of a liquid crystalline material – effect of molecular motions

Molecular structure, and phase behaviour of 2-Cyano-N-[4-(4-n-pentyloxybenzoyloxy)-benzylidene] aniline (CPBBA) has been reported with respect to translational and orientational motions. The atomic net charge and dipole moment components at each atomic centre have been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh–Schrodinger perturbation theory along with multicentered–multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for short-range interactions. The interaction energy values obtained through these computations have been used as input to calculate the configurational probability at room temperature (300 K), and nematic–isotropic transition temperature (396.5 K). On the basis of stacking, in-plane, and terminal interaction energy calculations, all possible geometrical arrangements between the molecular pairs have been considered. Molecular arrangements inside a bulk of materials have been discussed in terms of their relative order. Further, translational rigidity parameter has been estimated as a function of temperature to understand the phase behaviour of the compound. The present model is helpful to understand the effect of molecular motions on ordering, and phase behaviour of the mesogenic compounds.     

Structural and optical properties of WO3–PbO–B2O3 glass-ceramic

The WO₃–PbO–B₂O₃ glasses and glass ceramics are prepared and investigated with the help of XRD, density, molar volume, UV–visible and FTIR spectroscopy. XRD pattern reveals the glassy behavior up to 4% concentration of WO₃ and ceramic behavior of the prepared samples with concentration of WO₃ >4%. Band gap of glass samples decreases with increase in the WO₃ concentration from 0–5%. The samples with WO₃ concentration >5% do not respond to UV–visible absorption. The density and molar volume measurements show the compaction of structure of the samples, which is due to the formation of BO₄ groups. FTIR spectroscopy shows the formation of BO₄ group and W–O–W bending vibration at high concentration of WO₃.     

Rashba spin–orbit effect on the magnetocapacitance of a 2DEG in a diluted magnetic semiconductor

We investigate the magnetocapacitance of the two-dimensional electron gas (2DEG) embedded in diluted magnetic semiconductors in the presence of Rashba spin–orbit interaction (SOI). We present calculations on the energy spectrum and density of states and show that the tunable spin–orbit coupling and the enhanced Zeeman splitting have a strong effect on the magnetocapacitance of the structure. In the presence of Rashba SOI, a typical beating pattern with well defined node-positions in the oscillating capacitance is observed. A simple relation that predicts the positions of nodes in the beating patterns is obtained. The interplay between the total Zeeman splitting (including the s–d exchange interaction) and the Rashba SOI is discussed.     

Methanol-driven structuring of Au–Pt bimetallic nanoclusters on a thin film of Al2O3/NiAl(100)

The adsorption of methanol altered structures of Au–Pt bimetallic nanoclusters on a thin film of Al₂O₃/NiAl(100). Methanol adsorbed on the Au–Pt intermixed bimetallic clusters, of which the surfaces consist of both Au and Pt, induced a segregation of Au from Pt. This segregation state was unstable, as the clusters returned to the initial Au–Pt intermixed state upon desorption or decomposition of adsorbed methanol. Ethanol and cyclohexene were adsorbed on Au–Pt bimetallic clusters for comparisons, indicating that the interaction of the hydroxyl group of methanol with the clusters accounts for the structural modifications.     

Theoretical study of the microscopic Doppler effect for energetic material

We develop a physical model to describe the microscopic Doppler effect of phonon states in energetic material and use it to investigate the phonon–strain scattering behaviour of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. The required elastic constants and force constants are obtained by first-principles calculations. By using the phonon–strain scattering probability, a set of dissipation parameters are calculated, such as the viscosity coefficient, damping rate of elastic wave, and heat dissipation across shock wave front. It is interesting that the Doppler effect could describe the microscopic phonon scattering mechanism reasonably.     

Microwave-assisted synthesis of Zn–WO3 and ZnWO4 for pseudocapacitor applications

Nanosized Zn–WO₃ and ZnWO₄ materials have been prepared by microwave irradiation method. The physico-chemical characterization of the prepared nanomaterials was carried out by X-ray diffraction (XRD) and high resolution-scanning electron microscopy (HR-SEM) techniques. The size and shape of the ZnWO₄ material can be controlled by changing the temperature. The XRD analysis revealed the formation of monoclinic phase of the calcined nanopowder. The HR-SEM images showed the sphere and plate shape particles. The electrochemical behavior of the ZnWO₄ modified electrodes was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques. The synthesized material shows the pseudocapacitance. The specific capacitance of 35.70 F/g was achieved for the Zn–WO₃ nanopowder.     

Wall effect on fluid–structure interactions of a tethered bluff body

Wind tunnel experiments have shown an unexplained amplification of the free motion of a tethered bluff body in a small wind tunnel relative to that in a large wind tunnel. The influence of wall proximity on fluid–structure interaction is explored using a compound pendulum motion in the plane orthogonal to a steady freestream with a doublet model for aerodynamic forces. Wall proximity amplifies a purely symmetric single degree of freedom oscillation with the addition of an out-of-phase force. The success of this simple level of simulation enables progress to develop metrics for unsteady wall interference in dynamic testing of tethered bluff bodies.     

The effect of metal work function on the barrier height of metal/CdS/SnO2/In–Ga structures

In order to interpret the effect of metal work function on the formation of the barrier height at metal/semiconductor (M/S) interface, the CdS/SnO₂/In–Ga structures with several metals (Ag, Au, Al, Te) have been investigated by using I–V characteristics at room temperature. The main electrical parameters such as ideality factor (n), zero-bias barrier height (Φ_Bo), series resistance (R_s) have been determined and compared with each other. The values of n were found to be 3.00, 2.56, 3.83, and 3.31 for Al, Ag, Te, and Au/CdS/SnO₂/In–Ga structures, respectively. The values of Φ_Bo were also found to be 0.489 eV, 0.490 eV, 0.583 eV, 0.591 eV for Al, Ag, Te, and Au/CdS/SnO₂/In–Ga structures, respectively. The Φ_Bo dependence on the metal work function (Φ_m) was found to vary almost linearly as Φ_Bo = 0.106Φ_m + 0.028. The low value of the slope S (dΦ_B/dΦ_M ? 0.106) shows a weak relationship between Φ_Bo and Φ_m due to serious Fermi-level pinning in the conduction band. In addition, the I–V plots have a rectifying behavior. The rectification ratio, defined by the ratio of forward to reverse current (RR = I_F/I_R) measured at the same absolute bias, was found as 11.96, 20.88, 35.82, and 75.61 for Al, Ag, Te, Au/CdS/SnO₂/In–Ga diodes, respectively. In addition, the values of R_s were determined from Ohm's Law and Norde's method. Analysis of I–V characteristics confirm that using of different metal (Al, Ag, Te, Au) has significant effect on electrical parameters of such devices.     

Facile synthesis of SnO2–ZnO core–shell nanowires for enhanced ethanol-sensing performance

The design of core–shell heteronanostructures is powerful tool to control both the gas selectivity and the sensitivity due to their hybrid properties. In this work, the SnO₂–ZnO core–shell nanowires (NWs) were fabricated via two-step process comprising the thermal evaporation of the single crystalline SnO₂ NWs core and the spray-coating of the grainy polycrystalline ZnO shell for enhanced ethanol sensing performance. The as-obtained products were investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence. The ethanol gas-sensing properties of pristine SnO₂ and ZnO–SnO₂ core–shell NW sensors were studied and compared. The gas response to 500 ppm ethanol of the core–shell NW sensor increased to 33.84, which was 12.5-fold higher than that of the pristine SnO₂ NW sensor. The selectivity of the core–shell NW sensor also improved. The response to 100 ppm ethanol was about 14.1, whereas the response to 100 ppm liquefied petroleum gas, NH₃, H₂, and CO was smaller, and ranged from 2.5 to 5.3. This indicates that the core–shell heterostructures have great potential for use as gas sensing materials.     

Method for preparing a novel type of Pt–carbon fiber disk ultramicroelectrode

A novel and facile method has been developed for the fabrication of Pt–carbon fiber (Pt/CF) disk ultramicroelectrode (DUME). This method, which might be a simple and economical shortcut to get access to Pt/CF DUME, is based upon having metal Pt electroplated on CF DUME. In this paper, an electrode prepared through the new way was characterized by cyclic voltammetry and applied as probe for scanning electrochemical microscope.     

Radiation effect of neutrons produced by D–D side reactions on a D–3He fusion reactor

One of the most important characteristics in D–³He fusion reactors is neutron production via D–D side reactions. The neutrons can activate structural material, degrading them and ultimately converting them into high-level radioactive waste, while it is really costly and difficult to remove them. The neutrons from a fusion reactor could also be used to make weapons-grade nuclear material, rendering such types of fusion reactors a serious proliferation hazard. A related problem is the presence of radioactive elements such as tritium in D–³He plasma, either as fuel for or as products of the nuclear reactions; substantial quantities of radioactive elements would not only pose a general health risk, but tritium in particular would also be another proliferation hazard. The problems of neutron radiation and radioactive element production are especially interconnected because both would result from the D–D side reaction. Therefore, the presentation approach for reducing neutrons via D–D nuclear side reactions in a D–³He fusion reactor is very important. For doing this research, energy losses and neutron power fraction in D–³He fusion reactors are investigated. Calculations show neutrons produced by the D–D nuclear side reaction could be reduced by changing to a more ³He-rich fuel mixture, but then the bremsstrahlung power loss fraction would increase in the D–³He fusion reactor.     

A novel approach to a Brillouin–LIDAR for remote sensing of the ocean temperature

Ocean temperature profiles are of great importance in oceanography. For instance, an efficient remote sensing measurement technique of these profiles will facilitate climate studies and improvements in weather forecast. In this paper we describe developments towards a practical implementation of a Brillouin–LIDAR system capable of measuring temperature profiles in the ocean. In particular, we focus on our recent work on fiber amplifiers and a receiver unit based on a Faraday anomalous dispersion optical filter. PACS 42.79.Qx; 42.60.By; 42.62.Fi; 42.68.Xy; 42.50.Nn     

Structural Behavior of Pt–Sn Supported on MgO

Pt–Sn supported on magnesia and alumina were characterized, before and after treatment with hydrogen, by Mössbauer spectroscopy and X-ray diffraction. For the calcined samples on both supports tin is present as SnO₂ and platinum as metal. After reduction with hydrogen, platinum and tin diffuse into the magnesia lattice to form a solid solution. On alumina Sn(IV), Sn(II), Sn(0), Pt, Pt₃Sn, PtSn and PtSn₂ alloys are formed. The SnO interacts strongly with the alumina support. The catalytic activity of both Pt–Sn catalysts is strongly affected by the support. On alumina the dehydrogenation of cyclohexane is very high, whereas that on magnesia is almost non-active.     

Room temperature hydrogen sensing of multiple networked ZnO/WO3 core–shell nanowire sensors under UV illumination

ZnO/WO₃ core–shell nanowires were synthesized by thermal evaporation of a mixture of ZnO and graphite powders (ZnO:C = 1:1) followed by sputter-deposition of WO₃. The sensing properties of multiple networked ZnO-core/WO₃-shell nanorod sensors toward H₂ gas was examined. The responses of pristine ZnO and ZnO-core/WO₃-shell nanorods to 1000 ppm H₂ at room temperature under UV illumination were ∼236% and ∼645%, respectively. The responses of the core–shell nanowires increased from ∼118 to ∼645% with increasing the UV illumination intensity from 0 mW/cm² to 1.2 mW/cm². The enhanced sensing performance of the ZnO-core/WO₃-shell nanowires induced by encapsulation with WO₃ was explained based on a combination of surface depletion and potential barrier-controlled carrier transport models. The origin of the enhanced sensing properties of ZnO-core/WO₃-shell nanorods toward H₂ under UV illumination was also discussed.     

Effect of phosphorus and copper additions on the structure of Pt and Pt–Cu nanoparticles in a radiation-induced reduction method

A facile chemical process has been developed for the preparation of magnetic FeCo nanoparticles. The FeCo nanoparticles were mono-dispersed, obtained by the safe and ecofriendly method, possessed saturation magnetization up to 187 emu/g, and demonstrated excellent chemical stability. In this work, we have studied how to control Fe/Co ratio by variation of precursor ratio, and how to vary particle size from 9.3 to 12.3 nm by surfactant amount used. The cytotoxicity of as-synthesized nanoparticles was investigated after coating with the poly(methyl methacrylate-co-butyl acrylate) by the emulsion process and the results demonstrated high biocompatibility. Similarly, the same synthesis method was used with the single precursor FeO(OH) or Co₃O₄. The results showed that this method can also fabricate 10 nm mono-dispersed spherical Fe₃O₄ particles and self-assembly Co nanoneedles.     

Electronic structures of CO adsorbed Pt-skin surface on Pt–Co and Pt–Ni alloys

By using angle resolved photoemission spectroscopy, we investigate the electronic structures of Pt-skin layer of Pt–Co and Pt–Ni alloys with CO molecules on the surface. Measured Fermi surface maps and band dispersions reflect the signatures of chemical bonding between Pt-skin layer and CO molecules. Furthermore, the degree of chemical bonding strength of CO molecules, estimated from the energy shift of the participating bands, is found to be reduced on both Pt bimetallic alloys. Our results show how the surface band structure of Pt bimetallic alloys is modified with molecular orbitals of CO molecules on the surface, revealing the important role of the electronic structure in the determination of chemical properties of bimetallic alloys.