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Acoustical Physics     Hybrid Journal   (8 followers)
Acoustics Today     Hybrid Journal   (2 followers)
Acta Acustica united with Acustica     Full-text available via subscription   (7 followers)
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Advanced Materials     Hybrid Journal   (199 followers)
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Advances in Condensed Matter Physics     Open Access   (6 followers)
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Advances In Physics     Hybrid Journal   (6 followers)
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Advances in Synchrotron Radiation     Hybrid Journal   (1 follower)
AIP Advances     Open Access   (4 followers)
American Journal of Applied Sciences     Open Access   (27 followers)
American Journal of Condensed Matter Physics     Open Access   (2 followers)
Analysis and Mathematical Physics     Hybrid Journal   (2 followers)
Annalen der Physik     Hybrid Journal   (2 followers)
Annales Geophysicae (ANGEO)     Open Access   (3 followers)
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Annual Review of Analytical Chemistry     Full-text available via subscription   (8 followers)
Annual Review of Condensed Matter Physics     Full-text available via subscription   (1 follower)
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Axioms     Open Access  
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Bulletin of Materials Science     Open Access   (34 followers)
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Cells     Open Access  
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Computational Materials Science     Hybrid Journal   (15 followers)

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Advances in Condensed Matter Physics    [8 followers]  Follow    
  This is an Open Access Journal Open Access journal
     ISSN (Print) 1687-8108 - ISSN (Online) 1687-8124
     Published by Hindawi Publishing Corporation Homepage  [347 journals]   [SJR: 0.6]   [H-I: 7]
  • Larmor Precession and Debye Relaxation of Single-Domain Magnetic
    • Abstract: The numerous phenomenological equations used in the study of the behaviour of single-domain magnetic nanoparticles are described and some issues clarified by means of qualitative comparison. To enable a quantitative application of the model based on the Debye (exponential) relaxation and the torque driving the Larmor precession, we present analytical solutions for the steady states in presence of circularly and linearly polarized AC magnetic fields. Using the exact analytical solutions, we can confirm the insight that underlies Rosensweig’s introduction of the “chord” susceptibility for an approximate calculation of the losses. As an important consequence, it can also explain experiments, where power dissipation for both fields was found to be identical in “root mean square” sense. We also find that this approximation provides satisfactory numerical accuracy only up to magnetic fields for which the argument of the Langevin function reaches the value 2.8.
      PubDate: Thu, 23 Jan 2014 16:17:50 +000
  • Nanostructure and Optical Properties of Silver Helical Pentagon
           Nanosculptured Thin Films
    • Abstract: Silver helical pentagon shaped nanosculptured thin films (HPNSTFs) were produced using oblique angle deposition method in conjunction with the rotation of sample holder under controlled conditions. The -polarization extinction spectra obtained at different azimuthal angles () and low incidence angle (i.e., ) from the Ag (HPNSTF) did not show significant change in the plasmon peak position, while at higher incidence angle (i.e., ) a blue shift appeared for the broad peak which was observed for lower incidence angle (i.e., ) and occurred at lower wavelength. In case of -polarized light a very broad peak was obtained for the incidence angle and for different angles and when compared with the lower incidence angle results it can be concluded that it is gone under a red shift. Polar diagrams of the samples showed slight anisotropy that should be due to high symmetry of the pentagon helical structure.
      PubDate: Mon, 20 Jan 2014 09:51:12 +000
  • Phase- and Polarization-Controlled Two-Photon Rabi Oscillation of the
           Biexciton State in a Semiconductor Quantum Dot
    • Abstract: Under a degenerate two-photon resonant excitation, the Rabi oscillation of the four-level biexciton system in a semiconductor quantum dot is theoretically investigated. The influence of the laser phases on the state manipulation is modeled and numerically calculated. Due to the interference between different excitation paths, the laser phase plays an important role and can be utilized as an alternate control knob to coherently manipulate the biexciton state. The phase control can be facilely implemented by changing the light polarization via a quarter-wave plate.
      PubDate: Sun, 19 Jan 2014 11:30:19 +000
  • Numerical Analysis of Oxygen Adsorption on SnO2 Surface Using Slab
    • Abstract: Oxidation of thin film SnO2 layer was simulated. In particular, the evolution of depletion layer was investigated by solving Poisson-Boltzmann equation for SnO2 slab geometry grains. On this basis, the surface energy barrier dependence on layer thickness (30–500 nm) was obtained. The effect of the donor mobility (oxygen vacancies in the bulk) and degree of donor ionization on electric potential inside layer with different thicknesses was discussed. Furthermore, the dependence of per-square conductance on temperature (from 400 K to 700 K) has been computed. It was assumed that the bulk oxygen vacancies (donors) are singly or doubly ionized and mobile. The temperature variations in the carrier mobility were also taken into account.
      PubDate: Thu, 16 Jan 2014 10:06:05 +000
  • Structural, Optical, and Compactness Characteristics of Nanocrystalline
           Synthesized through an Autoigniting Combustion Method
    • Abstract: Nanoparticles of calcium metaniobate compound are prepared by an autoigniting combustion technique and its structural, optical, and dielectric properties are investigated. The X-ray diffraction, Fourier-transform Raman, and infrared studies reveal that calcium metaniobate possesses phase pure orthorhombic columbite structure with space group of Pbcn. The average particle size of the as-prepared nanoparticles obtained from both the Scherrer formula and transmission electron microscopy is ~37 nm. The optical band gap calculated from Tauc's Plot is 3.25 eV. Photoluminescence studies reveal that Calcium metaniobate can be used as an idealphotoluminarmaterial. The powders are pelletised and sintered at an optimized temperature of in a short duration of two hours, yielding a high density. The morphology of the sintered pellet is further examined using scanning electron microscopy. The dielectric constant and loss factor values measured at 5 MHz for a well-sintered Calcium metaniobate pellet are found to be 27.6 and respectively, at room temperature.
      PubDate: Thu, 09 Jan 2014 16:17:56 +000
  • Investigation on Growth, Structural, Spectral, Optical, and Mechanical
           Properties of an Organic Nonlinear Optical Material: Morpholinium Hydrogen
    • Abstract: Organic nonlinear optical crystal morpholinium hydrogen tartrate (MHT), with molecular formula [C8H15NO7], has been grown by slow evaporation solution technique. Single crystal X-ray diffraction study confirms that MHT crystallizes in orthorhombic system with noncentrosymmetric space group P212121. FTIR spectrum was recorded to identify the various functional groups of MHT. The various kinds of protons and carbons of MHT have been identified using 1H and 13C NMR spectral analyses. The range of optical absorption was ascertained by recording UV-Vis-NIR spectral studies. The TG/DTA studies revealed that the grown crystal is thermally stable up to 159.26°C. The mechanical property of the grown crystal was studied using Vickers microhardness studies. The relative second harmonic generation efficiency of MHT was determined using Kurtz and Perry powder technique; it was observed to be greater than that of KDP crystal.
      PubDate: Sun, 05 Jan 2014 07:46:59 +000
  • Size Effects on Surface Elastic Waves in a Semi-Infinite Medium with
           Atomic Defect Generation
    • Abstract: The paper investigates small-scale effects on the Rayleigh-type surface wave propagation in an isotopic elastic half-space upon laser irradiation. Based on Eringen’s theory of nonlocal continuum mechanics, the basic equations of wave motion and laser-induced atomic defect dynamics are derived. Dispersion equation that governs the Rayleigh surface waves in the considered medium is derived and analyzed. Explicit expressions for phase velocity and attenuation (amplification) coefficients which characterize surface waves are obtained. It is shown that if the generation rate is above the critical value, due to concentration-elastic instability, nanometer sized ordered concentration-strain structures on the surface or volume of solids arise. The spatial scale of these structures is proportional to the characteristic length of defect-atom interaction and increases with the increase of the temperature of the medium. The critical value of the pump parameter is directly proportional to recombination rate and inversely proportional to deformational potentials of defects.
      PubDate: Mon, 30 Dec 2013 14:31:48 +000
  • Nb Substitution Effects on Superconducting Properties of
    • Abstract: In order to gain further insight into the role of substitution of Ru by Nb on superconductivity, polycrystalline samples of Ru1−xNbxSr2Eu1.4Ce0.6Cu2O10−δ  (0.0 ≤ x ≤ 1.0) have been synthesized by solid-state reaction method. Substitution of Nb at the Ru site in the system takes place isostructurally in the tetragonal structure (space group I4/mmm) with full solubility (x = 1.0). Superconductivity exists for all compositions. Resistivity measurements in function of temperature from 0 to 300 K were done using the four-probe technique. It is found that the substitution of Ru5+ for Nb5+ depresses the superconductivity of samples from  = 29 K for x = 0.0 to  = 5 K for x = 1.0 (where is the critical temperature, when resistivity becomes equal to zero). In the normal state, the dependence of resistivity with temperature, for compositions with x = 0.0 and 0.2, shows a metallic behavior, while for compositions between x = 0.4 and x = 1 it shows a semiconducting behavior. In that way, the density of charge carriers is reduced with niobium doping, leading to the semiconducting behavior. The resistive transition to the superconducting state of all samples is found to be affected by granularity. Samples undergo double superconducting transition.
      PubDate: Sat, 28 Dec 2013 12:00:38 +000
  • Study on the Macromesoscopic Yield Criterion of Concrete Material
    • Abstract: In mesoscopy, the concrete material is a kind of composite consisting of mortar matrix, aggregate, and the interface between them. And the shape of aggregate is assumed to be spherical and the mortar matrix is supposed to satisfy the Drucker-Prager yield criterion. The energy density support function is introduced to reflect the yield surface of mortar matrix. In order to solve the nonderivability on the yield boundary, the function approximation series has been constructed to substitute for the energy density support function. Finally, based on the function series, a macromesoscopic yield criterion of concrete material has been derived by the nonlinear homogenized technique. Through the macromesoscopic yield criterion established, the influence law of the bonding status of interface and the fraction of aggregate on the macrofriction coefficient is explored.
      PubDate: Thu, 26 Dec 2013 13:33:32 +000
  • Synthesis, Tunable Multicolor Output, and High Pure Red Upconversion
           Emission of Lanthanide-Doped Lu2O3 Nanosheets
    • Abstract: Yb3+ and Ln3+ (Ln = Er, Ho) codoped Lu2O3 square nanocubic sheets were successfully synthesized via a facile hydrothermal method followed by a subsequent dehydration process. The crystal phase, morphology, and composition of hydroxide precursors and target oxides were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray spectroscope (EDS). Results present the as-prepared Lu2O3 crystallized in cubic phase, and the monodispersed square nanosheets were maintained both in hydroxide and oxides. Moreover, under 980 nm laser diode (LD) excitation, multicolor output from red to yellow was realized by codoped different lanthanide ions in Lu2O3. It is noteworthy that high pure strong red upconversion emission with red to green ratio of 443.3 of Er-containing nanocrystals was obtained, which is beneficial for in vivo optical bioimaging.
      PubDate: Mon, 23 Dec 2013 09:01:56 +000
  • Temperature Dependence of Electrical Properties and Crystal Structure of
           0.29Pb(In1/2Nb1/2)O3–0.44Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 Single
    • Abstract: We characterized the temperature dependent (25–200°C) electromechanical properties and crystal structure of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals using in situ electrical measurement and neutron diffraction techniques. The results show that the poled crystal experiences an addition phase transition around 120°C whereas such a transition is absent in the unpoled crystal. It is also found that the polar order persists above the maximum dielectric permittivity temperature at which the crystal shows a well-defined antiferroelectric behavior. The changes in the electrical properties and underlying crystal structure are discussed in the paper.
      PubDate: Sun, 22 Dec 2013 18:13:30 +000
  • A Facile Synthesis and Optical Properties of Bundle-Shaped
           TbPO4·H2O Nanorods
    • Abstract: Bundle-shaped TbPO4·H2O nanorods have been prepared by a facile hydrothermal technique and characterized by XRD, SEM, TEM, UV-Vis diffuse reflectance spectrum (DRS), photoluminescence (PL) spectrum, and lifetime. The results indicate that the obtained sample has hexagonal structure of TbPO4·H2O and is composed of nanorods bundles which is assembled from many single crystalline nanorods with the diameter of around 45 nm and the length of 2.3 μm. The growth of the single crystalline nanorod is along the (001) plane direction. Under the UV light irradiation, TbPO4·H2O nanorods bundles exhibit bright green emission corresponding to the () transitions of the Tb3+ ions, and the lifetime is determined to be about 0.24 ms.
      PubDate: Wed, 18 Dec 2013 15:45:54 +000
  • Relativistic Fermion on a Ring: Energy Spectrum and Persistent Current
    • Abstract: The energy and persistent current spectra for a relativistic fermion on a ring are studied in detail. The nonlinear nature of persistent current in relativistic regime and its dependence on particle mass and ring radius are analysed thoroughly. For a particular ring radius, we find the existence of a critical mass at which the single ring current does not depend on the flux. In lower mass regime, the total current spectrum shows plateaus at different height which appears periodically. The susceptibility as well shows periodic nature with amplitude depending on particle mass. As we move from higher mass to lower mass regime, we find that the system turns into paramagnetic from diamagnetic. We also show that same behaviour is observed if one vary the radius of the ring for a fixed particle mass. Hence the larger ring will be diamagnetic while the smaller one will be paramagnetic. Finally we propose an experiment to verify our findings.
      PubDate: Tue, 17 Dec 2013 15:52:25 +000
  • Modelling of Dual-Junction Solar Cells including Tunnel Junction
    • Abstract: Monolithically stacked multijunction solar cells based on III–V semiconductors materials are the state-of-art of approach for high efficiency photovoltaic energy conversion, in particular for space applications. The individual subcells of the multi-junction structure are interconnected via tunnel diodes which must be optically transparent and connect the component cells with a minimum electrical resistance. The quality of these diodes determines the output performance of the solar cell. The purpose of this work is to contribute to the investigation of the tunnel electrical resistance of such a multi-junction cell through the analysis of the current-voltage (J-V) characteristics under illumination. Our approach is based on an equivalent circuit model of a diode for each subcell. We examine the effect of tunnel resistance on the performance of a multi-junction cell using minimization of the least squares technique.
      PubDate: Mon, 16 Dec 2013 09:32:11 +000
  • Synthesis and Downconversion Emission Property of : Nanosheets and
    • Abstract: Ytterbium oxide (Yb2O3) nanocrystals with different Eu3+ (1%, 2%, 5%, and 10%) doped concentrations were synthesized by a facile hydrothermal method, subsequently by calcination at 700°C. The crystal phase, size, and morphology of prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the as-prepared Yb2O3 nanocrystals with sheet- and tube-like shape have cubic phase structure. The Eu3+ doped Yb2O3 nanocrystals were revealed to have good down conversion (DC) property and intensity of the DC luminescence can be modified by Eu3+ contents. In our experiment the 1% Eu3+ doped Yb2O3 nanocrystals showed the strongest DC luminescence among the obtained Yb2O3 nanocrystals.
      PubDate: Sun, 15 Dec 2013 14:03:33 +000
  • Structural Disorder in the Key Lead-Free Piezoelectric Materials, and
    • Abstract: Using electron diffraction, trends in the local structural behaviour of the NNb (KNN x) and the (NBT-()BT) systems are investigated. In KNN, electron diffraction shows a single plane of diffuse intensity perpendicular to [010] across the entire phase diagram, indicating the existence of ferroelectric disorder along this axis. An additional characteristic pattern of diffuse scattering is also observed, involving rods of diffuse intensity running along the and directions of the perovskite substructure and indicative of octahedral tilt disorder about these axes. Similarly, in the NBT-xBT system, rods of diffuse intensity running along the directions of the perovskite substructure are observed, again indicating octahedral tilt disorder. Ferroelectric-like disorder is also observed in highly BT doped samples, and a continuous change from the “rhombohedral” structure of NBT to the “tetragonal” structure of NBT-12BT is seen from characteristic variation in observed superstructure reflections. A crystal chemical rationalisation of these results is performed, and the implications for structure and properties are discussed.
      PubDate: Mon, 09 Dec 2013 14:35:02 +000
  • Shape and Size Dependence of Electronic Properties of InSb Diamondoids and
           Nanocrystals: A Density Functional Theory Study
    • Abstract: Shape and size dependence of electronic properties of InSb diamondoids and nanocrystals is investigated using density functional theory. Cluster and large unit cell methods are combined with molecular orbital methods to obtain electronic structure of InSb diamondoids and nanocrystals. Starting from the simple molecules of hydrogenated InSb clusters such as InSbH6, In3Sb3H12, InSb-diamantane, InSb-tetramantane, and InSb-hexamantane and ending with InSb large unit cell method we were able to obtain the electronic structure of a wide range of InSb nanostructures. Results showed that energy gap and In–Sb bond lengths generally decrease as the number of atoms increases with remarkable dependence on the shape of the molecule or nanocrystal. Atomic charges, tetrahedral angles, and bond lengths are used to compare different sizes, locations, and shapes of InSb diamondoids and nanocrystals.
      PubDate: Mon, 09 Dec 2013 08:55:48 +000
  • The Influence of Surface Morphology of Buffer Layer on the Critical
           Current Density in YBCO Coated Conductors
    • Abstract: 1 m-thick (YBCO) films were grown on the Y2O3/yttria stabilized zirconia (YSZ)/CeO2 buffer layers with different surface morphologies using direct-current sputtering. The critical current density () value of YBCO was 1.1 MA/cm2 when the root mean square surface roughness () of the buffer layer was 2.5 nm. As the of the buffer layer increased to 15 nm, the decreased to 0.3 MA/cm2. X-ray diffraction and scanning electron microscopy showed the strong relevance of the evolution of the structure and surface morphologies of YBCO films with the buffer layer of different . A model was proposed to explain the influence of surface morphology on the superconducting properties of YBCO films.
      PubDate: Wed, 04 Dec 2013 18:36:49 +000
  • Decomposition and Oriented Growth of Films Prepared with Low Fluorine
           TFA-MOD Approach
    • Abstract: TFA-MOD approach of (YBCO) films has been approved to be the most promising method for mass production of low cost high temperature coated conductors. In order to reduce the decomposition time and improve the properties of YBCO films, copper propionate was used as the precursor and certain Lewis-bases were introduced into the precursor solution. The fluorine content of the solution was significantly reduced. High quality oriented YBCO films were prepared on LAO substrates with this low fluorine TFA-MOD approach. The effects of the sintering temperature on the oriented growth and properties of YBCO films were investigated. The preliminary results yielded the critical current density () of 2 MA/cm2 and critical current () of 120 A/cm width at 77 K and self-field.
      PubDate: Wed, 04 Dec 2013 14:09:26 +000
  • Electrical Transport Properties of (Bi1.6Pb0.4Sr2Ca2Cu3O10)/Ag Tapes with
           Different Nanosized MgO
    • Abstract: MgO nanopowders with average size 20 and 40 nm were introduced into (Bi1.6Pb0.4Sr2Ca2Cu3O10)(MgO)x ( wt.%) in the pellet form. The optimum amounts for the highest transport critical current density were and 0.01 wt.% for 20 and 40 nm MgO, respectively. These results were used to fabricate MgO added (Bi, Pb)-2223/Ag sheathed tapes using the powder-in-tube method. The tapes were sintered at 845°C for 50 h and 100 h. The structure, microstructure, and of the tapes were determined. The temperature and magnetic field dependence of for the MgO added tapes exhibited a significant enhancement compared with the nonadded tapes. of 20 nm MgO added tape was higher compared with the 40 nm MgO added tape. A higher was obtained when the tapes were sintered for 100 h. The increase in can be explained as the increase of the flux pinning strength by nanosized MgO. The nanoparticle with size closer to the coherence length was more effective in enhancing .
      PubDate: Tue, 03 Dec 2013 15:15:35 +000
  • Hydrothermal Synthesis and Tunable Multicolor Upconversion Emission of
           Cubic Phase Y2O3 Nanoparticles
    • Abstract: Highly crystalline body-centered cubic structure Y2O3 with lanthanide (Ln) codopants (Ln = Yb3+/Er3+ and Yb3+/Ho3+) has been synthesized via a moderate hydrothermal method in combination with a subsequent calcination. The structure and morphology of Y(OH)3 precursors and Y2O3 nanoparticles were characterized by X-ray diffraction and transmission electron microscopy. The results reveal that the Y2O3 nanoparticles possess cubic phase and form the quasispherical structure. The upconversion luminescence properties of Y2O3 nanoparticles doped with different Ln3+ (Yb3+/ Er3+ and Yb3+/ Ho3+) ions were well investigated under the 980 nm excitation. The results show that the Yb3+/Er3+ and Yb3+/Ho3+ codoped Y2O3 nanoparticles exhibit strong red and light yellow upconversion emissions, respectively. It is expected that these Y2O3 nanoparticles with tunable multicolor output and intense red upconversion emission may have potential application in color displays and biolabels.
      PubDate: Tue, 03 Dec 2013 13:39:02 +000
  • Electrical Properties of Amorphous Titanium Oxide Thin Films for
           Bolometric Application
    • Abstract: We report the electrical conduction mechanism of amorphous titanium oxide thin films applied for bolometers. As the O/Ti ratio varies from 1.73 to 1.97 measured by rutherford backscattering spectroscopy, the resistivity of the films increases from 0.26  cm to 10.1  cm. At the same time, the temperature coefficient of resistivity and activation energy vary from −1.2% to −2.3% and from 0.09 eV to 0.18 eV, respectively. The temperature dependence of the electrical conductivity illustrates a thermally activated conduction behavior and the carrier transport mechanism in the titanium oxide thin films is found to obey the normal Meyer-Neldel Rule in the temperature range from 293 K to 373 K.
      PubDate: Sat, 30 Nov 2013 18:31:12 +000
  • Intense Red Upconversion Emission and Shape Controlled Synthesis of
           Gd2O3:Yb/Er Nanocrystals
    • Abstract: Yb/Er codoped Gd(OH)3 was synthesized firstly via a simple hydrothermal treatment of the corresponding nitrate in the presence of alkali by tuning the pH values. The Gd2O3:Yb/Er nanocrystals were obtained via sintering the corresponding hydroxides precursors. The as-prepared samples were characterized by the typical X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), high-resolution TEM, and spectrophotometer. The results revealed that two shapes of the as-prepared Gd2O3:Yb/Er nanocrystals can be readily tuned from lemon-like particle to rod-like structure via tuning pH values from 7 to 14. Moreover, compared with the samples prepared at pH 7, the Gd2O3:Yb/Er nanocrystals prepared at pH 14 exhibit enhanced red upconversion emission and higher upconversion luminescence intensity under the excitation of 980 nm laser.
      PubDate: Mon, 25 Nov 2013 10:31:05 +000
  • Topological Excitations in Quantum Spin Systems
    • Abstract: The origin and significance of topological excitations in quantum spin models in low dimensions are presented in detail. Besides a general review, our own work in this area is described in great depth. Apart from theoretical analysis of the existence and properties of spin vortices and antivortices, the possible experimental consequences and signatures are also highlighted. In particular, the distinguishing features between the even and odd charged topological excitations are brought out through a detailed analysis of the topological term in the quantum action. Moreover, an interesting symmetry property is predicted between the excitations from a ferromagnetic model and an antiferromagnetic model. Through a novel approach of ours, a bridge is established between field theoretical formalism and the well-known statistical mechanical treatment of Berezinskii-Kosterlitz-Thouless (BKT) transition involving these topological excitations. Furthermore, a detailed phenomenological analysis of the experimentally observed static and dynamic magnetic properties of the layered magnetic materials, possessing XY anisotropy in the in-plane spin-spin couplings, is undertaken to test the theoretical predictions regarding the behaviour of these excitations. The importance and the crucial role of quantum spin fluctuations in these studies are also brought out very clearly by our analysis.
      PubDate: Thu, 21 Nov 2013 13:47:17 +000
  • Phase Transition and Optical Properties for Ultrathin KNbO3 Nanowires
    • Abstract: Fascicular KNbO3 nanowires with tetragonal perovskite structures and ultrasmall diameters are synthesized by hydrothermal route at about 150°C for 24 hours. The concentrations of medium alkalinity have influenced phase structures and the final morphologies of the products significantly by modifying the conditions in process. The as-prepared KNbO3 nanowires exhibit three phase transitions at about 343, 454.7, and 623 K as the temperature increases from 250 to 700 K. The band gap is about 3.78 eV for KNbO3 nanowires. Photoluminescence study at room temperature reveals two visible light emission bands peaking at ~551 and 597 nm, respectively, which may be due to the oxygen vacancies, site niobium (occupy the location of Nb), and antisite niobium (occupy the location of K) in KNbO3 nanowires.
      PubDate: Thu, 21 Nov 2013 10:53:30 +000
  • Dielectric Properties of Φ(BZT-BCT)-(1−Φ) Epoxy
           Composites with 0-3 Connectivity
    • Abstract: Lead free ferroelectric ceramic [0.5[Ba(Zr0.2Ti0.8)O3]-0.5[(Ba0.7Ca0.3)TiO3]]/(BZT-BCT)-epoxy composites with 0-3 connectivity (particles connected in 3 dimensions) were prepared using hand lay-up technique followed by cold pressing for different volume fractions of (BZT-BCT) ceramic powder in the epoxy polymer matrix. The structural, microstructural, and dielectric properties of the composites have been investigated and discussed. XRD studies revealed the presence of both ceramic and polymer phases in the (BZT-BCT)-epoxy composites. SEM studies showed a uniform distribution of ceramic particles in the epoxy matrix, which confirmed the 0-3 connectivity in the composites. Dielectric studies revealed an increase in relative permittivity () and decrease in dielectric loss () in the composites with the increase in the volume fractions of the ceramics up to 20%. This can be ascribed to the increase in density of the composites and dielectric properties of the epoxy polymer. At room temperature (RT) and at 1 kHz frequency, 0.2(BZT-BCT)-0.8(epoxy) composite showed the highest relative permittivity . For the prediction of the effective dielectric constant of the composites, the experimental data were fitted to several theoretical equations. Effective medium theory (EMT) model and Yamada models were found to be useful for the prediction of the effective dielectric constant of studied composites.
      PubDate: Wed, 20 Nov 2013 15:06:47 +000
  • Aging Effect on Electrical Conductivity of Pure and Al-Doped
           YBa2Cu3O7−δ Single Crystals with a Given Topology of Planar
    • Abstract: The conducting properties in the basal plane of pure and Al-doped single crystals before and after long-time exposure in air atmosphere are investigated. It is shown that prolonged aging leads to an increase of the density of effective scattering centers for the normal carriers. The aluminum doping has been revealed to partially slowdown the degradation of the conducting properties in process of aging. The excess conductivity, , has been found to obey exponential dependence in the broad temperature range . In the pseudogap regime, the mean-field transition temperature and the 3D-2D crossover point in the excess conductivity have been quantified. Near the critical temperature, is described well within the Aslamazov-Larkin theoretical model. Herewith, both aluminum doping and prolonged aging have been found to essentially expand the temperature interval of implementation of the pseudogap state, thus narrowing the linear section in the dependence .
      PubDate: Wed, 13 Nov 2013 11:20:39 +000
  • Photoreflectance Spectroscopy Characterization of Ge/Si0.16Ge0.84 Multiple
           Quantum Wells on Ge Virtual Substrate
    • Abstract: We report a detailed characterization of a Ge/Si0.16Ge0.84 multiple quantum well (MQW) structure on Ge-on-Si virtual substrate (VS) grown by ultrahigh vacuum chemical vapor deposition by using temperature-dependent photoreflectance (PR) in the temperature range from 10 to 300 K. The PR spectra revealed a wide range of optical transitions from the MQW region as well as transitions corresponding to the light-hole and heavy-hole splitting energies of Ge-on-Si VS. A detailed comparison of PR spectral line shape fits and theoretical calculation led to the identification of various quantum-confined interband transitions. The temperature-dependent PR spectra of Ge/Si0.16Ge0.84 MQW were analyzed using Varshni and Bose-Einstein expressions. The parameters that describe the temperature variations of various quantum-confined interband transition energies were evaluated and discussed.
      PubDate: Tue, 12 Nov 2013 08:42:48 +000
  • Diffusion-Limited Aggregation in Potato Starch and Hydrogen Borate
           Electrolyte System
    • Abstract: Natural growth of diffusion-limited aggregate (DLA), without any external stimuli, in boric acid doped starch system is reported here. Fractals grown were confirmed to be of diffusion-limited aggregate (DLA) pattern having fractal dimension ~1.49. Effect of substrate and humidity on growth pattern has also been discussed. The existence of a different vibration band of H3BO3 in FTIR confirmed that growth structures are related to boric acid. XRD pattern has shown broad peak along with some sharp peaks. Broad peak is related to starch’s amorphous nature, as where intense sharp peaks are due to boric acid.
      PubDate: Sun, 10 Nov 2013 08:58:29 +000
  • Simulation and Analysis of GaN Wafer Bowing on Sapphire Substrate
    • Abstract: During the process of heteroepitaxial growth, if the lattice constant of the growing film differs from that of the substrate, the wafer surface bows, regardless of whether the lattice mismatch occurs or not. As the growth in large-scale wafers speeds up, bowing effects are becoming more and more important. Wafer bowing has a direct impact on the yield in modern mass-production compound semiconductor industries. By using finite element analysis software, the bowing deformation of the GaN wafer on sapphire substrate can be studied. This paper summarizes the causes of bowing deformation, builds the mathematical model, and deduces the relation equation of the wafer bowing. The results show that epitaxial wafer bowing has a linear relationship with the square of the diameter of the substrate but has little relationship with the thickness of the substrate. Moreover, the relation equation of the wafer bowing is also simplified finally.
      PubDate: Thu, 07 Nov 2013 08:56:40 +000
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