White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved.

Electron mobility in few-layer MoxW1-xS2

Heterostructures of two-dimensional (2D) layered materials are increasingly being explored for electronics in order to potentially extend conventional transistor scaling and to exploit new device designs and architectures. Alloys form a key underpinning of any heterostructure device technology and therefore an understanding of their electronic properties is essential. In this paper, we study the intrinsic electron mobility in few-layer MoxW1-xS2 as limited by various scattering mechanisms. The room temperature, energy-dependent scattering times corresponding to polar longitudinal optical (LO) phonon, alloy and background impurity scattering mechanisms are estimated based on the Born approximation to Fermi's golden rule. The contribution of individual scattering rates is analyzed as a function of 2D electron density as well as of alloy composition in MoxW1-xS2. While impurity scattering limits the mobility for low carrier densities (<2-4x10(12) cm(-2)), LO polar phonon scattering is the dominant mechanism for high electron densities. Alloy scattering is found to play a non-negligible role for 0.5 < x < 0.7 in MoxW1-xS2. The LO phonon-limited and impurity-limited mobilities show opposing trends with respect to alloy mole fractions. The understanding of electron mobility in MoxW1-xS2 presented here is expected to enable the design and realization of heterostructures and devices based on alloys of MoS2 andWS(2).

In-plane modulated smectic (A)over-tilde vs smectic `A' lamellar structures in poly(ethyl or propyl ether imine) dendrimers

A pair of first and second generation poly(alkyl ether imine) dendrimers is prepared, having covalently attached cholesteryl moieties at their peripheries. The pairs in each generation differ in the alkyl-linker which constitute the dendritic core moieties, even when the number of cholesteryl moieties remains uniform in each pair. The dendrimer pairs are two first and second generation poly(ethyl ether imine) and poly(propyl ether imine) dendrimers, modified with 4 and 8 cholesteryl esters at the peripheries in each pair, respectively. The dendrimer pairs exhibit differing thermotropic mesophase properties. Microscopic, thermal and X-ray diffraction studies reveal a lamellar mesophase for the first generation ethyl-, first and second generation propyl-linker dendrimers. Whereas, the second generation ethyl-linker dendrimer exhibits a layered structure with a superimposed in-plane modulation, the length of which corresponds to a rectangular column width. The role of the dendrimer core moieties with differing linkers in modifying the mesophase properties is studied. (C) 2016 Elsevier Ltd. All rights reserved.

White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved.

Electron mobility in few-layer MoxW1-xS2

Heterostructures of two-dimensional (2D) layered materials are increasingly being explored for electronics in order to potentially extend conventional transistor scaling and to exploit new device designs and architectures. Alloys form a key underpinning of any heterostructure device technology and therefore an understanding of their electronic properties is essential. In this paper, we study the intrinsic electron mobility in few-layer MoxW1-xS2 as limited by various scattering mechanisms. The room temperature, energy-dependent scattering times corresponding to polar longitudinal optical (LO) phonon, alloy and background impurity scattering mechanisms are estimated based on the Born approximation to Fermi's golden rule. The contribution of individual scattering rates is analyzed as a function of 2D electron density as well as of alloy composition in MoxW1-xS2. While impurity scattering limits the mobility for low carrier densities (<2-4x10(12) cm(-2)), LO polar phonon scattering is the dominant mechanism for high electron densities. Alloy scattering is found to play a non-negligible role for 0.5 < x < 0.7 in MoxW1-xS2. The LO phonon-limited and impurity-limited mobilities show opposing trends with respect to alloy mole fractions. The understanding of electron mobility in MoxW1-xS2 presented here is expected to enable the design and realization of heterostructures and devices based on alloys of MoS2 andWS(2).

Hierarchically porous Li1.2Mn0.6Ni0.2O2 as a high capacity and high rate capability positive electrode material

Layered composite samples of lithium-rich manganese oxide (Li1.2Mn0.6Ni0.2O2) are prepared by a reverse microemutsion route employing a soft polymer template and studied as a positive electrode material. The product samples possess dual porosity with distribution of pores at 3.5 and 60 nm. Pore volume and surface area decrease on increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity value of the samples prepared at 800 and 900 degrees C is about 240 mA h g(-1) at a specific current of 25 mA g(-1) with a good cycling stability. The composite sample heated at 900 degrees C possesses a high rate capability with a discharge capacity of 100 mA h g(-1) at a specific current of 500 mA g(-1). The high rate capability is attributed to porous nature of the composite sample.

Tailored electrical conductivity, electromagnetic shielding and thermal transport in polymeric blends with graphene sheets decorated with nickel nanoparticles

Electromagnetic interference shielding (EMI) materials were designed using PC (polycarbonate)/SAN poly(styrene-co-acrylonitrile)] blends containing few-layered graphene nanosheets decorated with nickel nanoparticles (G-Ni). The graphene nanosheets were decorated with nickel nanoparticles via the uniform nucleation of the metal salt precursor on graphene sheets as the substrate. In order to localize the nanoparticles in the PC phase of the PC/SAN blends, a two-step mixing protocol was adopted. In the first step, graphene sheets were mixed with PC in solution and casted into a film, followed by dilution of these PC master batch films with SAN in the subsequent melt extrusion step. The dynamic mechanical properties, ac electrical conductivity, EMI shielding effectiveness and thermal conductivity of the composites were evaluated. The G-Ni nanoparticles significantly improved the electrical and thermal conductivity in the blends. In addition, a total shielding effectiveness (SET) of -29.4 dB at 18 GHz was achieved with G-Ni nanoparticles. Moreover, the blends with G-Ni exhibited an impressive 276% higher thermal conductivity and 29.2% higher elastic modulus with respect to the neat blends.

Structure and Dynamics of Octamethylcyclotetrasiloxane Confined between Mica Surfaces

Using a molecular model for octamethylcydotetrasiloxane (OMCTS), molecular dynamics simulations are carried out to probe the phase state of OMCTS confined between two mica surfaces in equilibrium With a reservoir. Molecular dynamics simulations are carried out for elevations ranging from 5 to 35 K above the melting point for the OMCTS model used in this study. The Helmholtz free energy is, computed for a specific confinement using the :two-phase thermodynamic (2PT) method. Analysis of the in-plane pair correlation functions did not reveal signatures of freezing even under an extreme confinement of two layers. OMCTS is found to orient with a wide distribution of orientations with respect to the mica surface, with a distinct preference for the surface parallel configuration in the contact layers. The self-intermediate scattering function is found to decay with increasing relaxation times as the surface separation is decreased, and the two-step relaxation in the scattering function, a signature of glassy dynamics, distinctly evolves as the temperature is lowered. However, even at 5 K above the melting point, we did not observe a freezing transition and the self-intermediate scattering functions relax within 200 ps for the seven-layered confined system. The self diffusivity and relaxation times obtained from the Kohlrausch-Williams-Watts stretched exponential fits to the late alpha-relaxation exhibit power law scalings with the packing fraction as predicted by mode coupling theory. A distinct discontinuity in the Helmholtz free energy, potential energy, and a sharp change in the local bond order parameter, Q(4), was observed at 230 K for a five-layered system upon cooling, indicative of a first-order transition. A freezing point depression of about 30 K was observed for this five-layered confined system, and at the lower temperatures, contact layers were found to be disordered with long-range order present only in the inner layers. These dynamical signatures indicate that confined OMCTS undergoes a slowdown akin to a fluid approaching a glass transition upon increasing confinement, and freezing under confinement would require substantial subcooling below the bulk melting point of OMCTS.

A Numerical Study of Indentation Using Indenters of Different Geometry

Finite element simulation of the Berkovich, Vickers, Knoop, and cone indenters was carried out for the indentation of elastic-plastic material. To fix the semiapex angle of the cone, several rules of equivalence were used and examined. Despite the asymmetry and differences in the stress and strain fields, it was established that for the Berkovich and Vickers indenters, the load-displacement relation can closely be simulated by a single cone indenter having a semiapex angle equal to 70.3degrees in accordance with the rule of the volume equivalence. On the other hand, none of the rules is applicable to the Knoop indenter owing to its great asymmetry. The finite element method developed here is also applicable to layered or gradient materials with slight modifications.

Elastic Waves in a Hybrid Multilayered Piezoelectric Plate

An analytical-numerical method is presented for analyzing dispersion and characteristic surface of waves in a hybrid multilayered piezoelectric plate. In this method, the multilayered piezoelectric plate is divided into a number of layered elements with three-nodal-lines in the wall thickness, the coupling between the elastic field and the electric field is considered in each element. The associated frequency dispersion equation is developed and the phase velocity and slowness, as well as the group velocity and slowness are established in terms of the Rayleigh quotient. Six characteristic wave surfaces are introduced to visualize the effects of anisotropy and piezoelectricity on wave propagation. Examples provide a full understanding for the complex phenomena of elastic waves in hybrid multilayered piezoelectric media.

水位变化引起分层边坡滑坡的实验研究

通过对分层的边坡在水位变化时滑坡的模拟实验,考察了分层坡体的滑坡模式、坡体变形、破坏和渗流引起的滑坡,重点考察了水位涨落速度对坡体稳定的影响,以及坡面从产生张拉裂缝直到形成滑面的整个过程,并对这类滑坡中的现象给出了定性解释.最后用有限元对实验坡体进行了应力和位移的静力场分析,计算结果与实验结果基本一致.

Graphite intercalation compounds under pressure

Motivated by recent experimental work, we use first-principles density functional theory methods to conduct an extensive search for low enthalpy structures of C$_6$Ca under pressure. As well as a range of buckled structures, which are energetically competitive over an intermediate range of pressures, we show that the high pressure system ($\gtrsim 18$ GPa) is unstable towards the formation of a novel class of layered structures, with the most stable compound involving carbon sheets containing five- and eight-membered rings. As well as discussing the energetics of the different classes of low enthalpy structures, we comment on the electronic structure of the high pressure compound and its implications for superconductivity.

Transparent electrode with a nanostructured coating.

Using single-walled nanotubes as an example, we fabricated transparent conductive coatings and demonstrated a new technique of centrifuge coating as a potential low-waste, solution-based batch process for the fabrication of nanostructured coatings. A theoretical model is developed to account for the sheet resistance exhibited by layered random-network coatings such as nanofilaments and graphene. The model equation is analytical and compact, and allows the correlation of very different scaling regimes reported in the literature to the underlying coating microstructure. Finally, we also show a refined experimental setup to systematically measure the curvature-dependent sheet resistance.

Mg-Al-NO_3层状双金属氢氧化物电性质研究

采用电泳法和电势滴定法测定出不同电解质(LiCl,NaCl和KCl）溶液中Mg-Al-NO_3层状双金属氢氧化物（Mg-Al-NO_3LDH)颗粒的$\Xi$电位、等电点、永久电荷密度以及零电荷点等电化学物理量，探讨了电解质、pH和样品化学组成对Mg-Al-NO_3LDH电性质的影响。研究发现一价阳离子Li+，Na+,K+对Mg-Al-NO_3LDH颗粒的等电点有影响，使等电点依次降低；由于永久电荷的存在，等电点与零电荷点不一致。随着样品中Al含量的增加，永久电荷密度依次增加，零电荷点依次增大，而等电点依次降低。

Effect Of A Negative Poisson Ratio In The Tension Of Ceramics

The effect of a negative Poisson ratio is experimentally revealed in the tension deformation of a natural layered ceramic. This effect can increase the volume strain energy per unit volume by 1100% and, simultaneously, decrease the deformation strain energy per unit volume by about 44%, so that it effectively enhances the deformation capacity by about 1 order of magnitude in the tension of the material. The present study also shows that the physical mechanisms producing the effect are attributed to the climbing on one another of the nanostructures in the natural material, which provides a guide to the design of synthetic toughening composites.