Experimental analysis of true left-handed behaviour and transmission properties of composite metamaterials

We report the true left-handed transmission of a composite metamaterial (CMM) consisting of periodically stacked split-ring resonator (SRR) and wire elements. The negative permeability (μ < 0) gap is demonstrated explicitly by comparing SRR and closed-ring resonator structures. We confirm experimentally that the plasma cut-off frequency of the CMM is determined by the combined dielectric response of SRR and wire elements, and it is much lower than that of the wire-only medium. This is crucial to identify the left-handed transmission bands of the CMM. We further investigate the effect of intralayer and interlayer disorder on the transmission spectrum of CMM arising from misaligned fabrication and stacking of the SRR layers. We found that the intralayer disorder affects the μ < 0 gap of SRRs and the left-handed transmission band of CMM significantly, whereas the SRR transmission is rather immune to interlayer disorder.     

Room-temperature magnetoresistance in CoFeB/STO/CoFeB magnetic tunnel junctions

A series of Co₄₀Fe₄₀B₂₀/SrTiO₃/Co₄₀Fe₄₀B₂₀ magnetic tunnel junctions with a bottom-pinned synthetic antiferromagnet have been prepared by sputtering. Devices optimally annealed at 325 °C exhibit an exchange bias of about 65 mT, and a tunnel magnetoresistance of 2%. The smaller than predicted effect is attributed to the lack of epitaxy between the crystallized CoFeB electrodes and the SrTiO₃ (STO) barrier, due to poor crystal quality of the barrier layer. Unlike MgO, well-crystallized, oriented STO does not grow on amorphous Co₄₀Fe₄₀B₂₀.     

Spectroscopic,electrochemical, theoretical characterization and biological evaluation of a ferrocenyl-substituted unsymmetric azine ligand and its Cu(II) complex

Ferrocenyl-substituted unsymmetrical azine and its Cu(II) complex were prepared. The redox active ferrocene-based azine was obtained by condensation of 1-[(E)-hydrazono]-5-bromo-2-hydroxybenzene with ferrocene carboxaldehyde. The ferrocenyl ligand and its Cu(II) complex were characterized by IR, UV–vis, NMR, X-ray, magnetic susceptibility, molar electrical conductivity measurements, and TG techniques. The redox behaviors of the ferrocene compounds were investigated by cyclic voltammetry. Structural parameters and spectroscopic properties of the ligand and the Cu(II) complex were calculated by employing density functional theory (DFT) and time-dependent DFT and compared with available experimental data. We found slightly stronger binding ability for Cu(II) complex than the free ligand. DNA binding abilities for ferrocenyl-substituted unsymmetrical azine ligand and its Cu(II) complex are higher than some reported ferrocene compounds. We also studied DNA cleavage, superoxide and DPPH radical scavenging abilities of the compounds. Furthermore, the synthesized organometallic compounds can be bound to DNA through an intercalative mode.     

Synthesis and Optical Properties of Novel Red-Emitting PbNb<Subscript>2</Subscript>O<Subscript>6</Subscript>: Eu<Superscript>3+</Superscript> Phosphors

Undoped and PbNb₂O_6:Eu³⁺ (1.0 ≤ x ≤ 6.0 mol%) phosphors were synthesized at 1100 °C for 3.5 h by the conventional solid state reaction method. Synthesized PbNb₂O₆:Eu³⁺ phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed series of excitation peaks between 350 and 430 nm due to the 4f–4f transitions of Eu³⁺. For 395.0 nm excitation, emission spectra of Eu³⁺ doped samples were observed at 591 nm (orange) and 614 nm (red) due to the ⁵D₀ → ⁷F₁ transitions and ⁵D₀ → ⁷F₂ transitions, respectively. PL analysis results also showed that the emission intensity increased by increasing Eu³⁺ ion content. No concentration quenching effect was observed. The CIE chromaticity color coordinates (x,y) of the PbNb₂O₆:Eu³⁺ phosphors were found to be in the red region of the chromaticity diagram.     

Electroless synthesis of Ag nanoparticles on deposited nanostructured Si films

Two and three-dimensional Ag nanoparticle ensembles were synthesized on deposited nanostructured column-void Si films simply by film immersion into pure Ag(2)SO(4) or AgNO(3) solutions. In addition to functioning as a reducer, this nanostructured material provides immobilization and monodispersion of the Ag nanoparticles due to its systematic nanoscale topography. This is accomplished without the requirement of a surfactant, capping agent, or linker. Kinetics, as monitored from plasmon optical extinction, and infrared spectroscopy suggest accompanying oxide growth limits and finally inhibits synthesis enabling nanoparticle size control. Kinetics is also limited by Ag+ transport through the voids unless the Si film is ultrathin. Our synthesis approach offers significant advantages for surface-enhanced molecular detection, including the absence of any agents on the nanoparticle surfaces and the ability to obtain nanoparticle ensembles on any substrate.     

Nickel(II) complexes prepared from NNN type ligands and pseudohalogens

Six nickel(II) complexes, using azide and thiocyanate ions, have been synthesized from bis-2,6(pyrazol-1-yl)pyridine (pp) and some methyl derivatives, 2-(3,5-dimethyl(pyrazol-1-yl)-6-(pyrazol-1-yl)pyridine (app) and bis-2,6(3,5-dimethyl(pyrazol-1-yl) pyridine (dmpp) in non-aqueous media. The complex structures were analyzed using elemental analysis, IR spectroscopy and thermogravimetry. Appropriate crystals of complex, containing azide [Nipp(N₃)₂]·MeOH (I) and thiocyanate [Nidmpp(SCN)₂·MeOH] (VI) were prepared and the molecular structures determined using X-ray diffraction. Complex I was seen to be dinuclear as stated in literature, space group P2₁/n, monoclinic, a=10.503, b=10.681, c=13.291 Å, β=106.56° and Z=2 whereas complex VI was found to be mononuclear, space group P2₁/n, monoclinic, a=8.646, b=12.614, c=20.697 Å, β=97.18° and Z=2. The Ni(II) coordination in both complexes were octahedral. Thermogravimetric studies showed azide containing structures to resemble the characteristics of explosive materials. Coordinative MeOH were seen to leave the structure in thiocyanate containing complexes, followed by irregular degradation above 300°C.     

Structural and Near-Infrared Properties of Nd<Superscript>3+</Superscript> Activated Lu<Subscript>3</Subscript>NbO<Subscript>7</Subscript> Phosphor

Undoped and Nd³⁺ doped lutetium niobate phases have been prepared by a conventional solid state reaction method using lutetium acetate and niobium oxide at 1250 °C for 6 h. X-ray diffraction patterns of the 6 mol% Lu₃NbO₇ sample exhibited a cubic fluorite single phase. Phase structure exhibited interesting crystallization behaviour depending on increasing Nd³⁺ concentration which led to a Lu₃NbO₇ single phase formation during the heat treatment process. SEM investigations were also in agreement with the XRD results. Morphologies of Nd³⁺ doped lutetium niobate powders exhibited oval like shapes and grain sizes varied between 0.3 and 5 μm. Near-infrared luminescence properties of Nd³⁺ doped Lu₃NbO₇ were also studied. 1.06 μm laser transition characteristics of Nd³⁺ doped lutetium niobate have been observed. Concentration quenching phenomenon was not detected depending on increasing Nd³⁺ doping concentrations at room temperature.     

Numerical modeling of formability of extruded magnesium alloy tubes

In this paper, a constitutive framework based on a rate-dependent crystal plasticity theory is employed to simulate the large strain deformation phenomena in hexagonal closed-packed (HCP) metals such as magnesium. The new framework is incorporated into in-house codes. Simulations are performed using the new crystal plasticity model in which crystallographic slip and deformation twinning are the principal deformation mechanisms. Simulations of various stress states (uniaxial tension, uniaxial compression and the so-called ring hoop tension test) for the magnesium alloy AM30 are performed and the results are compared with experimental observations of specimens deformed at 200 °C. Numerical simulations of forming limit diagrams (FLDs) are also performed using the Marciniak–Kuczynski (M–K) approach. With this formulation, the effects of crystallographic slip and deformation twinning on the FLD can be assessed.     

Modelling the behaviour of polycrystalline austenitic steel with twinning-induced plasticity effect

A micromechanical model using the scale transition method in elastoviscoplasticity has been developed to describe the behaviour of those austenitic steels that display a TWIP effect. A physically based constitutive equation at the grain scale is proposed considering two inelastic strain modes: crystallographic slip and twinning. The typical organizations of microtwins observed in electron microscopy are considered, and the twin–slip as well as the twin–twin interactions are accounted for. The parameters for slip are first fitted on the uniaxial tensile response obtained at intermediate temperatures (when twinning is inhibited). Then, the parameters associated with twinning are identified using the stress–strain curve at room temperature. The simulated results in both macro and micro scales are in good agreement with experimentally obtained results.     

Multipole cross sections for collisional excitation of highly charged ions by isotropic electrons

The relativistic distorted-wave program of the flexible atomic code for calculating the cross sections for electron-impact excitation of ions between fine-structure levels is extended to get the multipole components of cross sections in the case of excitation by isotropic electrons. These components may be needed for interpreting the intensity and polarization of line emissions from thermal plasmas exposed to anisotropic radiations, such as the solar corona under photosphere irradiation. Illustrative numerical results are given for excitation of Si-like Fe¹²⁺ between the , and levels. These results can be useful in the analysis of infrared forbidden lines emitted from the solar corona. A comparison is made with the only published work based on the semi-relativistic distorted-wave approximation, showing some agreement for the excitation and discrepancies for the weak transition .