Energy-band structure of CdTe and Si: a sp(s)k.p model

The energy bands of the direct-band-gap semiconductor (CdTe) as well as the indirect-band-gap semiconductor (Si), throughout the entire Brillouin zone, have been obtained by diagonalizing a 24×24 k.p Hamiltonian referred to basis states at We extend the sp³s^∗ basis functions by the inclusion of orbitals. We find that the sp³‘d’(s^∗)²k.p model is fairly sufficient to describe the electronic structure of these systems over a wide energy range, obviating the use of any d orbitals. Finally, the comparison with available theoretical results shows that the present model reproduces known results for bulk CdTe and Si, that is, their band structure, including s and p valence bands and the lowest two conduction bands.     

An explicit derivation of a relation between magnetization M and saturation magnetization Ms

An explicit relationship between a magnetization vector M and its saturation magnetization M_s is derived using the definition of M along with assumptions of the continuum exchange theory. The obtained expression is found to be an extension of the commonly used fixed-length constraint and represents the continuous analog of it for the elementary moment per unit volume. The derivation of this relation is carried out in detail and important potential implications relating to equations for M are also highlighted.     

Dipole solutions in theSU(2) andSU(3) gauge theory with electric and magnetic sources

The magnetic dipole solutions of Sikivie and Weiss are considered with the addition of a magnetic source and the validity of the observation that for large source strengths the energy of such solutions is lower than the energy of corresponding Coulomb solutions is examined. It is found that the presence of electric and magnetic sources leads to dipole solutions and that the introduction of a magnetic source does not alter the relationship between their energy and the energy of corresponding Coulomb solutions.     

Structural and magnetic changes in hydrogenated TiFe1−xNix alloys

A series of crystalline B2 and amorphous TiFe_1−xNi_x samples with different compositions and hydrogen loading ratios was characterized by XRD, VSM, TG, mass-spectrometry, and ¹H NMR in order to investigate possible correlations between the sample magnetization and hydrogen content. In crystalline samples, a reversible second-order phase transition from α-phase (B2 with soluble hydrogen) through a mixture of α- and ß-phase (B19 TiFe_1−xNi_xH_y) into a pure ß-phase was found. An increase of magnetization upon hydrogen loading was observed, depending on the concentration of iron in the samples. No unambiguous correlation between the hydrogen content and the saturation magnetization was found. The saturation magnetization of as-prepared amorphous samples was found to be significantly higher than in as-prepared crystalline ones. For both types of samples, magnetization remained high after dehydrogenation as well. Thermal desorption mass-spectra was found to strongly depend on composition, whereas structure, charging pressure, and H-content did not have tremendous effect. By ¹H NMR, enhanced relaxation due to strong magnetic moments was observed; however, by TEM the existence of Fe-clusters in hydrogenated samples could not be verified.     

Preparation, characterization and ionic conductivity studies of ZrO2 dispersed mixed halide matrix (KCl)0.9-(NaCl)0.1

Composite electrolytes in the system [(KCl)_0.9:(NaCl)_0.1]_1−y:(ZrO₂)_y were prepared and their ionic conductivities were studied. In our previous study on the mixed halide system (KCl)_1−x:(NaCl)_x, maximum conductivity (∼50 times that of the base KCl matrix) was found when x=0.1. The matrix (KCl)_0.9:(NaCl)_0.1 was dispersed with different concentration of ZrO₂ (powder) for the preparation of composites and their conductivities were determined. The maximum conductivity was developed for the composite having composition y=0.5. The matrices were prepared by melt-quench technique and the dispersion of ZrO₂ was carried out in liquid medium. The conductivity measurements of the composites were carried out by impedance spectroscopy technique. The composite [(KCl)_0.9:(NaCl)_0.1]_0.5:(ZrO₂)_0.5 was characterized by X-ray diffraction (XRD) analysis, differential thermal analysis (DTA), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). The conductivity of the composite [(KCl)_0.9:(NaCl)_0.1]_0.5:(ZrO₂)_0.5 as a function of temperature was also studied. The conductivity increase in the composite could be attributed to enhancement of defect concentration in the space charge region created at the interface between the host halide and the dispersoid.     

On the energy distribution profile of interface states obtained by taking into account of series resistance in Al/TiO2/p-Si (MIS) structures

The energy distribution profile of the interface states (N_ss) of Al/TiO₂/p-Si (MIS) structures prepared using the sol-gel method was obtained from the forward bias current-voltage (I-V) characteristics by taking into account both the bias dependence of the effective barrier height (?_e) and series resistance (R_s) at room temperature. The main electrical parameters of the MIS structure such as ideality factor (n), zero-bias barrier height (?_b0) and average series resistance values were found to be 1.69, 0.519 eV and 659 Ω, respectively. This high value of n was attributed to the presence of an interfacial insulator layer at the Al/p-Si interface and the density of interface states (N_ss) localized at the Si/TiO₂ interface. The values of N_ss localized at the Si/TiO₂ interface were found with and without the R_s at 0.25-E_v in the range between 8.4×10¹³ and 4.9×10¹³ eV⁻¹ cm⁻². In addition, the frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the structures have been investigated by taking into account the effect of N_ss and R_s at room temperature. It can be found out that the measured C and G/ω are strongly dependent on bias voltage and frequency.     

Thin films of asymmetrically substituted “ABAB-Type” indium phthalocyanine chloride: Preparation, structural characterization and optical properties

A synthetic route to the asymmetric octasubstituted metal-free phthalocyanines H₂Pcs (3-8) has been developed. They contain a combination of 2(3),16(17)-Tetra(2-ethyl-1-hexyl) and 9(10),23(24)-tetra(n-hexyl) as substituent groups in the peripheral positions. Thin films of the target asymmetric substituted “ABAB-Type” indium phthalocyanine chloride complex InPcCl 9, have been also fabricated for the first time, with different thickness (105-350 nm) using thermal evaporation technique. The structural and optical properties of the films have been investigated. The material in powder form showed a polycrystalline nature with triclinic structure. Miller indices, hkl, values for each diffraction line in X-ray diffraction (XRD) spectrum were calculated. The as-deposited films exhibited also a crystalline nature with a preferred orientation of growth. The scanning electron microscope showed the nano-structure property of the deposited films. The optical properties of the films are studied by the spectrophotometric measurements of the transmittance, T and the reflectance, R determined at the normal incident of the light in the spectral range 200-2500 nm. The refractive and absorption indices of the films are calculated and are found to be independent of film thickness of 105-350 nm. Different dispersion and absorption parameters are determined for the films.     

Effect of W co-doping on the optical,magnetic and electrical properties of Fe-doped BaSnO3

The effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO₃ has been studied. Polycrystalline BaSnO₃, BaSn_0.96Fe_0.04O₃ and BaSn_0.95Fe_0.04W_0.01O₃ samples were prepared using solid state reaction. In the analysis of powder X-ray diffraction patterns, the samples were found to be free of secondary phases. Diffuse reflectance spectra evidenced the substitution of Fe and W for Sn in the host BaSnO₃. Micro-Raman spectra confirmed the existence of oxygen vacancies in the samples. Upon W-1% co-doping, the ferromagnetic character of Fe-4% doped BaSnO₃ is suppressed drastically and its Curie temperature is reduced to 310 K from 462 K. The existence of F-centers and ferromagnetic interactions at room temperature is evidenced by the electron paramagnetic resonance and ferromagnetic resonance signals observed in the electron spin resonance spectra of the undoped and Fe-4% doped, (Fe-4% and W-1%) co-doped BaSnO₃ samples respectively. Suppression of ferromagnetism upon W co-doping is due to the fact that each W⁶⁺ ion donates two electrons to the host lattice and it reduces the number of oxygen vacancies that are essential for ferromagnetism to exist in the Fe-doped BaSnO₃ samples.     

Growth and characterization of organic nonlinear optical crystal: l-Valinium salicylate (LVS)

The new organic NLO crystal l-valinium salicylate (LVS) was grown by slow evaporation method using the mixed solvent of methanol and water in equal ratio. The crystal structure parameters were observed by powder and single crystal X-ray diffraction (XRD). The various functional groups present in the grown crystal were confirmed by Fourier transform infrared spectroscopy (FTIR) technique. ¹H and ¹³C Fourier transform nuclear magnetic resonance (FT-NMR) spectra were recorded to elucidate the molecular structure. The optical absorption study confirmed the good transmission window of the title crystal suitable for optical applications. The second harmonic generation (SHG) efficiency of LVS was confirmed by Kurtz Perry technique.     

Matrix assisted pulsed laser evaporation of poly(d,l-lactide) thin films for controlled-release drug systems

We report the successful deposition of the porous polymer poly(d,l-lactide) by matrix assisted pulsed laser evaporation (MAPLE) using a KrF* excimer laser (248 nm, τ = 7 ns) operated at 2 Hz repetition rate. The chemical structure of the starting materials was preserved in the resulting thin films. Fluence played a key role in optimizing our depositions of the polymer. We demonstrated MAPLE was able to improve current approaches to grow high quality thin films of poly(d,l-lactide), including a porosity control highly required in targeted drug delivery.     

Structural and magnetic properties of pyrochlores Gd2−xMxRu2O7 (M=Ho,Y)

In this paper we investigated the structural and magnetic properties of the Gd_2−xM_xRu₂O₇ (M=Ho and Y, x  =0.0, 0.1, 0.2, 1.0 and 2.0) pyrochlores. The samples were prepared by solid state reaction method, characterized structurally by X-ray diffraction with Rietveld refinement and magnetically by measuring the temperature dependence of the magnetization. X-ray diffractograms of all samples studied presented a cubic pyrochlore type crystal structure with lattice parameters varying linearly in accordance with Vegards law. It is shown that by substituting Gd by Ho one can tune the magnetic order of this system moving from antiferromagnetic (in the absence of Ho) to ferromagnetic (in the absence of Gd). On the other hand by replacing Gd for Y the antiferromagnetic order is decreased.©$\copyright$ 2010 Elsevier Science. All rights reserved     

Off-shell Bethe ansatz equation for osp(21) Gaudin magnets

The semi-classical limit of the algebraic Bethe ansatz method is used to solve the theory of Gaudin models. Via off-shell Bethe ansatz method we find the spectra and eigenvectors of the N−1 independents Gaudin Hamiltonians with symmetry osp(21). We also show how the off-shell Gaudin equation solves the trigonometric Knizhnik–Zamolodchikov equation.     

Results of an exact 2 scale transformation for two-dimensional lattice systems with O(2) and O(3) symmetry

The diagonal-to-diagonal transfer operator is considered on two-dimensional square lattices. A variational solution treating every second spin in an exact way is shown to yield very encouraging correlation length estimates for T>T_c in the cases of the XY and Heisenberg spin models.