O. Arteaga  Z. El‐Hachemi  A. Canillas 《physica status solidi (a)》2008,205(4):797-801

Transmission‐mode perpendicular incidence phase modulated ellipsometry was applied to study anisotropic thin films of porphyrin J‐aggregates. A customized data acquisition system and measurement method was implemented to measure seven Mueller matrix elements, which allow us to determine the circular birefringence and dichroism as well as the linear birefringence and dichroism of solid‐state films. The examples shown illustrate the performance of the method for obtaining the true circular dichroism and consequently for detecting structural differences in chiral aggregates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

S. A. Fayek  M. R. Balboul  M. El‐Ocker 《physica status solidi (a)》2007,204(4):1162-1170

The effects of adding transition metals (Ni and Co) on the optical and electrical properties of four thin films Ni_1.25Fe_1.5Ge_0.25O₄, Ni_1.5Fe₁Ge_0.5O₄, Co₁Fe₁Ge_0.5O₄ and Co_1.25Fe_1.5Ge_0.25O₄ are reported. X‐ray diffraction was used to ascertain the amorphization nature of the deposited films. The optical absorption behavior of these films was studied from the transmission and reflection in the range 200–1100 nm. It was found that the optical band gap increases on increasing GeO₂ and arises from direct forbidden transitions. The opposite trend was found with the band tail width of the localized state. Optical constant parameters such as refractive index and absorption index were obtained for the films. The results for the alternating‐current (ac) conductivity and the dielectric constant of the four films are presented over the temperature range 277–357 K and the frequency range 0.1 to 1000 kHz. The ac conductivity increases with temperature and frequency and decreases with the increase in Ni²⁺ or Co²⁺ content. The effect of composition and temperature on the dielectric constant was also studied. The frequency variation of the dielectric constant does not have a peak, unlike many semiconductor glasses. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

A. Ben Fredj  Y. Oussaifi  N. Bouarissa  M. Said 《physica status solidi b》2006,243(12):2780-2787

Using the empirical pseudopotential approach, we have investigated the electronic properties of GaN, ScN and their hypothetical alloys Sc_x Ga_1−x N in the zinc‐blende structure. The band gaps at Γ‐, X‐ and L‐points as well as the electron effective masses of Γ and X valleys were calculated as a function of scandium molar fraction x. The agreement between our results and the available experimental and previously calculated data is fair. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Kortunov P  Vasenkov S  Kärger J  Fé Elía M  Perez M  Stöcker M  Papadopoulos GK  Theodorou D  Drescher B  McElhiney G  Bernauer B  Krystl V  Kocirik M  Zikanova A  Jirglova H  Berger C  Gläser R  Weitkamp J  Hansen EW 《Magnetic resonance imaging》2005,23(2):233-237

Pulsed-field gradient nuclear magnetic resonance (PFG NMR) has been applied to study molecular diffusion in industrial fluid catalytic cracking (FCC) catalysts and in USY zeolite for a broad range of molecular displacements and temperatures. The results of this study have been used to elucidate the relevance of molecular transport on various displacements for the rate of molecular exchange between catalyst particles and their surroundings. It turned out that this rate, which may determine the overall rate and selectivity of FCC process, is primarily related to the diffusion mode associated with displacements larger than the size of zeolite crystals located in the particles but smaller than the size of the particles. This conclusion has been confirmed by comparative studies of the catalytic performance of different FCC catalysts.  相似文献   

    

F. El Haj Hassan 《physica status solidi b》2005,242(15):3129-3137

The first ab initio calculations were carried out for the electronic, structural and thermodynamic properties of BN_xSb_1–x, BP_xSb_1–x and BAs_xSb_1–x boron ternary alloys. The full potential linearized augmented plane wave (FP‐LAPW) method was employed within density functional theory (DFT). The local density approximation was used with generalized gradient correction (GGA) as well as the Engel–Vosko GGA formalism to calculate the band gap. The effect of composition on lattice constants, bulk modulus and band gap was investigated. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the three alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co‐workers. In addition, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔH_m as well as the phase diagram. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

M. El‐Muraikhi  M. E. Kassem  M. Gaafar  M. M. H. Abdel Gawad  I. M. Ragab 《physica status solidi (a)》2005,202(1):163-169

The dielectric spectroscopy of metal–metal sulfate LiRbSO₄ samples are described with particular emphasis on sensor performance to be used in the field of radiation. The obtained results as the effect of different electron energy beams at fixed dose, 0.5 Gy, showed abrupt change of the electrical properties (electrical conductivity, capacitance, and loss tangent). The results can be explained on the basis of radiation‐induced defects followed by radiation quenching. The prepared samples can be used in the field of radiation dosimeter.  相似文献   

    

A. Rebey  A. Bchetnia  B. El Jani 《physica status solidi (a)》2005,202(14):2759-2763

The electrical properties of vanadium‐doped GaAs grown by metalorganic vapor phase epitaxy were studied between 77 and 300 K. The temperature‐dependent electron concentration, for different partial pressures of VCl₄, was simulated using the charge balance equation. A calculation model was used with parameters (energy levels and V concentration) derived from photoluminescence, deep‐level transient spectroscopy and secondary ion mass spectroscopy measurements. The magnitude and the temperature dependence of neutral and ionized V concentrations were determined. It is shown that most of the V concentration is inactive. This is in good agreement with some previous reports in the literature. The detailed analysis including the probability of V donor incorporation in GaAs was then extended to explain the evolution of electron concentration as a function of partial pressure of VCl₄. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

H. Fitouri  Z. Benzarti  I. Halidou  T. Boufaden  B. El Jani 《physica status solidi (a)》2005,202(13):2467-2473

The SiN treatment of the sapphire substrate for GaN growth induces a spectacular effect on the in situ reflectometry monitoring signal. Different growth modes are observed. The evolution of the reflectometry signal is simulated by the scattering theory approximation. The point‐by‐point analysis reveals that the roughness (rms) increases in the first region where the growth mode is dominated by the formation of isolated and three‐dimensional hillocks. The rms attains a maximum value exceeding that authorized by the Rayleigh criteria. Another approach based on the effective medium approximation is used to simulate the entire reflectometry signal evolution. An effective refractive index and a growth rate profile are determined. The results obtained are in accordance with the observations done by the in situ ellipsometry monitoring. We have also studied the evolution of the defined recovery time as a function of the SiH₄ flow rate and the SiN duration. Based on the concept of a nano‐epitaxial mask, induced by the SiN treatment of the sapphire surface, we have proposed a schematic model of the GaN growth that explains the recovery‐time behavior. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

A. A. El‐Daly 《physica status solidi (a)》2004,201(9):2035-2041

In this study, tensile tests of Pb–9.5Sn–0.5wt%Sb bearing alloy were investigated with respect to the effect of testing temperatures ranging from 393 to 473 K and strain rates ranging from 9.1 × 10^–4 to 2 × 10^–2 s^–1. The tensile tests revealed that the solder alloy exhibits high ductility at 433 K and 5 × 10^–3 s^–1. Strain rate sensitivity parameter m and activation energy were determined to clarify the deformation mechanism. The effects of Sb‐addition on the tensile properties of Pb–9.5Sn–0.5wt%Sb solder alloy were studied by comparing the tensile deformation behaviour of the two solders Pb–10wt%Sn and Pb–10Sn–1.5wt%Zn. Microstructural analysis confirmed that the mechanism controlling the tensile behaviour is a grain boundary sliding (GBS). This study revealed that the Pb–9.5Sn–0.5wt%Sb alloy shows a good combination of high strength and greater ductility by grain refinement. Also, the difference in the morphology and distribution of second phase particles caused by the Sb‐addition resulted in better tensile properties. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Mustafa Kamal  Maher El‐Tonsy  Abu Bakr El‐Bediwi  Eman Kashita 《physica status solidi (a)》2004,201(9):2029-2034

Structure, internal friction, hardness, thermal, electrical and mechanical properties of the rapidly solidified Bi_55.5Pb_44.5 eutectic alloy have been investigated. X‐ray diffraction and optical metallographic analysis show that the Bi_55.5Pb_44.5 eutectic alloy consists of rhombohedral bismuth phase, face centered cubic lead phase, and a metastable [χ(Pb–Bi)] phase. The physical properties such as thermal, electrical and mechanical properties of the Bi_55.5Pb_44.5 eutectic alloy have been interpreted in terms of the different contributions from each structural parameter. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献