Home  About us  Contact
 

Structural Quality (structural + quality)

Distribution by Scientific Domains
Physics and Astronomy75%

Kinds of Structural Quality

  • high structural quality
    		•

    Selected Abstracts

    Growth and characterization of near stoichiometric LiNbO3 single crystal

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007
    S. H. Yao
    Abstract A near stoichiometric LiNbO3 single crystal has been grown by the Czochralski method from a 58.5% Li melt hold in a large platinum crucible. High resolution X-ray rocking curves of 300 and 0006 reflections indicated that the near stoichiometric LiNbO3 crystal possesses the high structural quality. Compared with the congruent LiNbO3, the near stoichiometric LiNbO3 possesses shorter ultraviolet absorption edge, thus higher Li concentration. The OH, infrared absorption band analyses showed that the Li concentration in the near stoichiometric LiNbO3 crystal is higher than that in the congruent LiNbO3 crystal. This result is in good agreement with that of the ultraviolet absorption edge. The electro-optic (EO) coefficient ,22 of the near stoichiometric LiNbO3 crystal was measured to be 6.75 pm/V higher than that of congruent LiNbO3 crystal. It also proves the near stoichiometric LiNbO3 electro-optic Q-switched requires a low driving voltage and it is advantageous for the device performance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The impact of SiC substrate treatment on the heteroepitaxial growth of GaN by plasma assisted MBE

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005
    A. S. Brown
    Abstract We report on the impact of the preparation of the Si-face 4H-SiC(0001)Si substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001)Si are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    High-Conductivity Polymer Nanocomposites Obtained by Tailoring the Characteristics of Carbon Nanotube Fillers,

    ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008
    Nadia Grossiord
    Abstract We present a detailed study of the influence of carbon nanotube (CNT) characteristics on the electrical conductivity of polystyrene nanocomposites produced using a latex-based approach. We processed both industrially-produced multi-wall CNT (MWCNT) powders and MWCNTs from vertically-aligned films made in-house, and demonstrate that while the raw CNTs are individualized and dispersed comparably within the polymer matrix, the electrical conductivity of the final nanocomposites differs significantly due to the intrinsic characteristics of the CNTs. Owing to their longer length after dispersion, the percolation threshold observed using MWCNTs from vertically-aligned films is five times lower than the value for industrially-produced MWCNT powders. Further, owing to the high structural quality of the CNTs from vertically-aligned films, the resulting composite films exhibit electrical conductivity of 103,S m,1 at 2,wt% CNTs. On the contrary, composites made using the industrially-produced CNTs exhibit conductivity of only tens of S m,1. To our knowledge, the measured electrical conductivity for CNT/PS composites using CNTs from vertically-aligned films is by far the highest value yet reported for CNT/PS nanocomposites at this loading. [source]

    Investigation of ZnTe thin films grown by Pulsed Laser Deposition method

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007
    B. Kotlyarchuk
    Abstract This paper is devoted to optimization of the Pulsed Laser Deposition (PLD) growth condition of ZnTe films on various substrates and subsequent investigation of relevant parameters of growth process, structural, optical and electrical properties of grown films. Studies of the effect of growth parameters on the structural quality and properties of grown films were carried out. X-ray diffraction measurements showed that the ZnTe films, which have been deposited at optimal substrate temperatures, were characterized by a (111) preferred orientation with large average grain size. The optical transmission and reflectance in the energy range 1.5,5.5 eV for films grown at various substrate temperatures were measured. We calculated the variation in the absorption coefficient with the photon energy from the transmittance spectrum for samples grown at various substrate temperatures. Obtained data were analyzed and the value of the absorption coefficient, for allowed direct transitions, has been determined as a function of photon energy. We found that the undoped ZnTe films, which were grown by the PLD method, are typically p-type and possess resistivity in the range of 103 , cm at room temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Raman and transmission electron microscopy characterization of InN samples grown on GaN/Al2O3 by molecular beam epitaxy

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006
    J. Arvanitidis
    Abstract Raman spectroscopy and transmission electron microscopy were employed to study the vibrational properties and the microstructure of epitaxially grown InN films on GaN/Al2O3 templates. The variations of the InN lattice constants, as deduced by electron diffraction analysis, along with the red-shifted E22 mode frequency reveal that InN films exhibit residual tensile stress, strongly dependent on the epilayer growth temperature. Threading dislocations are the dominant structural defects in the films, having a density in the order of 109,1010 cm,2. Profile analysis of the E22 Raman peak by means of the Spatial Correlation Model provides useful information concerning the effective mean length for free phonon propagation (L), which is a measure of the structural quality of the samples. In all the studied samples, L monotonically increases with decreasing threading dislocation density of pure screw and mixed type character. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Optical studies on paramagnetic/superparamagnetic ZnO:Co films grown by magnetron sputtering

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010
    Limei Chen
    Abstract A series of Zn0.9Co0.1O thin films was grown by UHV-magnetron reactive sputtering at different Ar:O2 flow rates. Decreasing the oxygen flow rates towards oxygen deficient growth lowers the structural quality of the films. Furthermore, it alters the magnetic properties of the films measured by SQUID magnetometry. Paramagnetic behaviour was observed for samples of high structural quality grown under optimized conditions whereas superparamagnetism was observed for oxygen deficient samples due to the emergence of magnetic clustering. Optical spectroscopic methods such as Raman spectroscopy, transmission and photoluminescence reveal that the altered growth conditions even affect the optical spectra of the films, and indicate that the magnetic properties are strongly associated with the structural quality of the ZnO:Co films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Optical characterization of bulk GaN substrates with c -, a -, and m -plane surfaces

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    P. P. Paskov
    Abstract Thick free-standing GaN grown by hydride vapour phase epitaxy and epi-ready substrates with c -, a -, m -plane surfaces are examined by variable-temperature photoluminescence (PL), polarized PL and spatially resolved micro-PL. Both as-grown samples and polished substrates exhibit linewidth of the donor-bound exciton emission below 0.7 meV at 2 K indicative of a high structural quality of the material. For as-grown samples the relative intensity of green (2.4 eV) and red (1.8 eV) deep-level-defect emissions are found to decrease with increasing sample thickness. Based on plentiful two-electron-transition spectra measured in the samples the electronic fine structure of the donors and their bound-exciton complexes was examined and discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    GaN-based deep green light emitting diodes on silicon-on-insulator substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    S. Tripathy
    Abstract We have demonstrated deep green InGaN/GaN light emitting diodes (LEDs) on 100 nm thick (111)-oriented silicon-on-insulator (SOI) substrate. The LED structures are grown by metalorganic chemical vapour deposition. High-resolution X-ray diffraction and transmission electron microscopy have been used to characterize the structural quality of the LED layers. The room temperature electroluminescence (EL) spectrum from these LEDs is dominated by multiple interference peaks associated with the reflectivity changes at the bottom Si/SiO2 interfaces beneath AlN buffer. The spectral intensity of the LEDs in the deep green region is higher due to the larger substrate reflectance at longer wavelengths. A greater modulation in the spectral fringes in the longer wavelength regions is due to the presence of Fabry-Perot modes. Such InGaN/GaN light emitting structures on reflective SOI may be useful for the realization of phosphor-free white LEDs. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Realization of AlGaN/GaN HEMTs on 3C-SiC/Si(111) substrates

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
    Y. Cordier
    Abstract Cubic SiC/Si (111) template is an interesting alternative for growing GaN on silicon. As compared with silicon, this substrate allows reducing the stress in GaN films due to both lower lattice and thermal expansion coefficient mismatch, and can provide better heat dissipation. In this work, we first developed the epitaxial growth of 3C-SiC films on 50 mm Si(111) substrates using chemical vapor deposition. AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these films. Both the structural quality and the behavior of transistors realized on these structures show the feasibility of this approach. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Determination of the human type I interferon receptor binding site on human interferon-,2 by cross saturation and an NMR-based model of the complex

    PROTEIN SCIENCE, Issue 11 2006
    Sabine R. Quadt-Akabayov
    Abstract Type I interferons (IFNs) are a family of homologous helical cytokines that exhibit pleiotropic effects on a wide variety of cell types, including antiviral activity and antibacterial, antiprozoal, immunomodulatory, and cell growth regulatory functions. Consequently, IFNs are the human proteins most widely used in the treatment of several kinds of cancer, hepatitis C, and multiple sclerosis. All type I IFNs bind to a cell surface receptor consisting of two subunits, IFNAR1 and IFNAR2, associating upon binding of interferon. The structure of the extracellular domain of IFNAR2 (R2-EC) was solved recently. Here we study the complex and the binding interface of IFN,2 with R2-EC using multidimensional NMR techniques. NMR shows that IFN,2 does not undergo significant structural changes upon binding to its receptor, suggesting a lock-and-key mechanism for binding. Cross saturation experiments were used to determine the receptor binding site upon IFN,2. The NMR data and previously published mutagenesis data were used to derive a docking model of the complex with an RMSD of 1 Å, and its well-defined orientation between IFN,2 and R2-EC and the structural quality greatly improve upon previously suggested models. The relative ligand,receptor orientation is believed to be important for interferon signaling and possibly one of the parameters that distinguish the different IFN I subtypes. This structural information provides important insight into interferon signaling processes and may allow improvement in the development of therapeutically used IFNs and IFN-like molecules. [source]

    Gene therapy for cartilage defects

    THE JOURNAL OF GENE MEDICINE, Issue 12 2005
    Magali Cucchiarini
    Abstract Focal defects of articular cartilage are an unsolved problem in clinical orthopaedics. These lesions do not heal spontaneously and no treatment leads to complete and durable cartilage regeneration. Although the concept of gene therapy for cartilage damage appears elegant and straightforward, current research indicates that an adaptation of gene transfer techniques to the problem of a circumscribed cartilage defect is required in order to successfully implement this approach. In particular, the localised delivery into the defect of therapeutic gene constructs is desirable. Current strategies aim at inducing chondrogenic pathways in the repair tissue that fills such defects. These include the stimulation of chondrocyte proliferation, maturation, and matrix synthesis via direct or cell transplantation-mediated approaches. Among the most studied candidates, polypeptide growth factors have shown promise to enhance the structural quality of the repair tissue. A better understanding of the basic scientific aspects of cartilage defect repair, together with the identification of additional molecular targets and the development of improved gene-delivery techniques, may allow a clinical translation of gene therapy for cartilage defects. The first experimental steps provide reason for cautious optimism. Copyright © 2005 John Wiley & Sons, Ltd. [source]