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  • 1
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The application limit of the MULTX program for predicting Renninger-scanning X-ray multiple diffraction data is extended in order to simulate Renninger scans for semiconductor single-crystal and heteroepitaxial structures recorded using synchrotron radiation. The experimental synchrotron-radiation Renninger scan for InP(006) bulk material is taken as the standard to analyse the effects of both the polarization factor and diffracted-beam path length. The polarization of the synchrotron-radiation beam is considered using a matrix approach. The diffracted-beam path length involved in the surface secondary beam cases is analysed taking into account the dynamical theory for perfect crystals and the kinematical theory as the limit of the dynamical case for thin crystals. Renninger scans of AlGaInAs quaternary layer structures, simulated with the MULTX program, show a very good agreement (R = 0.085) with the corresponding experimental data.
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 446-456 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: In this work, a method that takes advantage of the three-dimensional nature of the X-ray multiple-diffraction (MD) phenomenon for evaluating the crystalline perfection of semiconductors is proposed. The energy-transfer process among the MD beams can occur in a kinematical (secondary extinction) or a dynamical (primary extinction) regime. The effects that each regime can have on MD Bragg condition are theoretically investigated. The method provides information on size and misorientation of perfect-crystal regions as well as on the probability of interaction between them. The perfection of GaAs and Ge (001) surfaces after mechanical and/or chemical polishing has been investigated with this method and, as an extension of its applicability, porous silicon and GaAs (001) with Se ions implanted were also investigated.
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, we present evidence that Be3P2 microcrystals are formed in Be-doped phosphorus-based semiconductor compounds grown by chemical beam epitaxy. Our results suggest that microcrystal formation occurs when high Be concentrations (〉1018 cm−3) and temperatures higher than 500 °C are used for crystal growth. The main consequence of Be3P2 formation is a high phosphorus consumption close to these microcrystals that causes a large density of P vacancies in the semiconductor layer. This results in reduced electrical mobility, lattice parameter reduction, and poor crystalinity of the film in general. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4218-4226 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method of characterizing heteroepitaxial structures using hybrid multiple diffractions (hybrid MD) which appear in the layer Renninger scans (RS) together with the normal MD features, is reported. The three beam surface MD cases are used to provide high intensity and structural sensitivity. The RS peak measurements around the symmetry mirrors allow for the layer parallel lattice parameter determination. A simulation program was developed in order to account for the influence of the wavelength, incident beam divergence, sample mosaic spread, and substrate/layer lattice misorientation in the correct position and profile of the RS peaks. GaAs/Si samples with different layer thicknesses have been analyzed as an application of the method.
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  • 5
    ISSN: 1439-0264
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: By computed tomography the liver has an intermediate degree of attenuation, with a CT value (HU) between 70 and 75. However, this number may vary according to the generation of the apparatus, the use of contrasts medium, the efficiency of the detector, etc. The purpose of the present work was to evaluate the liver of the dog and related structures by means of a six-generation spiral CT scanner (Toshiba Ex Vision [[Au: please provide manufacturers details for ‘Toshiba Ex Vision’: city, state code (if USA) and Country]]), and the previous injection of intravenous contrast medium via cephalic vein. Four half-breed mature dogs (4–6 years, 15–20 kg) were used, two males and two females. The dogs were anaesthetized and kept over a stretcher in sternal recumbency. To evaluate the liver two different CT windows with different window width and window level were applied: soft tissue window (WW 652; WL -34) and mediastinal-vascular window (WW 352; WL 220). The CT images obtained allowed an excellent resolution at the level of the hepatic lobules, the gall bladder, the porta vein, the hepatic artery, the caudal cava vein, etc. The attenuation shades of these structures were very similar in the two used windows, however a better contrast was obtained with the soft tissue window.
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  • 6
    ISSN: 1439-0264
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Computed tomography (CT) is a modern technique of image diagnosis particularly recommended in human medicine to evaluate the existence of pulmonary pathological changes such as neoplasms, metastasis, interstitial infiltrates, etc. In veterinary medicine, however, few anatomical and clinical CT studies in the dog have used apparatus of the latest generation, including injection of intravenous contrast and application of regional specific CT windows with different window width (WW) and window level (WL) to evaluate the lungs, the pulmonary vessels and the bronchial structures. This methodology allows the obtaining of clear CT images with high capacity of tissue discrimination and different shades of attenuation. In this work we have planned a tomographic study of the lungs of the dog by using a six-generation spiral CT scanner (Toshiba Ex Vision), belonging to the private Medical Institute of Radiology ‘Irion’ of Porto Alegre, Brazil. Four mixed-breed mature dogs (4–6 years, 15–20 kg) were used, two males and two females. The dogs were anaesthetized and kept in a maximum inspiration when obtaining the images. Dogs were placed in a stretcher in a ventral or sternal recumbency. Previously, the contrast urografin® was injected in the cephalic vein. Different CT windows were applied in order to increase the quality of the images: pulmonary window (WW 928; WL -680), high-resolution pulmonary window (WW 1085; WL -750), and soft tissue window (WW 652; WL -34). The use of intravenous contrast, different CT windows and a modern CT apparatus produced excellent images of the pulmonary parenchyma, the pleural cavity, the pulmonary veins, the lobular rami of the pulmonary artery and the lobular bronchi.
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  • 7
    ISSN: 1439-0264
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The anatomical and clinical studies of computed tomography (CT) in the dog are still scarce. Particularly, there are few CT studies combining the use of rapid apparatus of the latest generation, the supply of contrast medium (digestive or intravenous) and the application of regional specific CT windows with different window width (WW) and window level (WL). The use of this CT methodology is particularly recommended in the evaluation of mediastinal masses, heart pathologies, etc. In this work the mediastinum of the dog was studied by using a sixth generation spiral CT scanner (Toshiba Ex Vision), belonging to the private Medical Institute of Radiology ‘Irion’ of Porto Alegre, Brazil. Four mixed-breed mature dogs (4–6 years, 15–20 kg) were used, two males and two females. The dogs were anaesthetized and kept at a maximum inspiration when getting the images. Previously, the urografin® contrast had been injected by peroral and intravenous (cephalic vein) via. Dogs were placed in a stretcher in sternal recumbency. Different CT windows were applied in order to increase the quality of the images and to obtain detailed attenuation shades of the mediastinum organs: soft tissue window (WW 652; WL -34), pulmonary window (WW 928; WL -680) and mediastinal-vascular window (WW 352; WL 220). The mediastinal space was studied craniocaudally from the level of the cranial cava vein, brachiocephalic trunk and left subclavian artery, to the caudal end of the lumbodiaphragmatic recess. The obtained images allowed a very good tomographic evidence of the great vessels, the heart, the thoracic portion of the trachea, the principal bronchi, the thoracic portion of the oesophagus, etc.
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  • 8
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 16 (1983), S. 360-360 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 9
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 366-371 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: In this work, X-ray Renninger scans for semiconductor single-crystal and heteroepitaxic structures are simulated. The simulation program is based on the iterative method for the calculation of multiple diffraction in imperfect crystals. The calculated diffracted-beam path length takes into account the small thickness of the heteroepitaxic layers in order to reproduce the survival of only surface secondary reflections in the layer Renninger scans. Applications of these simulations for bulk material (GaAs, GaSb), binary layers (GaAs/Si) and ternary layers (InGaAs/GaAs) show very good agreement with the corresponding experimental scans.
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  • 10
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution synchrotron radiation Renninger scans (RS) have been used in the analysis of hybrid reflections in the InGaP/GaAs structure. Four-beam cases involving two Bragg (primary and secondary) and one Laue (secondary) reflections of the 002 Renninger scans for the GaAs substrate and the InGaP layer were analysed in detail. Different structures of asymmetry regarding the in-plane directions [110] and [1{\bar 1}0] were observed from the measurements of the same three families of four-beam cases, {1{\bar 1}}{\bar 1}/{1{\bar 1}}3, {20}0/{20}2 and {3{\bar 1}}{\bar 1}/{3{\bar 1}}3, at several φ positions. The comparison between the experimental and MULTX simulated scan clearly shows a marked asymmetry observed on the {20}0/{20}2 contributions. An asymmetric peak instead of the simulated dip appears due to the layer Laue secondary beam {20}0 crossing the layer/substrate interface to generate a hybrid peak. The break in the lattice coherence for this heterostructure is shown by the occurrence of an unexpected dip in the layer RS, which does not obey the mirror symmetry.
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