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  • Electronic Resource  (6)
  • 1990-1994  (6)
  • 1994  (2)
  • 1991  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Intersubband transitions in partially interdiffused GaAs/AlGaAs multiple quantum-well structures (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2195-2199 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Continuous tuning over the entire 8–12 μm wavelength range is demonstrated for the intersubband absorption resonance in n-doped GaAs/AlxGa1−xAs multiple quantum-well structures following partial interdiffusion of the well and barrier layers via rapid thermal annealing. The data indicate that redshifting of the intersubband absorption resonance arises both from interdiffusion-induced modification of the confining potential and from a decrease in the depolarization shift. The latter effect is due in part to a decrease in the free-carrier concentration within the Si-doped quantum wells following rapid thermal annealing. Significant diffusion of the localized Si dopant is also observed over the range of annealing temperatures investigated here. Calculated values of the Al-Ga interdiffusion coefficient, as a function of anneal temperature, indicate that Si diffusion through the heterointerfaces contributes substantially to layer intermixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350334
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative assessment of Be acceptors in GaAs by local vibrational mode spectroscopy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 971-974 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Be-doped epitaxial layers of GaAs grown by molecular beam epitaxy have been studied by local vibrational mode spectroscopy combining infrared absorption and Raman scattering. Calibration factors for both experimental techniques have been derived which enable quantitative assessments to be made of the concentrations of Be acceptors in GaAs. In Raman spectroscopy the detection limit is ≈ 3×1018 cm−3 for as-grown layers only 10 nm in thickness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347289
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of In on Si local vibrational modes in InxGa1−xAs (0≤x≤0.12) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7797-7804 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local vibrational modes (LVM) of Si in substitutional sites have been observed by resonant Raman spectroscopy in highly doped (≥8×1018 cm−3) InxGa1−xAs layers, either relaxed or under strain, on [100] GaAs substrates. The peak frequency ωLVM of the Si on Ga site (SiGa) LVM in unstrained samples shifts to lower values with increasing In content. For x≤0.10 this shift is clearly higher than expected from a linear interpolation between the measured values in the binaries. The comparison between the SiGa peak frequency measured in both a full strained layer and a relaxed layer with similar composition provides a rough determination of the deformation potentials for the SiGaLVM in these layers: q/ω2LVM=−2.7±1 and p/ω2LVM=−2.5±1. As the In content becomes higher the width of the SiGa peak increases much more than that of the GaAs-like longitudinal optical-phonon peak, revealing the splitting due to the loss of local symmetry introduced by the In. New calibration factors for the Si-defect concentrations have been deduced, which allow estimation of the solubility limit for the Si incorporation in substitutional positions, which ranges from 2.3×1019 to 2.6×1019 cm−3 for the layers at the growth conditions used. The analysis of the integrated intensity of the LVM Raman peaks indicates that the degree of electrical compensation is clearly reduced for increasing In up to x≤0.05, due to both an increase of the solubility limit for Si in these layers and a saturation or slight reduction of the SiAs-related defect concentrations. This conclusion is also supported by Hall and plasmon measurements. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358521
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  • 4
    Electronic Resource
    Electronic Resource
    Redistribution of epitaxial Si on (001) GaAs during overgrowth by GaAs (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2730-2732 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We examine the stability of pseudomorphic submonolayer Si films embedded in (001) GaAs by molecular-beam epitaxy. Secondary ion-mass spectrometry depth profiling reveals the presence of 1019 Si-atoms/cm3 in the first 40 nm of the GaAs cap layer. The systematic investigation of samples having different cap thickness by Hall effect measurements and local vibrational mode Raman spectroscopy allows us to identify the site distribution of Si atoms in the cap layer and yields insight into the migration mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105898
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  • 5
    Electronic Resource
    Electronic Resource
    Zeitstandverhalten einiger fortschrittlicher Schaufelwerkstoffe für IndustriegasturbinenAuszug aus einer beim Fachbereich Maschinenbau der Technischen Hochschule Darmstadt einzureichenden Dr.-Ing. Diss. von M. Maier (1994)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 25 (1994), S. 273-283 
    Details
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Creep rupture behaviour of some advanced materials for industrial gas turbinesThe creep rupture behaviour of three DS-alloys, an ODS-alloy and a PM-alloy for gas turbine blades is investigated up to 20 000 h test duration. Further, the elastoplastic behaviour is determined in tensile tests and the contraction behaviour in long-term annealing tests. On this basis, a characterisation of the strength and partly a modelling of the deformation behaviour of the alloys is given.
    Notes: Das Zeitstandverhalten von drei Ds-Werkstoffen, einem ODS-Werkstoff und einer PM-Legierung für Gasturbinenschaufeln wird in Versuchen bis zu 20 000 h Dauer ermittelt. Ferner wird das elasto-plastische Kurzzeitverhalten in Warmzugversuchen und das Kontraktionsverhalten in langzeitigen Glühversuchen bestimmt. Auf dieser Grundlage erfolgt eine Beschreibung des Festigkeits-und teilweise auch des Verformungsverhaltens der untersuchten Werkstoffe im Hochtemperaturbereich.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19940250704
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  • 6
    Electronic Resource
    Electronic Resource
    1H NMR and molecular mechanics studies of epimeric ethyl esters of 20(R, S)-hydroxy-23-norcholanoic acids (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 137-142 
    Details
    ISSN: 0749-1581
    Keywords: 20(R,S)-Hydroxy-23-norcholanoic acid derivatives ; 1H NMR ; Pyridine-induced shifts ; Molecular mechanics calculations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton chemical shifts for the C-18, C-21, —CO2CH2CH3 and —CO2CH2CH3 protons of epimeric ethyl esters of 20(R,S)-hydroxy-23-norcholanoic acids were measured in deuteriochloroform and pyridine-d5. The observed solvent shifts due to specific OH - pyridine hydrogen-bonded complexes allowed the quantification of the epimeric mixtures by analysis of the pyridine-d5 1H NMR spectra. The main features of the pyridine-induced shifts are rationalized in terms of the preferred conformations for the 20R- and 20S-epimers, which are predicted by molecular mechanics calculations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290208
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