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  • 1990-1994  (4)
  • 1993  (1)
  • 1992  (3)
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  • 1990-1994  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3820-3826 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thickness of the individual layers of molecular beam epitaxy grown pseudomorphic InyGa1−yAs (0.1≤y≤0.35)/GaAs/Al0.3Ga0.7As quantum well structures has been determined by transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) depth profiling, and reflection high energy electron diffraction (RHEED) with the aim of the compositional analysis of the ternary alloy films. Agreement between SIMS and TEM thickness data within 15% is found. Reliable RHEED data at y≥0.25, where the number of RHEED oscillations is drastically reduced by the three-dimensional growth of the InGaAs film, have been obtained by averaging repeated RHEED measurements. As compared with TEM, RHEED tends to lower values by 10% at maximum. The compositional data determined by the different methods including also photoluminescence (PL) agree within 20% in the technologically important region y≥0.2. At y=0.1, extreme accuracy requirements concerning the thickness determination limit the accuracy of SIMS and TEM to around 30%. Therefore PL and RHEED are superior at this concentration. An influence of the growth temperature on the In content at y=0.3 could be detected only by PL, demonstrating the excellent relative accuracy of PL.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2546-2548 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering by local vibrational modes of carbon-hydrogen pairs is reported for heavily carbon-doped epitaxial GaAs layers. Scattering by the longitudinal carbon mode of these pairs at 452 cm−1 shows a strong resonant enhancement for incident photon energies approaching the E1 band-gap energy of GaAs ((approximately-equal-to)3 eV). A possible mechanism for this resonance behavior is discussed in terms of the displacement of the carbon atom from its normal arsenic lattice site accompanied by a lengthening and weakening of the carbon-gallium bonds when carbon-hydrogen pairs form. The present findings demonstrate that resonant Raman scattering is an attractive tool for the detection of carbon-hydrogen pair formation in thin carbon-doped epitaxial GaAs layers grown from source materials containing hydrogen. The detection limit is estimated to be in the low 1018 cm−3 range.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cost of reproductive effort is known to result in a trade-off between current and future reproduction. Similarly, trade-offs in energy allocation may occur between components of reproductive effort, mating and parental effort, within a single reproductive episode. We investigated the energy allocated to mating effort (calling to attract females) and parental effort (donation of spermatophore nutrients at mating) by male bushcrickets, Requena verticalis, under two dietary regimes. Males provided with a low quality diet reduced the daily energy allocated to calling activity while maintaining their investment in spermatophores. Males provided with a high quality diet did not allocate more resources per day to their spermatophores but stored excess energy for future reproduction. Thus, on a per day basis, males appear to hold constant their investment in the spermatophore at the cost of reduced mating effort when resources are limited. Males on both diets, however, increased the size of their spermatophore donations when the interval between female encounters was increased. One explanation for this pattern could be a frequency-dependent optimization of spermatophore size.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 26 (1992), S. V 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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