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  • Articles  (152)
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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 182-184 (Feb. 1995), p. 255-258 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 600 (1990), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    BBA - Biochimica et Biophysica Acta 29 (1958), S. 444-445 
    ISSN: 0006-3002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Archives of Biochemistry and Biophysics 77 (1958), S. 236-238 
    ISSN: 0003-9861
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4368-4372 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have analyzed the thermal stability of ZnSe-based single quantum well structures grown on a GaAs substrate by applying a rapid thermal annealing process. The photoluminescence intensity of the quantum well was used as a monitor for the thermal changes induced by the annealing process. X-ray diffractometry yields information about the crystal quality and the strain condition before and after the thermal treatment. As a main result, we found that the thermal stability of the quantum well photoluminescence signal critically depends on the thickness of the II–VI buffer layer, i.e., the distance between the active layer and the GaAs-II–VI heterointerface. For a buffer layer thickness of about 38 nm, the quantum well signal is totally quenched after a 1 min annealing step at 500 °C, while clear luminescence signals can be observed in samples with a 1 μm buffer even for a 750 °C process. Additionally, by comparing CdZnSe/ZnSe and ZnSe/ZnSSe quantum wells, we found that the Cd–Zn interdiffusion seems to be more efficient than the S–Se interdiffusion. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 451-455 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated optical properties of ZnTe epilayers, Zn1−xMgxSeyTe1−y epilayers, and ZnTe/Zn1−xMgxSeyTe1−y quantum wells (QWs) grown on (100)-InAs substrates by molecular beam epitaxy. We observed several sharp photoluminescence lines close to the excitonic position and no detectable luminescence from deep levels in ZnTe epilayers. Bright luminescence has been obtained from Zn1−xMgxSeyTe1−y epilayers which are lattice matched with InAs. The band alignment of ZnTe/Zn1−xMgxTe QWs was found to be type I. The reduction of the band gap energy of the ZnTe layer due to a tensile strain was confirmed in this structure. Nearly lattice-matched ZnTe/Zn1−xMgxSeyTe1−y QWs have been fabricated. A type II band alignment was observed for many of these QWs. We estimated bowing parameters not only of the band gap but also of the valence band for ZnSeyTe1−y. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 112 (1993), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The scattering of acoustic waves in random media is investigated numerically by a finite difference method and is compared with the predictions of single scattering theory. the random media are characterized by autocorrelation functions which allow the construction of spatially anisotropic random structures with different correlation lengths a and b perpendicular and parallel to the propagation direction. If a equals b, the attenuation of the transmitted wave can be successfully explained by single scattering theory. the attenuation maximum occurs at kb≈ 1-2, where k is the wavenumber. For media with a 〉 b we observe a stronger attenuation than expected from single scattering theory for kb greater than 6. the attenuation peak is shifted to smaller kb values when the spatial anisotropy of the random fluctuations is increased. the investigation of the seismic coda shows that the single scattering theory cannot explain the time dependence of the coda. Coda Q, as determined from the coda decay rate under the single scattering assumption, does not describe the scattering attenuation. In 1-D random media the decay rate of the coda observed in transmission decreases with increasing standard deviation of the impedance fluctuations. In the 2-D case the decay rate increases slightly with the standard deviation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A ray-theoretical relation is established between the autocorrelation function of the slowness fluctuations of a random medium and the autocorrelation function of the traveltime fluctuations on a profile perpendicular to the general propagation direction of an originally plane wave. Although this relation can be inverted exactly, it is preferable for applications to use the results of a forward calculation for a modified exponential autocorrelation function which represents slowness fluctuations with zero mean. The essential parameters of this autocorrelation function, standard deviation ε and correlation distance a, follow by simple relations from the maximum and the zero crossing of the corresponding autocorrelation function of the traveltime fluctuations. The traveltime analysis of 2-D finite-difference seismograms shows that ε and a can be reconstructed successfully, if the wavelength-to-correlation-distance ratio is 0.5 or less. Otherwise, ε is underestimated and a overestimated; however, both effects can be compensated for.The average traveltime, as determined from the finite-difference seismograms, is slightly, but systematically shorter than the traveltime according to the average slowness, i.e. the wave prefers fast paths through the medium. This is in agreement with results of Wielandt (1987) for a spherical low-velocity inclusion in a full-space and with results of Soviet authors, summarized by Petersen (1990). The velocity shift is proportional to ε2, it has dispersion similar to the dispersion related to anelasticity, and it increases with the pathlength of the wave.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 102 (1990), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Energy flux models which have been proposed lately offer a unified concept of scattering attenuation and coda wave excitation. Here, an energy flux model for a plane wave propagating through a scattering layer above a homogeneous half-space is developed. It takes into account the intrinsic attenuation of the layer as well as diffusion of coda energy out of the layer into the half-space. All three parameters of the model—scattering attenuation, intrinsic attenuation and diffusion losses—can be determined from the coda strength relative to the direct arrival and the coda decay rate, if one makes some assumptions on the frequency dependence of intrinsic attenuation.The energy flux model has been tested with synthetic finite difference seismograms and has been found to give reliable results for both weak and strong scattering environments. It was then used for the analysis of short-period data from deep events recorded at the Warramunga seismic array in central Australia. an average scattering Q of about 640 at 1 Hz was found for the lithosphere beneath the array with a strong increase of Q with frequency above 1 Hz. Intrinsic Q is much higher than scattering Q and most of the coda decay is caused by diffusion of coda energy into the half-space below the scattering layer.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7051-7055 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Be-enhanced formation of CdSe quantum dots in CdSe/ZnSe heterostructures grown by migration enhanced epitaxy on (001)GaAs substrates has been investigated using photoluminescence spectroscopy, x-ray techniques (diffraction and reflectometry), and transmission electron microscopy. Coverage of the ZnSe starting surface with a fractional monolayer of beryllium selenide leads to enhanced island formation well below the CdSe thickness of 0.6 monolayer corresponding to the onset of the CdSe-rich island formation in the Be-free structures. The effect of the fractional Be coverage is demonstrated by observation of sharp lines in the photoluminescence signal from patterned mesas with dimensions down to 60 nm, which is due to the emission from individual exciton localization sites attributed to quantum dots. X-ray diffraction and reflectometry measurements on CdSe/ZnSe short-period superlattices with the submonolayer CdSe insertions confirm an enhanced roughening of the CdSe layer morphology in the case of beryllium coverage. Cross-sectional transmission electron microscopy on the SLs with BeSe fractional monolayer exhibits Cd-induced stress modulation along the CdSe sheets with a lateral scale of ∼4 nm, that can also be interpreted in favor of the BeSe-nucleated CdSe-based quantum dots. © 2000 American Institute of Physics.
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