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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented on the long-term ((approximately-greater-than)8 yr) degradation of AlxGa1−xAs-AlAs -GaAs quantum well heterostructure material because of the instability of underlying (internal) AlAs layers. Material containing thicker (〉0.4 μm) AlAs "buried'' layers (confining layers) is found to be much less stable than material containing thinner ((approximately-less-than)200 A(ring)) AlAs layers. Hydrolysis of the AlAs layers because of cleaved edges and pinholes in the cap layers leads to the deterioration.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented showing limited layer disordering (or intermixing) of S-diffused Se-doped or C-doped AlxGa1−xAs-GaAs superlattices. The S diffusion is characterized via secondary-ion mass spectroscopy, shallow angle beveled cross sections, and absorption measurements. Limited intermixing of column-III-site atoms (Al(arrow-right-and-left)Ga) as well as minimal displacement of the column-V-site acceptor C is observed. The S diffusion depth is much greater than that of the layer disordering, the magnitude of which is similar to that of native-defect vacancy-assisted disordering (vacancy VIII).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented on a photopumped rectangular (w=40 μm, l=250 μm) quantum well heterostructure (QWH), with variable resonator Q along the sample, showing that phonon-assisted laser operation predominates. To achieve variable resonator Q, the QWH sample is heat sunk embedded in In over half of its length (reflecting edges, high Q), as opposed to simple contact with a Au shim over the remaining half and no reflecting metal on the sample edges (low Q). Photopumping at the low Q, high Q boundary near the sample center turns on and off the n=1 confined-particle recombination transition (E11 ) and sets a higher energy experimental (as well as calculated) reference, (h-dash-bar)ω2 =E11, for the lower energy phonon-assisted laser operation, (h-dash-bar)ω1 =E11 −(h-dash-bar)ωLO .
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented showing that photopumped AlxGa1−xAs-GaAs quantum well heterostructures (QWHs) are capable of stimulated emission (because of the large confined phonon population) one and two longitudinal optical (LO) phonons below the lowest confined-particle electron-to-heavy hole transition (e1→h1). The phonon-assisted laser operation two phonons below the e1→h1 transition (ΔE=2(h-dash-bar)ωLO=2×36 meV) is identified unambiguously using (on a single sample) two types of heat sink configurations, high Q to turn on and low Q to turn off the stimulated emission on the e1→h1 (reference) transition. Because the one- and the two-phonon laser operations (4.2 K) are spectrally very narrow, narrower than that on QW confined-particle transitions, their separation affords an accurate measurement of QW phonon energy ((h-dash-bar)ωLO=36.1 meV).
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2013-08-31
    Description: Hydrogen permeability, diffusivity, and solubility data were obtained for eight wrought and cast high temperature alloys over the range 650 to 815 C. Data were obtained for both uncoated alloys and wrought alloys coated with four commercially available coatings. Activation energies for permeability, diffusivity and solubility were calculated.
    Keywords: METALLIC MATERIALS
    Type: IITRE-M06004-36 , DOE/NASA/0006-1 , NAS 1.26:165209 , NASA-CR-165209
    Format: application/pdf
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented showing that the key to observing the phonon-assisted photopumped laser operation of narrow rectangular samples of AlxGa1−xAs-GaAs quantum well heterostructures (QWHs) is the control of the edge-to-edge resonator Q across the sample. If the sample is heat sunk in metal, with metal reflectors folded upward along the edges, the resonator Q across the sample is high, and laser operation across the sample on confined-particle states (a reference) and along the sample a phonon lower in energy (ΔE≈(h-dash-bar)ωLO) is observed. If the sample edges across the sample are left uncoated (weakly reflecting, low Q), laser operation is observed only along the sample (longitudinal modes) but shifted (ΔE≈(h-dash-bar)ωLO) below the confined-particle states and absorption. A QWH rectangle, with proper heat sinking and control of its edge-to-edge resonator Q, can act as a hot-phonon "spectrometer'' if it is fully photopumped across its width and is only partially pumped along its length.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Impurity-induced layer disordering experiments on AlxGa1−xAs-GaAs quantum well heterostructures (QWHs) that are doped heavily with carbon are described. The data show that carbon doping retards Al-Ga interdiffusion relative to an undoped crystal, and that interdiffusion in C-doped QWHs is not enhanced by a Ga-rich (versus As-rich) annealing ambient. The data are inconsistent with most Fermi-level-effect models for layer disordering that do not include chemical impurity dependence or sublattice dependence, and that do not consider the possibility of inhibited Al-Ga interdiffusion in extrinsic crystals.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2019-07-18
    Description: Hydrogen has the potential of increased use in the future as an environmentally friendly fuel. It has, however, shown a tendency to embrittle some materials. To be used in a safe manner and to exploit its full potential, it will be necessary to develop a database of material properties in hydrogen environment. The tests needed to produce this data are costly to perform (tensile test cost 25 times more and low cycle fatigue test are 55 times as expensive). Moreover, there is presently a lack of universal test methods to ensure standardized data within the hydrogen community. Each of the industries that work with hydrogen (aerospace, petroleum, fuel cells, etc.) performs tests by their own laboratory-developed methods, thus rendering cross- comparisons of material property data highly questionable. It is extremely important that data generated in a hydrogen environment be done to a standard that reduces variance to a minimum and allows direct comparison of test results from different laboratories. Doing so will assure that all data generated can be used to further our understanding of the hydrogen effects and to make sure components/products designed for hydrogen are the safest and most reliable possible. This paper reviews the results of two 'round-robin' programs conducted by NASA-MSFC. These two programs examined the reproducibility and repeatability of tensile and low-cycle fatigue test results in high-pressure hydrogen environments. The studies indicated that even with the tightest controls available from current commercial standards, the reproducibility (between different laboratories) and repeatability (within a laboratory) results of the tensile tests exhibited five times the variance as in standard ambient air tests. The variance with the LCF tests were on the same order as with air tests, but that was due to the large variation present in the last Interlaboratory air program. The paper concludes with a recommendation for a program that would allow the development of improved test methods, leading to lower variance in the generation of mechanical property data in the future.
    Keywords: Propellants and Fuels
    Type: International Conference for Hydrogen Effects on Material Behavior and Corrosion Deformation Interaction; 22-26 Sep. 2002; Morgan, WY; United States
    Format: text
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