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  • 1
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Epitaxial growth of AlAs-InAs short-period superlattices on (0 0 1) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, non-destructive means for detecting and characterizing the occurrence of compositional modulation. Systematic variations in the compositional modulation due to the structural design and the growth conditions of the short-period superlattice are characterized by routine mapping of the lateral satellites.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9591
    Keywords: Cold fusion ; palladium ; deuterium ; ion implantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Deuterium was introduced into palladium at atomic ratios greater than one by means of ion implantation at cryogenic temperatures, and a search was made for energetic charged particles from D-D nuclear reactions. Concentrations as high as 1.6 D/Pd were produced by 10 keV implantation at temperatures of 41 and 81 K, and the occurrence of lattice supersaturation in the Pd deuteride was indicated by a new, low-temperature stage of D redistribution. Fifteen hours of observation at low temperatures yielded no indication of energetic charged particles due to the reaction D(d,p)T or other nuclear processes. This result implies an approximate upper bound of 10−21 events/s per D atom on the reaction rate in the supersaturated deuteride. Negative results were also obtained for D-implanted zirconium and titanium.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3421-3423 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Al0.48In0.52As monolayers (ML) are inserted at the binary-compound interfaces of (AlAs)2 ML(InAs)2 ML short-period superlattices (SPSs) during growth on (001) InP. The insertion of Al0.48In0.52As interlayers greater than 2 ML thick tends to suppress the phase separation that normally occurs during molecular beam epitaxy of the SPS. The degree of suppression is a sensitive function of both the monolayer-scale thickness, and the intraperiod growth sequence, of the interlayers in the SPS. Given this sensitivity to monolayer-scale variations in the surface-region composition, we propose that cyclical phase transition of the reconstructed surface initiates SPS decomposition. © 2001 American Institute of Physics.
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon (a-tC) films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thin a-tC films (0.1–0.2 μm) were deposited at room temperature. The intrinsic stress in these films (6–8 GPa) was relieved by a short (2 min) anneal at 600 °C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 μm thick have been grown that are adherent to the substrate and have low residual compressive stress (〈0.2 GPa). The values of hardness and modulus determined directly from an Oliver–Pharr analysis of nanoindentation experimental data were 80.2 and 552 GPa, respectively. We used finite-element modeling of the experimental nanoindentation curves to separate the "intrinsic" film response from the measured substrate/film response. We found a hardness of 88 GPa and Young's modulus of 1100 GPa. From these fits, a lower bound on the compressive yield stress of diamond (∼100 GPa) was determined. © 1997 American Institute of Physics.
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results from the first studies of electric-field effects on optical transitions in visible-band-gap InGaP/InAlGaP multiple-quantum-well (MQW) structures. These structures, grown at 775 °C by metalorganic vapor phase epitaxy on (100) GaAs substrates misoriented 6° towards P(111〉〈111〉A, consist of nominally undoped MQWs surrounded by doped In0.49Al0.51P cladding layers to form p-i-n diodes. The Stark shifts of various allowed and forbidden quantum-well transitions were observed in bias-dependent electroreflectance spectra of In0.49Ga0.51P/In0.49(Al0.5Ga0.5)0.51P MQW samples with 10-nm-thick layers. We find the magnitude of these shifts to depend on the details of the Mg doping profile, confirming the importance of Mg diffusion and unintentional background doping in these materials. Our results show that (InAlGa)P materials are promising for visible-wavelength electro-optic modulator applications.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 669-671 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Growth of InAs/AlAs short-period superlattices on appropriately miscut (001) InP substrates is shown to alter the microstructure of composition modulation from a two-dimensional organization of short compositionally enriched wires to a single dominant modulation direction with wire lengths up to ∼1 μm. The effects of miscut are interpreted in terms of surface step orientation and character. The material is strongly modulated and exhibits intense optical emission. The one-dimensional modulations appear potentially useful for new devices that take advantage of the preferred direction formed in the growth plane. © 2000 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1534-1536 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have directly measured the stress evolution during metal-organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to determine directly a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained AlxGa1−xN grown on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2059-2061 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cavities formed in Si and Ge and their alloys by He implantation and annealing are demonstrated to have a strong short-range, attractive interaction with dislocations, with a binding energy calculated to be (approximately-greater-than)100 eV when they overlap. Cavities can alter the relaxation of strained Si86Ge14 layers on Si in several ways: cavities placed at the interface enhance relaxation rates by increased nucleation of misfit dislocations, reduce the number of dislocations protruding into the substrate, and may increase relaxation at thermodynamic equilibrium.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 587-589 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Metalorganic vapor phase epitaxy (MOVPE) is used to grow unicompositional quantum-well (QW) structures, in which the QW and barrier layers are composed of ordered and disordered GaInP, respectively. Transmission electron dark-field micrographs reveal abrupt interfaces between highly ordered QWs and disordered barriers, with no evidence of defect formation. Low-temperature photoluminescence from the structures exhibits relatively broad emission peaks, with emission energy increasing with decreasing QW thickness. The dependence of emission energy on well thickness can be described by a finite square well model only when a type-II band alignment is taken for the heterostructure, in which the conduction band edge of the ordered GaInP QW lies about 135–150 meV below that of the disordered barrier material. These results demonstrate a high degree of control over the ordering process in MOVPE, such that quantum size effects can be realized solely through disorder-order phenomena. Further, the data provide strong support for a type-II (spatially indirect) recombination transition between ordered and disordered GaInP.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dual ion implantation of titanium and carbon into nickel was shown to produce an amorphous layer with exceptionally high strength and hardness and substantially improved tribological properties. Indentation testing at submicrometer penetrations combined with finite-element modeling permitted quantification of the intrinsic elastic and plastic properties of the amorphous layer, which was found to have a yield strength near 5 GPa. During unlubricated sliding contact with a steel pin, the implantation treatment reduced friction, suppressed adhesion-and-fracture wear, and reduced wear depth. These tribological effects may enhance the performance and lifetime of microelectromechanical systems constructed from nickel.
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