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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5907-5909 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied III-V semiconductor dot samples with Raman microscopy. The samples were fabricated by electron beam lithography and dry etching. The non-resonant Raman scattering can provide direct information on the structure alteration and associated phonon bands. Direct Raman band imaging reveals the uniformity of the GaAs micrometer-sized dot arrays.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2105-2113 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The tin (Sn) diffusion step for producing Nb3Sn-Cu superconducting wire by the external Sn process was modeled in experiments where either pure Sn or a Cu-Sn alloy was plated on sheets of either pure Cu or a Cu-Sn bronze. Each stage of the three-stage solid-state diffusion process was evaluated and it was found that rows of voids are produced in stage I of the process. These voids coarsen in stages II and III and in the worst case they are observed to coalesce and cause complete spalling away of the Sn-rich diffusion layers. Methods for minimizing void formation and possible causes of the void formation are discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 8308-8323 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combination of experimental methods has been employed for the study of Cl2 adsorption and reaction on Si(100)–(2×1). At 100 K, Cl2 adsorption occurs rapidly to a coverage of ∼0.7 Cl/Si. This is followed by slower adsorption kinetics with further Cl2 exposure. Two Cl adsorption states are observed experimentally. One of the adsorption states is terminally bonded Cl on the inclined dangling bond of the symmetric Si2 dimer sites, with a vibrational frequency, ν(SiCl) of 550∼600 cm−1. These bonded Cl atoms give four off-normal Cl+ ESDIAD emission beams from the orthogonal domains of silicon dimer sites. The Si–Cl bond angle for this adsorption configuration is estimated to be inclined 25°±4° off-normal. The second Cl adsorption state, a minority species, is bridge bonded Cl with ν(Si2Cl) of ∼295 cm−1 which produces Cl+ ion emission along the surface normal direction. Both adsorption states are present at low temperatures. Irreversible conversion from bridge bonded Cl to terminally bonded Cl begins to occur near 300 K; the conversion is complete near ∼673 K. LEED studies indicate that the (2×1) reconstruction for the substrate is preserved for all Cl coverages. The most probable Cl+ kinetic energy in electron stimulated desorption, ESD, is 1.1−+0.30.6 eV. A significant adsorbate-adsorbate quenching effect reducing the Cl+ ion yield in ESD occurs above a Cl(a) coverage of ∼0.5 ML (monolayer) due to interadsorbate interactions. The maximum Cl+ yield is about 4×10−7 Cl+/e at an electron energy of 120 eV. Temperature programmed desorption results show that SiCl2 is the major etching product which desorbs at about 840 K.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 111-113 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lamb wave devices based on capacitive micromachined ultrasonic transducers (CMUTs) have been built on 500-μm-thick silicon wafers for frequencies in the vicinity of 1 MHz. CMUTs have been used to both excite and detect Lamb waves in the substrate. This configuration eliminates the need for piezoelectric materials, which are not compatible with the existing integrated circuit (IC) fabrication techniques, and allows easy integration of Lamb wave devices and electronics on the same wafer. Finite element analysis of the devices shows that the lowest order antisymmetric Lamb wave (A0) is the dominant mode in the substrate in this frequency range. This result is also confirmed by demonstration experiments. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2432-2434 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a detailed study of the morphology of pits formed by corrosion of aluminum thin films using an in-plane light scattering technique. We show that the corrosion front of the Al thin film can be treated as a quasi-two-level random rough surface. Based on an elastic diffraction theory, we are able to determine the average depth, the area, and the density of pits, as well as the fractal dimension of the surface. Using the advantages of light scattering, one can quantify the morphological parameters of corroded films in situ and nondestructively. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2311-2313 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the degradation of critical current density (Jc) and irreversibility field (Hirr) of pure and Ti-doped MgB2 bulks by exposing the samples to water for a total of 10, 48, 100, and 124 h. We found that both Jc and Hirr of the samples were degraded by exposure to water, in various degrees depending on the doping level. In the same exposure duration, the Ti-doped samples exhibited a less sensitivity to water, which was confirmed by the less degradation of Jc and Hirr. Our results demonstrate that Ti doping is not only effective in improving the superconducting properties of MgB2 but also in enhancing its chemical stability against water. © 2002 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3320-3322 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work, the realization of AlxGa1−xAs/GaAs two-step barrier diode is presented. Experimental observation on the current–voltage characteristics of the two-step barrier diode is reported. At both room temperature and 77 K, it shows a strong negative differential resistance under forward bias while no similar phenomenon was observed under reverse bias. Such an asymmetric current–voltage characteristic would open the possibility of negative differential resistance in an ac field in the absence of a dc bias. Theoretical simulation and experimental current–voltage characteristics are compared and discussed. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 4040-4050 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of toroidicity-induced Alfvén eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values of vh/vA ((approximately-greater-than)1) and destabilizing for smaller values of vh/vA (〈1), where vh is the hot particle speed and vA is the Alfvén speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measurements.
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  • 9
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal Alfvén eigenmodes (TAE) have been excited by tangential neutral beam injection in the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the Thirteenth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, 1990, Washington, D.C. (International Atomic Energy Agency, Vienna, 1990), Vol. I, p. 9]. Beam emission spectroscopy (BES) has been used to study the radial structure and the poloidal power spectra of these modes. Radial profiles show a global, standing wave structure with a node near r/a=0.6 and a maximum displacement of about 5–10 mm. The cross-phase profiles and the power spectra both imply that the mode is composed of a mixture of components with various poloidal and toroidal mode numbers, as expected for the TAE. Measurements of the poloidal mode spectrum via BES show good agreement with theoretical simulations performed by a nonvariational, kinetic magnetohydrodynamics stability code (nova−k [Cheng, Phys. Rep. 211, 1 (1992)]). In particular, the dominant harmonics in the poloidal spectrum obey the expected relation m+1/2≈q(r)n.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2463-2471 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high-frequency, low mode number toroidicity-induced Alfvén eigenmodes (TAE) [Phys. Fluids 29, 3695 (1986)] are shown to be driven unstable by the circulating and/or trapped α particles through the wave–particle resonances. Satisfying the resonance condition requires that the α-particle birth speed vα≥vA/2||m−nq||, where vA is the Alfvén speed, m is the poloidal mode number, and n is the toroidal mode number. To destabilize TAE modes, the inverse Landau damping associated with the α-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the α particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aid of the nova-k code. Stability criteria in terms of the α-particle beta βα, α-particle pressure parameter (ω@B|/ωA) (ω* is the α-particle diamagnetic drift frequency), and (vα/vA) parameters will be presented for the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the Thirteenth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Crystal City, VA, 1990 (International Atomic Energy Agency, Vienna, in press)], Compact Ignition Tokamak (CIT) [Phys. Scr. T16, 89 (1987)], and the International Thermonuclear Experimental Reactor (ITER) [ITER Documentation Series, No. 21 (International Atomic Energy Agency, Vienna, 1991)].The volume-averaged α-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume-averaged α-particle beta threshold is in the order of 10−4. Typical growth rates of the n=1 TAE mode can be in the order of 10−2ωA , where ωA=vA/qR . Other types of global Alfvén waves are stable in deuterium–tritium (D–T) tokamaks due to toroidal coupling effects.
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