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  • 1
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The heavy-hole and light-hole excitons of a CdTe epilayer, pseudomorphically grown on an InSb epilayer by molecular beam epitaxy, are studied with a diamond anvil cell as a function of applied hydrostatic pressure via photoluminescence (PL) and photomodulated reflectivity (PR) spectroscopies. They are compared with the excitonic features in the simultaneously measured PL spectra of a sample of bulk CdTe. Under applied pressure, the lattice mismatch-induced splitting between the light-hole and heavy-hole related transitions increases in a continuous and reversible manner because of the additional pressure-induced compression due to the difference in the compressibilities of CdTe and InSb. The unusually large strain sustained by the CdTe epilayer under pressure is discussed in the light of various models. The PR signal vanishes after the InSb epilayer goes through a structural phase transition at approximately 20 kbar, while the PL signal persists until it is irreversibly quenched by the CdTe epilayer undergoing a structural phase transition at approximately 30 kbar. For pressures between 20 and 30 kbar, the behavior of the CdTe epilayer is similar to that of the bulk sample; the strain appears to have been relaxed due to the structural phase transition which has taken place in InSb. Values of the first- and second-order pressure coefficients for bulk CdTe and for the CdTe epilayer as well as values of the hydrostatic and shear deformation potentials are obtained at 14 and 80 K and compared with previously quoted values.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2719-2722 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The volume dependence of the x-ray Debye temperature in aluminum at high pressure up to 6 GPa was measured with high-energy synchrotron radiation at the National Laboratory for High Energy Physics. High-pressure high-temperature diffraction experiments were carried out by use of a multianvil press system with the energy-dispersive diffraction method. The Debye temperature was determined from the integrated intensity ratio at different temperatures. In order to avoid the intrinsic anharmonic effects and the influence of the energy shift for the Bragg diffraction due to the thermal expansion, constant volume was maintained in a sample by controlling the pressure at elevated temperatures. The interpolated values of the Debye temperature and the Grüneisen parameter of the atmospheric volume were θD0 =367 K and γ0 =3.0, respectively. Excellent agreement was found upon comparison with the published results of conventional experiments.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The specific contact resistance ρc of non-alloyed ohmic metals (Mo/Au and WSix) to p-type GaAs is evaluated by transmission line method (TLM) patterns for various doping concentrations from 8×1018 to 1021 cm−3. The obtained specific contact resistance ρc, less than 10−8 Ω cm2, to metalorganic molecular beam epitaxy grown C-doped ( 1021 cm−3) GaAs is the lowest reported value. From the application point of view for the emitter electrodes of PNp type (two-dimensional electron gas base) heterojunction bipolar transistors, the specific contact resistance of a refractory metal, or the sputter-deposited WSix (x=0.45), is also studied. By reducing the growth temperature of molecular beam epitaxy from 600 to 450 °C and enhancing the As4/Ga flux ratio to 15, a nondiffusive heavily Be doped (1020 cm−3) GaAs is obtained. The specific contact resistance of the WSix to this sample is less than 10−6 Ω cm2. The obtained specific contact resistance can be well explained by a simple modeling based on the tunneling transport of light holes. Secondary ion mass spectroscopy analysis of the depth profile under heat acceleration shows a small diffusion of dopants for Be doped (1020 cm−3) GaAs and C-doped (1021 cm−3) GaAs. In addition, the specific contact resistance ρcISO of the isoheterojunction (p+GaAs/p+AlxGa1−xAs) is also evaluated by TLM patterns.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 334-338 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Co/Pd multilayered films exhibit large perpendicular magnetic anisotropy and have attracted attention as new materials for recording media and for other applications. The coercivity (Hc), however, is small in as-sputtered films. We have found that Hc increased markedly with the atmospheric annealing at 300 °C to 2 kOe, and studied the change in film structure and reason of the increase in Hc with the annealing. The rf magnetron sputtering method was employed in fabricating the films. Film structure changes were observed by x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, energy dispersive x-ray spectrography, and atomic force microscopy. The increase in Hc was observed only in the atmospheric annealing, and not in the vacuum-annealing. The internal structure of films after the atmospheric annealing at 300 °C consisted of columnar parts that had the multilayered structure that undertook vertical magnetization and column boundaries being surrounded by Co oxides. As a consequence, domain wall binding occurs in the segregated areas of the oxides in the column boundaries, thereby increasing Hc.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2532-2534 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: For the first time, ZnSe epitaxial layers grown by molecular-beam epitaxy are shown to exhibit large contrast, low power, and extremely long-term stable thermally induced absorptive optical bistability. It is observed over a wide temperature range between 169 K and RT, with a strongly variable loop width and a switch-back adjustable to be less than 50% of the respective switch-down value. Critical slowing down as well as switch-down times are studied in dependence of the excess over the switch-down intensity values.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5630-5635 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Comparative photoluminescence and excitation spectra of ZnSe/GaAs epilayers grown by molecular beam epitaxy (MBE) and hot-wall epitaxy (HWE) show likewise features in the exciton energy regime. Two strain-split components of the free exciton are observed, as well as characteristic sets of transitions from or into ground and excited states of acceptor- and donor-bound excitons. However, all respective lines are shifted to lower energies in the HWE samples, due to the increased thermally induced strain as a consequence of the substrate temperatures being enhanced compared to the MBE growth. Whereas the dominant donors are of the same nature in both kinds of samples, specific acceptor centers are incorporated in the HWE films. Although the MBE-grown layers are of superior quality, it is shown that HWE under optimized growth conditions is a cheap and useful alternative to obtain ZnSe epilayers of reliable properties.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2449-2455 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A detailed experimental investigation of plasma fluctuation and its modification due to radial electric field effects, both its shear and curvature, has been carried out on the Current Sustained Torus IV at Nagoya University [Takamura et al., J. Plasma Fusion Res. 74, 38 (1998)] through measurement with an array of Langmuir probes. The observed statistical dispersion relation indicates a drift-wave-type turbulence. An examination of the radial electric field shear and curvature effects on the fluctuations as well as comparisons to theoretical predictions are presented. The decorrelation of turbulence is found to be influenced by the radial electric field shear in our experiment. A modification of the poloidal correlation length and the two-poloidal-point coherency due to the radial electric field has also been identified. Nonlinear analysis of quadratic mode coupling indicates that the radial electric field can affect the fluctuation amplitudes by modifying the coupling between different spectral components of the fluctuations. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3288-3300 
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The frequency dependence of the tokamak plasma response to the externally applied rotating helical field was investigated by measuring the radial profile of the perturbation field with small magnetic probes which were inserted in the plasma. The experimental results are discussed, directly comparing with the generally accepted linear theory, and taking into account the E×B drift and diamagnetic effect of the plasma. It was found that the experimental results are in good agreement with the simple linear analysis based on the single helicity approximation in a cylindrical geometry, except for the ergodic region, which comes from the overlapping of several sideband components of the perturbation. It is also found that the radial component of the perturbation field is still amplified inside the resonance surface (r〈rs), even when a partial shielding takes place at r(approximate)rs. © 2000 American Institute of Physics.
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7209-7212 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Co–P powders were produced by chemical reduction. The powders had a spherical shape with an average diameter of about 1 μm. X-ray diffraction and differential scanning calorimetry studies confirmed that the powders were amorphous. The amorphous powders showed higher saturation magnetization than the crystalline counterparts. Heat treatment of the powders above the crystallization temperature resulted in the formation of fcc Co, hcp Co, and Co2P phases. The saturation magnetization of the annealed powders monotonically decreased as the annealing temperature increased. On the other hand, the coercivity of the annealed powders rapidly increased with increasing annealing temperature. The powders annealed at 600 °C had a saturation magnetization of 100 emu/g with a coercivity of 500 Oe. © 2000 American Institute of Physics.
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1979-1983 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This study reports the construction and working of a sintered diamond anvil high-pressure cell for performing electrical resistance measurements using a four-probe method at cryogenic temperatures. The apparatus has been designed to minimize the pressure shift during the cooling cycle from room temperature to 1.2 K. Pressure is calibrated using the pressure dependence of the superconducting transition temperature (Tc) of Bi to 50 GPa. The usefulness of the apparatus is demonstrated by electrical resistance and Tc measurements on Se and Zr up to 60 GPa.
    Materialart: Digitale Medien
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