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  • Institute of Physics  (109)
  • National Academy of Sciences  (48)
  • American Institute of Physics (AIP)  (23)
  • Copernicus  (12)
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetism in ultrathin (1–10 ML) Fe films grown on Cu(100) has been studied by spin-polarized secondary electron emission spectroscopy. The variation of the magnetization with temperature and oxygen adsorption was investigated for various film thicknesses. The orientation of the magnetization for films between 5 and 6 ML thick switches reversibly between perpendicular (at low temperature) to in-plane (at high temperature). The switching transition temperature decreases with increasing film thickness, and is accompanied by a loss of long-range order over a range of 20–30 K. The transition is attributed to the temperature dependence of the perpendicular anisotropy. The effect of oxygen adsorption onto films with perpendicular remanence is to first suddenly turn the magnetization into the plane at a critical coverage, and then to kill the magnetization gradually with continued exposure. This indicates that the uniaxial surface anisotropy at the Fe-vacuum interface plays a major role in the magnetization of the film.
    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 87 (2000), S. 6788-6790 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For sputtered Co57Mn43/Si film samples with different ferromagnetic thickness, the spectra of the complex magneto-optical polar Kerr rotation and optical constants were ex-situ measured. For 5 nm-thick Co57Mn43 film, the Kerr rotation around 4.3 eV was enhanced by a factor of about 10 times with lower loss of the signal intensity as compared to the thick film. Numerical calculations show that the enhancement effect is attributed to an interplay between optical properties of Co57Mn43 and substrate Si that has a strong interband transition (E2) near 4.3 eV. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3332-3337 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: First-order Raman scattering of hexagonal GaN single crystal films deposited on sapphire substrate by low pressure metal organic chemical vapor deposition is studied between 78 and 870 K. The temperature dependence of the five GaN Raman modes is obtained. Both the linewidth and Raman shift exhibit a quadratic dependence on temperature in our measured temperature range. Excellent agreement was found between the experiment data and calculated results based on a model involving three- and four-phonon coupling. Our results indicate it is necessary to include the contributions of both the thermal expansion and four-phonon terms in the four-phonon anharmonic processes to explain the change of Raman shift and linewidth with temperature. In addition, a decrease in the splitting between the longitudinal optical and transverse optical phonons with increasing temperature was also observed. From these data a weak nonlinear decrease of the transverse effective charge with increasing temperature is derived. The comparison of the transverse effective charge eT* at room temperature was made between experimental data and theoretical calculations by a pseudopotential expression and bond orbital model. Good agreement between theory and experiment is achieved. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3744-3747 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magneto-optical and optical properties of GdFe single layer films, which are covered with a thin Si3N4 layer, were studied in the visible wavelength region. A Kerr rotation peak and a reflectivity drop were observed near 4.1 eV in GdFe alloyed films and attributed to the Gd element. Compared with the single thick GdFe film, the Kerr effect of SiN/GdFe bilayers was enhanced, due to the optical interference between Si3N4 and GdFe. The Kerr rotation of GdFe films showed a nonlinear function of the compositions in the whole measured wavelength range. Magneto-optical measurements directly evidence the spin–flip in the GdFe films as the Gd content increased from 20.7 to 24.2 at. %, which showed advantages over conventional magnetometry. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7991-8006 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We measure the current–voltage and electroluminescence characteristics of single-heterojunction, vacuum-deposited organic light-emitting devices (OLEDs) over a wide range of materials, temperatures, and currents. We find that the current is limited by a large density of traps with an exponential energy distribution below the lowest unoccupied molecular orbital. The characteristic trap depth is 0.15 eV. Furthermore, in metal–quinolate-based devices, electroluminescence originates from recombination of Frenkel excitons, and its temperature dependence is consistent with the excitons being formed by Coulombic relaxation of the trapped electrons with holes injected from the counter electrode. By semiempirical molecular orbital modeling, we find that the trap distribution obtained from the current–voltage characteristics is consistent with a distribution in the metal–quinolate molecular conformations which result in a continuous, exponential distribution of allowed states below the lowest unoccupied molecular orbital. We discuss the implications of the intrinsic relationship between electroluminescence and current transport in OLEDs for the optimization of efficiency and operating voltage in these devices. © 1996 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3953-3959 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pt/Co multilayers sputter-deposited in Ar and Xe ambients, and periodic multilayers composed of specific combinations of Pt, Pd, and Co layers, were grown to study the effects of energetic backscattered Ar neutrals on the interface structure. The effects were correlated with the magnetic and magneto-optical properties with emphasis on the perpendicular magnetic anisotropy, K⊥. Films were characterized by high-resolution transmission electron microscopy, x-ray diffraction including grazing incidence geometry, and magnetic circular x-ray dichroism techniques as well as by standard magnetic and magneto-optic methods. It is found that the perpendicular magnetic anisotropy is extremely sensitive to the degree of intermixing, sharp interfaces yielding the largest anisotropy. The three to fourfold difference in K⊥ found between Ar and Xe sputtered films can be directly correlated to the magnitude of the orbital moment contribution 〈LZ〉 in the Co. This orbital contribution is found to be strongly sensitive to the interface sharpness in the films. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1332-1334 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used high-resolution photoemission spectroscopy to search for a proximity effect induced superconducting gap in gold overlayers on c-axis single crystals of Bi2Sr2CaCu2O8 and a-axis thin films of YBa2Cu3O7. These two junction types give us a representative sampling of very well characterized near-ideal interfaces (gold/c-axis Bi2Sr2CaCu2O8) and junctions in which the geometry more strongly favors the existence of the proximity effect but the interfacial quality may not be as ideal (gold/a-axis YBa2Cu3O7). In neither of these junction types did we observe any evidence for a proximity effect induced gap, and we place an upper limit of approximately 5 meV on its existence in the junctions that we have studied.
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution photoemission has been used to probe the electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interface formed by a low-temperature (20 K) gold evaporation on cleaved high quality single crystals. We find that the metallicity of the EuBa2Cu3O7−δ substrate in the near surface region (∼5 A(ring)) is essentially destroyed by the gold deposition, while the near surface region of Bi2Sr2CaCu2O8 remains metallic. This has potentially wide ranging consequences for the applicability of the different types of superconductors in real devices.
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  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic structure of bulk, and, for the first time, thin-film samples of the new class of high Tc Bi2Sr2CaCu2O8+δ superconductors, is investigated by photoemission spectroscopy using synchrotron radiation. Ar+ sputtering and Rb deposition result in disrupted Bi O bonds and subsequent change in the valency of Bi, while oxygen adsorption or annealing in oxygen is found to restore the Bi O bonds. The results also show that adsorbates of O2 and/or Rb readily give rise to a number of new oxygen states in the valence band of Bi2Sr2CaCu2O8+δ. The Ar+-sputtered film is found to be more sensitive to adsorbates of O2 and Rb than the scraped bulk sample, as monitored by the Bi 5d core shifts and the oxygen-induced valence-band states.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2563-2565 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface structure of Bi2Sr2CaCu2O8+δ has been studied using low-energy electron diffraction (LEED). Sharp diffraction spots indicative of a well-ordered surface are observed. The LEED patterns unequivocally show that this type of material preferentially cleaves along the a-b planes of the nearly tetragonal unit cell. A superstructure extending along one of the axes in the a-b plane (b) is found to have a periodicity of 27±0.5 A(ring), in good agreement with earlier studies of the three-dimensional crystal structure. We conclude that the superstructure at the surface is nonlocal in character and reflects the long-range superlattice of the bulk along the b axis. Intensity modulations of the diffraction spots oriented along the b axis are also reported and discussed in terms of the cell dimension of the unit cell along the b axis.
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