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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2300-2305 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Radiation damage and its recovery process of molecular-beam epitaxy grown AlSb implanted with Ga ions is studied using Raman scattering for Ga ion fluences ranging from 1×1013 to 5×1014 cm−2 and for annealing temperatures ranging from 300 to 600 °C. With increasing fluences the AlSb longitudinal optical (LO) phonon mode shifts to lower frequency and exhibits an asymmetric broadening. Recovery of radiation damages in the ion implanted AlSb is observed after annealing at as low as 300 °C. On the other hand, after annealing at above 500 °C, disordering of the crystalline structure due to the outdiffusion of Sb is observed. The damage states and the recovering behaviors are quantitatively estimated using the spatial correlation model on the LO mode.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 579-585 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recovery process in GaSb crystals with Ga ion implantation and subsequent annealing by rapid thermal annealing (RTA) or furnace annealing (FA) methods are studied by Raman scattering. The intensity of the GaSb LO phonon mode decreases with increasing ion implantation fluence. It is found that the threshold fluence to the amorphization for the Ga ion implanted GaSb is 5×1013 cm−2. It is much lower than that for InP (1×1014 cm−2). In the face-to-face FA, the recovery processes in the Ga ion implanted GaSb are very different above and below the fluence of 5×1014 cm−2. For the 5×1014 cm−2 Ga ion implantation, no recovery is observed. Below 5×1014 cm−2 implantation, the GaSb LO mode intensity increases with increasing annealing temperature and with time up to 400 °C and 15 min, respectively. However, the recovery of damage is very poor compared with that of GaAs, InP, and GaP. On the other hand, in the Si3N4 caped RTA the recovery is observed even for the 5×1014 cm−2 implantation. New modes are observed at around 114 and 150 cm−1 in the implanted and annealed GaSb samples. These two modes are related to Eg and A1g modes of Sb—Sb bond vibrations, respectively, and are produced due to the outdiffusion of Sb atoms. It is found that the face-to-face annealing enhances the outdiffusion of Sb, and that the Si3N4 caped RTA process is superior to the face-to-face FA process for the healing of the damaged layers. These anomalous behaviors are closely related to the weak bond strength of Sb containing materials. The degree of the recovery as a function of annealing temperature, annealing time, and ion implantation fluence is also investigated in both RTA and FA methods.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3164-3170 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In superconductors, cracks (of width w (approximately-greater-than) ξs) are effective in enhancing local supercurrent, and we calculate the size of these supercurrent hot spots as a function of the crack length a and the London penetration depth λ using the two-dimensional (2D) London theory. In the λ→∞ limit and constant injected current density, we show that this 2D solution is also exact for the current flow in a thin film containing a through crack. We argue that large local supercurrents near a surface crack nucleate vortex creation. If flux pinning is weak enough these vortices flow under the influence of the large local Lorentz force. The dissipation so produced can lead to a reduction in observed critical current. If flux pinning is moderate, the first additional vortices nucleated near the crack tip are pinned, in a region we label ρ, the flux pinning zone. In the case of a through crack in a thin film, we then argue that jc(a) reduces as jc(a)/jc(0) ∼ (ρ/a)x (for a/L(very-much-less-than)1), where L is the film width and x =1/2 for the simplest London theory. We compare this theory with the Bean (critical state) model, which predicts that the critical current is (approximately) determined by the cross section available for supercurrent, so that in a film containing a crack, jc(a)/jc(0) ∼ 1 − a/L (ignoring self-field effects). We argue that superconductors with sufficiently weak pinning should obey the hot-spot theory, while sufficiently hard superconductors should obey the critical-state model, and suggest experiments that should illustrate these two limiting cases.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6995-6997 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Hall effect due to spin injection was investigated by using an Al Hall bar attached to a Co/Al planar wire junction. There is observed a significant change in the Hall voltage due to the spin injection when the position of the Hall bar is placed 0.5 μm away from the Co/Al interface. The obtained results were analyzed by taking into account the contributions of the enhancement of the ordinary Hall effect due to a locally increased gradient of the electrochemical potential, and of the extraordinary Hall effect due to the induced nonequilibrium magnetization. The spin diffusion length in Al in the present study is about 1 μm, and the induced difference in chemical potential between up and down spins is about 2.6×10−8 eV. The experimentally evaluated enhancement factor of the ordinary Hall effect is about 1.5, which shows a relatively small contribution to the net Hall effect compared to the extraordinary Hall effect due to the induced nonequilibrium magnetization. © 2000 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6400-6402 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A stress-operated memory device consisting of an ellipsoidal magnetic particle array and an electrostrictive grid is proposed. In the device, the magnetic state of the particle can be controlled only by the magnetostriction effect. Each particle is located at the intersection of the grid and has an in-plane uniaxial anisotropy. A pair of electric contacts is connected to the end of each wire. In the writing process, the driving voltages are simultaneously applied to two pairs of the selected contacts. This allows to apply a local electric field whose direction and amplitude can be regulated by varying the voltage intensity and polarity. The exerting stress on the magnetic particle results in the linear magnetostriction and hence an additional anisotropy energy in the particle. The in-plane total energy minimum, corresponding to the magnetization direction, follows the local electric field. Consequently the magnetization of the single magnetic particle located at the intersection can therefore be selectively switched. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4498-4502 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three series of NdxTbyFe1−x−y−zCoz films have been fabricated for their potential application in magneto-optical recording: (i) x=0–0.20, Tb was adjusted so that the coercivity at room temperature was 5–10 kOe; (ii) x+y=0.28–0.32 with x in the range of 0 to 0.25; and (iii) x+y=0.21–0.23 with x in the range of 0 to 0.17. These films have been characterized both optically and magneto-optically by Kerr hysteresis trace, variable angle of incidence ellipsometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants (n and k), magneto-optical constants (Q1 and Q2), and maximum possible figure of merit (FOM) have been determined at wavelengths of 405, 546, and 633 nm. Results demonstrate that the magneto-optical behavior of NdTbFeCo films is sensitive to the concentration of both Nd and Tb in the film. For samples in the series (i), the addition of Nd into TbFeCo alloys was shown not to enhance their magneto-optic behavior at the short wavelengths. For samples in the series (ii) and (iii), the substitution of Nd improves the magneto-optical performance greatly at blue light. But at red and green wavelengths it has little effect on the magneto-optical properties in samples in the series (iii) or degrades in samples in the series (ii). The maximum enhancement in the FOM is about 25% at x∼10% for blue light. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5670-5670 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes a simple and convenient simulation method, which uses analytical models for mark and beam patterns. The readout signal of optical disk system is obtained by two-dimensional convolution of Gaussian intensity beam pattern and elliptical mark pattern. Then, signal spectrum is obtained by executing a fast Fourier transform algorithm after adding quantitative MO noise sources within bandwidth. For simulation, the two-dimensional distributions of mark reflectivity and beam intensity were digitized, which enabled us to use easily available algorithm routines in digital signal processing. The resolution of the beam and mark patterns can easily be adjusted by changing the number of bits representing the patterns. Also, various noise sources in the MO disk system can be selectively added using random function generator. Simulated signal spectra were compared with experimental results. The parameters used were as follows: laser beam width was 780 nm, NA was 0.55, signal frequency was 9.4 MHz, duty ratio was 38%, and minimum mark dimension was 0.6 μm by 0.75 μm. Simulated C/N ratio was 50 dB, which was very close to the experimental value of 52 dB. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 509-513 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and theoretical studies are reported on formation of primary particles during evaporation of metals into a host gas in an evaporation chamber. The developed theory explains present and previous experimental observations of this process. The dependence of primary particle size on host gas pressure, host-gas molecular weight and source temperature has been explained. Particle thermophoresis has been shown to cause formation of the so-called "smoke shell'' observed surrounding the vapor source. Coalescence of primary particles has been shown not to be an important growth process for the primary particles, although for longer times primary particle coagulation produces the chains of primary particles observed experimentally.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2696-2696 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
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  • 10
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biophysics and Biomolecular Structure 27 (1998), S. 447-474 
    ISSN: 1056-8700
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Physics
    Notes: Abstract In this review we discuss various recent topics that characterize functional magnetic resonance imaging (fMRI). These topics include a brief description of MRI image acquisition, how to cope with noise or signal fluctuation, the basis of fMRI signal changes, and the relation of MRI signal to neuronal events. Several observations of fMRI that show good correlation to the neurofunction are referred to. Temporal characteristics of fMRI signals and examples of how the feature of real time measurement is utilized are then described. The question of spatial resolution of fMRI, which must be dictated by the vascular structure serving the functional system, is discussed based on various fMRI observations. Finally, the advantage of fMRI mapping is shown in a few examples. Reviewing the vast number of recent fMRI application that have now been reported is beyond the scope of this article.
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