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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 387-396 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Proper gettering and annealing processes allow construction of silicon p-n junctions whose current-voltage characteristic either completely obeys the Shockley equation (ideal junctions) or, for reverse bias, has three components (almost ideal junctions): a voltage-independent term, which may be much smaller than the diffusion saturation current, a generation-recombination contribution, and an ohmic component. The last two currents are due to defect centers that have the same activation energy and which are electrically neutral. In preceding works it has been shown that such an experimental finding may be ascribed to four-state traps, i.e., to defect centers that may be empty of carriers, or filled by an electron or a hole, or both, and which are created by localized states, with different positions and energy levels, due to the oxygen. In the present work an experimental system for measuring, at 0±0.05 °C, the current transients produced in almost ideal junctions by changes of the reverse-bias voltage, and an analysis method for performing the spectrometry of such transients are described. It is found that these last a few hours and that they are composed of four exponential terms whose relaxation times range from tens to a few thousands of seconds. Finally, it is shown that such experimental results also can be ascribed to the preceding defect centers generated by SiyOx clusters of a few hundred atoms of oxygen put near the junction interface, which emit carriers through a tunnel-assisted thermal emission.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interplay between material microstructure and magnetic hysteresis is studied in rapidly quenched Si–Fe alloys. Two ribbons of different average grain dimension 〈s〉 (35 and 160 μm) were prepared by annealing at different temperatures and studied through two independent approaches: Barkhausen noise measurements, and Preisach analysis of static and dynamic hysteresis loops. In order to monitor the effect of demagnetizing fields on the magnetization process, the strips were progressively shortened from 30 to 10 cm. The correlation length of a domain-wall jump was estimated through the analysis of Barkhausen jump distributions versus apparent permeability. The correlation length of the coherent magnetization reversals controlling excess dynamic losses was estimated through the Preisach analysis of dynamic hysteresis loops. In the sample with lower 〈s〉, both the Barkhausen and the dynamic loss correlation lengths are comparable to 〈s〉, showing that a single structural feature governs all aspects of magnetization reversal. Conversely, in the high 〈s〉 sample, the ribbon thickness competes with 〈s〉 in controlling static and dynamic magnetization processes. © 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 85 (1999), S. 4355-4357 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conditions under which relaxation dynamics in the presence of quenched-in disorder lead to rate-independent hysteresis are discussed. The calculation of average hysteresis branches is reduced to the solution of the level-crossing problem for the stochastic field describing quenched-in disorder. Closed analytical solutions are derived for the case where the disorder is characterized by Wiener–Lévy statistics. This case is shown to be equivalent to the Preisach model and the associated Preisach distribution is explicitly derived, as a function of the parameters describing the original dynamic problem. © 1999 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hysteresis, power losses, and the Barkhausen effect are investigated in an Fe-based highly magnetostrictive amorphous material, as a function of applied stress. By means of the static and dynamic Preisach model, and of existing theories of the Barkhausen effect, the results are shown to be compatible with the existence of a characteristic structural length δc, playing a role similar to that of grain size in crystalline materials. At low applied stresses, where the magnetization process is dominated by quenched-in stresses σi, δc is identified with the typical wavelength of σi fluctuations. The theoretical analysis leads to the estimate δc∼70–100 μm and 〈σi〉∼3.5 MPa. © 1999 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interplay between activation volumes and microstructure is investigated in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 (Finemet) alloys. Experiments are performed beyond the Curie point of the amorphous matrix, where relaxation effects are relevant. Measurements are analyzed within a theoretical framework where hysteresis and relaxation phenomena are jointly described. In highly crystallized samples magnetization processes are characterized by a unique length scale. In poorly crystallized samples the system behavior is controlled by a distribution of characteristic volumes related to structural disorder. © 2001 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The connection between hysteresis phenomena and free energy metastable states in magnetic systems is discussed. A random free energy model is introduced, which leads to a stochastic differential equation for the evolution of magnetization in time. We show that the solutions of this equation are equivalent to the Preisach model of hysteresis. The analytical form of the Preisach distribution is calculated. © 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 78 (1995), S. 2504-2508 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results obtained from measurements and spectroscopic analysis of current transients induced in almost ideal silicon n+-p junctions by infra-red stimulation are reported. In particular, by illuminating a reverse biased junction by means of an infra-red emitting diode for a few seconds, a current transient is generated which, at 0 °C, lasts several hours. This can be decomposed, by means of a proper spectroscopic method, into a sum of four exponential contributions with time constants ranging from tens up to thousands of seconds. Similar dark current transients were already obtained for the same junctions when they were stimulated by a change of the reverse bias voltage, without any optical excitation. The spectroscopy of both optical and voltage induced current transients gives four exponential components with the same time constants. Both the dark current and the photocurrent transients are ascribed to the same SiyOx clusters containing hundreds of Si atoms and four types of single energy level defect centers with different localization. While the voltage induced current transients implicate the activation of such defect centers in the p-region near the n+-p interface only, those due to the photostimulation produce their activation throughout the whole n+ region as well. This fact leads to much greater values for the transient photocurrent in comparison to those induced by voltage changes and, as a consequence, to greater reliability and accuracy in the measurements and in the results obtained from their analysis. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6042-6046 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Magnetic circular dichroism (MCD) of trivalent rare earth doped lithium niobate crystals is reported for the first time. Magneto-optical signals of Nd3+ and Yb3+ ions have been studied at 2 K as a function of the magnetic field strength up to 5 T. This study allows the identification of the Zeeman sublevels of these ions, which can be labeled by irreducible representations (Γ4, Γ5, or Γ6), so that the sign and allowance of transitions can be predicted. From the dependence of suitable MCD spectral lines on the magnetic field strength, the effective gyromagnetic factor of the ground state has been determined for both ions: (gNd)(parallel)=1.4±0.1 and; (gYb)(parallel)=4.7±0.1. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1431-1434 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new technique for the optical spectroscopy of adsorbed molecules is introduced. It is based on the detection of the phonons emitted during nonradiative relaxation. A high sensitivity was achieved by using superconducting tunnel junctions as detectors. A light power of the order of 1 μW was sufficient for the spectroscopy of submonolayers of tetracene. Molecules deposited on a cold substrate had a spectrum similar to the one of isolated molecules in a solvent. Deposition, or annealing, at room temperature, however, yielded spectra like those of single crystals.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4774-4776 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A vector model of magnetic hysteresis in biaxial anisotropy structures is presented, in which magnetoelastic effects are explicitly taken into account. The magnetization vector of individual grains is forced to lie along one of the easy axis, and jumps from one easy direction to another one controlled by the sum of the external field and magnetoelastic energy. Hysteresis effects are described by an energy barrier opposing magnetization switching and the total response of the system is obtained by averaging the local magnetization over all grains. Model predictions are compared with experimental results on the hysteresis properties of Si–Fe alloys under compressive stress. © 2000 American Institute of Physics.
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