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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7615-7617 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Porous Si (PS) layers are prepared by stain etching in a HF/NaNO2 solution on both p- and n-type crystal Si substrates, and are characterized by photoluminescence (PL), electron paramagnetic resonance (EPR), and infrared absorption (IR) spectroscopy. The PL spectra under 488 nm laser excitation exhibit a strong peak at 680–720 nm for various samples of different substrate parameters and remain stable upon aging in air or γ irradiation; as-etched (∼20 min in air before measurement) and aged (for up to six months) samples show no detectable EPR signal but the γ-irradiated samples show an isotropic g=2.006 signal of peak-to-peak linewidth of 1.1 mT supporting an amorphous Si structure; the IR spectra show both hydrogen and oxygen related IR modes in the as-etched samples and the former decreases with aging time in air while the latter increases. Comparing our results with those of anodically etched PS samples we conclude that: (1) the PL peak position of the stain PS seems to be unique and stable as compared with that of the anodic PS varying in 620–830 nm; (2) the isotropic EPR signal of the stain PS reflects no crystallinity, in contrast with the anisotropic signal of the anodic PS; and (3) obvious oxidation in the as-etched stain PS is also in contrast with the nonobservation of oxygen-related IR modes in the as-etched anodic PS. We discuss the results in terms of structural properties and PL mechanism of PS.
    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 71 (1992), S. 536-538 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Having been exposed to hydrogen plasma, Te-doped GaAs wafers were deposited with metal Ti, to form Ti/n-GaAs Schottky barrier diodes (SBD). It was found that due to hydrogenation the Schottky barrier height (SBH) of the SBD decreases from 0.76 to 0.58 eV and the effective Richardson constant A** decreases from 11 to 0.03 A/cm2/K2. Annealing the hydrogenated SBD at different reverse biases at 100 °C produces SBHs that have a one-to-one correlation with the biases of reverse-bias annealing (RBA), i.e., the SBH can be controlled, within the range 0.58–0.74 eV, by the bias of RBA. When the reverse bias is equal to or larger than 3 V, the SBH and the effective Richardson constant of the hydrogenated SBDs after RBA are very near to those of SBDs without hydrogenation. This means that a RBA with a bias higher than a critical value, 3 V in our case, can remove the effects of hydrogenation, but if the SBD is annealed again without a bias at 100 °C for 1 h or more, its SBH and effective Richardson constant recover their hydrogenated values. The main experimental facts can be explained qualitatively by a simple theoretical model.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5751-5753 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron diffraction has been used to study the magnetic fluctuations and long range order of the Dy ions in single crystals of superconducting DyBa2Cu3O7. The temperature dependence of the rod of scattering, characteristic of 2D behavior, has been measured above and below the 3D Néel temperature (TN (approximately-equal-to) 0.9 K). This rod intensity is observed to increase as the temperature decreases until TN is reached, and then the intensity decreases rapidly below TN. The 2D magnetic correlation length, which is obtained from measurements of the width of the rod, grows continuously with decreasing temperature, then reaches a resolution-limited maximum at the Néel temperature when long range magnetic order sets in. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of (1/2 1/2 0), and the other by (1/2 1/2 1/2). We believe the two types of order occur because the (dipolar) energies for these two configurations are nearly identical. This behavior is analogous to the 2D and 3D magnetic order of Er observed in ErBa2Cu3O7.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5592-5594 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Au/n-Si Schottky barrier (SB) which contains hydrogen has a 0.10 eV lower SB height (SBH) than that without hydrogen. For the hydrogen-containing SB, zero bias annealing (ZBA) decreases the SBH while reverse bias annealing (RBA) increases it. In addition, ZBA and RBA cycling experiments have been made which reveal a reversible change of the SBH within at least four cycles. The annealing temperature of ZBA and especially of RBA influences the SBH. We interpret the above effect in terms of an interaction between hydrogen and metal-semiconductor interface states.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 641-643 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen was incorporated into B-doped p-type crystalline silicon in three different ways: boiling the sample in water, exposing the sample to hydrogen plasma, growing silicon in a hydrogen atmosphere. Al-contact Schottky barrier diodes were made on both the hydrogenated and unhydrogenated samples. It was found that the Schottky barrier height (SBH) is increased due to the hydrogenation. The current-voltage measurement showed an increase of 0.06–0.10 eV in the effective SBH and the activation energy measurement revealed an increase of 0.07–0.09 eV in the SBH under a forward bias of 0.15 V. If the silicon grown in a hydrogen atmosphere was thermal annealed at 650 °C to drive out hydrogen before Schottky metallization, then the SBH approached that of the unhydrogenated sample. It is demonstrated that the SBH in Al/p-Si can be increased with hydrogen incorporated in silicon.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 90-92 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Shubnikov–de Haas oscillations of the two-dimensional electron gas in semimetallic undoped Ga1−xAlxSb/InAs single quantum wells with compositions x=0.1,0.2,0.5,0.8,1.0 are studied by X-band electron paramagnetic resonance spectroscopy in the 4–20 K temperature range. The thermal equilibrium carrier concentrations vary from 4×1011 cm−2 for x=0.2 to 1×1012 cm−2 for x=1.0; from the temperature dependence of the Shubnikov–de Haas oscillations amplitudes in the 1–2 T magnetic field range the effective mass is determined to 0.026m0. Photoexcitation, with a low-energy threshold of 0.7 eV, gives rise to a negative persistent photoconductivity (NPPC) for alloy compositions x≥0.2; no NPPC is observed for x=0.1.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1830-1832 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a study on gamma irradiated porous Si. The electron paramagnetic resonance study on porous Si irradiated by gamma rays shows that the observed signals come from an intrinsic defect, a Si dangling bond, at the interface of Si/SiOx in porous Si. The photoluminescence measurements show that the gamma irradiation not only increases the intensity of the photoluminescence but also greatly improves its stability. The spectra of the Fourier transform infrared absorption show that the gamma irradiation is an effective method for accelerating oxidation of porous Si. All experimental results can be explained by the increase of the oxidation layer thickness which decreases the nonradiative recombination probability of electron-hole pairs.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In photoluminescent porous Si layers is observed a dominant intrinsic EPR signal of trigonal symmetry with g(parallel)=2.0023±0.0003 and g⊥=2.0086±0.0003 as principal g values. This EPR signal can be identified with Si dangling bonds by its symmetry and characteristic g values. The rotation pattern of the EPR signal indicates that the axial directions of the dangling bonds are distributed in all the four 〈111〉 crystal axes of the original silicon lattice. These results can be exclusively explained by the existence of the crystalline Si phase with retention of the original crystal orientation in porous Si. The dangling bond formation is found to be closely related to the surface oxidation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2320-2322 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of GdBa2Cu3O7 superconductor were grown in situ on MgO single-crystal substrates under different substrate temperatures (Ts). When Ts=800 °C, the films were epitaxially grown with the c axis perpendicular to the film surface. The growth quality was very good, but the zero resistance critical temperature (Tc0) was only 85 K and the transition width (ΔTc) was 1.5 K. When Ts=670 °C, some of the films were epitaxially grown with the c axis perpendicular to the film surface. Some were mainly c axis oriented with a small amount of (110) and a-axis orientation. The growth quality was relatively poor, but they had Tc0 of 89–91 K and ΔTc of 0.6–1 K.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 13 (1991), S. 157-163 
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Two approximate formulae to calculate the eigenvalues of pure quadrupole interaction in Mössbauer effect studies have been proposed and the eigenvalue coefficients in the formulae have been given for various excited states and ground states of the nucleus with different spin. All the eigenvalues of pure quadrupole interaction between both excited state and ground state of nucleus with spinI=3/2÷9/2 and the electric-field gradient with different asymmetry parameter (η=0÷1.0) have been calculated by these formulae. The results show that the accuracies in all the calculations are more satisfactory or same in comparison with those obtained by the formula of Shenoy and Dunlap, especially when the asymmetry parameter of electric-field gradient is larger than 0.8 for the nucleus with spinI=5/2.
    Type of Medium: Electronic Resource
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