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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1767-1770 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the fabrication of micron-sized Hall probes from a Si/SiGe heterostructure. The magnetic field response of the Hall probes shows a very high sensitivity of ∼60 Ω/kG. Below a temperature of 80 K, the Hall probes exhibit a highly linear field dependence of the Hall resistance. The onset of the quantum Hall effect at very low temperatures and high magnetic fields causes only small deviations from the linear field response. We demonstrate the performance of the device as a sensitive local magnetization probe in high-temperature superconducting crystals of Bi2Sr2CaCu2O8. With a linear array of Hall probes we track both the spatial and temporal evolution of the magnetization profile across the crystal. In this way surface and bulk contributions to the overall magnetization can be delineated. © 1999 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1179-1187 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One- and two-detector Doppler broadening measurements performed on low (∼1014 to 1015 O+/cm2) and high dose (∼1017 to 1018 O+/cm2) oxygen-irradiated Si using variable-energy slow positrons are analyzed in terms of S and W parameters. After annealing the low-dose samples at 800 °C, large VxOy complexes are formed at depths around 400 nm. These complexes produce a clear-cut signature when the ratio of S to that of defect-free bulk Si is plotted. Similar behavior is found for samples irradiated with 2 and 4×1017 O+/cm2 and annealed at 1000 °C. After irradiation with 1.7×1018 O+/cm2 and anneal at 1350 °C a 170 nm thick almost-bulk-quality Si surface layer is formed on top of a 430 nm thick buried oxide layer. This method of preparation is called separation by implantation of oxygen. S−W measurements show that the surface layer contains electrically inactive VxOy complexes not seen by electron microscopy. A method is presented to decompose the Doppler broadening line shape into contributions of the bulk, surface, and defect. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3467-3478 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous Si layers were grown by krypton plasma sputter deposition at 310 °C. By pulsation of the substrate potential between 0 and 50 eV, the Kr concentration in the layers could be varied to a maximum of 5.5 at. %. A model which describes trapping of inert gas atoms in the sputtered layer in terms of implantation and trapping, diffusion, growth, resputtering, and gas sputtering is presented. High-resolution electron microscopy, electrode-probe (x-ray) microanalysis, positron annihilation, Raman spectroscopy, Mössbauer spectroscopy, and bending and hardness measurements were performed on the deposited layers. It turns out that the ion assisted growth leads to a strong reduction of open volume defects. The experiments point to the presence of very small Kr agglomerates. From the Mössbauer experiments a lower limit of 250 K for the Debye temperature of the Kr agglomerates is derived. Molecular-dynamic simulations from which the Debye temperatures of Kr mono-, di-, and trimers in amorphous Si can be derived are presented. The simulations indicate the presence of predominantly Kr monomers and dimers. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2725-2729 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the use of a layered foil as a positron rectifying device for transmission geometry positron moderation and remoderation, thereby increasing the efficiency of such devices. Positron transmission through foils consisting of a 10 nm W layer on top of a 100 nm Mo foil has been measured. The measurements are compared with similar results for a 100 nm W foil. A strong rectifying effect with a forward to reverse current ratio of more than 10 is observed making this type of well matched layered foils an obvious candidate for positron remoderation. Retarding energy spectra of the transmitted positrons were obtained and measurements of Doppler broadening and surface branching ratios were performed to further characterize the foils. The obtained transmission results again reveal the discrepancy in positron implantation profiles for thin foils between experiments and existing theory. © 1997 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonhydrogenated diamondlike carbon films have been prepared by dual ion beam sputtering and ion-beam-assisted magnetron. The assistance parameters—ion energy, ion mass, ion flux/atom flux—have been systematically varied, and the films have been characterized by Rutherford backscattering spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, positron annihilation spectroscopy, Raman spectroscopy, and nanoindentation. It was found that the density and the degree of disorder of the films go through a maximum with ion energy, and the void concentration goes through a minimum. Microstructure analysis shows that the films are mostly sp2 bonded, with a maximum of about 16% concentration of sp3 bonding from the largest values of density. The evolution of density with ion flux and energy is consistent with a combined effect of atomic displacements in the film leading to densification, and damage buildup leading to progressive graphitization as the energy is increased. The large hardness/elastic modulus ratios obtained should lead to excellent friction properties.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9029-9036 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved approach is presented for the analysis of positron beam Doppler broadening data. Instead of analyzing the energy-dependent shape parameter, the so-called S(E) data, we combined the shape S(E) and wing W(E) data by plotting them as a trajectory in the S–W plane, using the implantation energy as a running parameter. It is shown that this plot is of particular interest for the qualitative interpretation of the data. Furthermore, it allows the independent determination of the characteristic shape and wing parameters of the different positron trapping layers without the use of a numerical simulation and fitting program. The method and its advantages and limitations are illustrated for three cases: a silicon sample implanted with helium, a metal–oxide–silicon system subjected to a bias voltage and a bare oxide layer on silicon. © 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 70 (1991), S. 3003-3006 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial layers of silicon grown on a Si(100) substrate by molecular-beam epitaxy (MBE) and solid-phase epitaxy (SPE) have been investigated by slow positron beam analysis methods. Results of Doppler broadening measurements revealed that the S parameter of the SPE material is considerably higher than the value measured for the MBE layer, indicative of a higher concentration of open-volume defects in the former material. This was confirmed by measurements of the positronium fraction at elevated temperatures.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5145-5152 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of pure amorphous Si, prepared by ion implantation, has been investigated by variable-energy positron annihilation spectroscopy (PAS) and lifetime measurements of optically generated free carriers. In general, PAS measurements are thought to be sensitive to vacancy-type defects while the carrier lifetime depends on the density of band-gap states (e.g., dangling bonds). The PAS measurements indicate that the density of positron-trapping defects can be reduced by thermal annealing at 500 °C. Concurrent with the removal of structural defects the density of band gap states is reduced as indicated by an increased photocarrier lifetime by a factor of 10. Some material has been implanted with H+ and annealed at a low temperature (150 °C). The hydrogen is expected to passivate electrical defects associated with strained and dangling bonds and indeed the photocarrier lifetime is increased in this material. Moreover, the PAS measurements cannot distinguish this material from 500 °C annealed amorphous Si, indicating that (some of) the electrical defects are associated with positron-trapping, and therefore possibly vacancy-type, structural defects. Finally, both methods have been used to detect small amounts of ion irradiation damage in annealed amorphous Si.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 426-429 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current Ic of several triode-sputtered and laser-ablated thin YBa2Cu3O7−δ films is investigated over the temperature range of 5–85 K. Near the critical temperature Tc it is found that Ic∝(1−T/Tc)γ with γ(approximately-equal-to)1.5–2. The value of γ depends very sensitively on the value determined for Tc. The low-temperature data, for temperatures below about 0.6Tc, can be well analyzed in terms of a proximity-effect model. The effective barrier thickness dN between superconducting parts of the samples is of the order of a few nanometers for all samples studied.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3746-3749 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A time-of-flight (TOF) study of the particles leaving a CuCl target after irradiation by 15 ns laser pulses at 308 nm is performed. It is shown that the ejected species are Cl, Cu, CuCl, Cu2Cl, Cu2Cl2, and Cu3Cl3. The majority of the products consists of CuCl. The TOF spectra can be fitted by the sum of two contributions: a Maxwell–Boltzmann (MB) and a Gaussian-type (G) distribution. The MB distribution has a temperature of T=6000 K for all masses. The average energy and the standard deviation in the energy of the G contributions are typical for every individual product. The results strongly suggest that the MB contribution is due to a single photon-induced process, whereas the G contribution originates from a multiphoton and/or a multistep process.
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