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  • American Institute of Physics (AIP)  (12)
  • 2000-2004  (5)
  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6536-6538 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Following a method proposed by Divin and Modovets [Sov. Tech. Phys. Lett. 9, 108 (1983)], we have measured at millimeter waveband the intrinsic noise temperatures TN of YBa2Cu3O7−δ Josephson junctions or dc superconducting quantum interference devices (SQUIDs) fabricated on SrTiO3, yttria-stabilized ZrO2, or Si bicrystal substrates. Over wide ranges of physical temperatures TP and the junction's normal resistance RN, it was found that TN follows TP pretty well. This indicates that the intrinsic noise in the devices is dominated by Johnson noise. TN was also measured in cases where there is external magnetic field applied, or where there is another microwave radiation like the local oscillator in a mixer. The magnetic field or microwave radiation does not seem to affect TN in any appreciable way. To estimate the high frequency performance of the junctions on Si bicrystal substrates, direct irradiation by a far infrared laser at 1.81 THz is carried out and the clear first Shapiro step is observed. © 1996 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4977-4979 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magneto-optical Kerr spectra of ultrathin Co films grown on Cu(001) surfaces have been measured in situ. The growth mode and the crystal structure have been investigating by reflection high-energy electron diffraction observation. A 20-A(ring)-thick fcc Co grown on Cu(001) had a lateral lattice constant of 3.59±0.01 A(ring), which was about 1.4% expanded compared with that of the bulk fcc Co. There was a remarkable difference above 4 eV in ωσyz spectra between 20- and 1000-A(ring)-thick films. ωσyz spectra for 20-A(ring)-thick Co film showed a resonance-type structure at around 5 eV. It is considered that the structure is caused by the lower energy shift of the 1→6 interband transitions due to the narrowing of the 3d bands. © 1996 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. 3740-3744 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using c-axis-oriented oxygen-deficient YBa2Cu3O7−δ film deposited across a low-angle step on a SrTiO3 substrate, we successfully demonstrated intrinsic Josephson effects. In addition to several voltage jumps of large amplitudes (a few millivolts) and remarkable hysteresis on the dc current–voltage curves, we observed upturns on the current–voltage curves under microwave irradiation which appeared at increasingly high voltages with increasing microwave power. We proposed to explain this observation in terms of high-order microwave-induced Shapiro steps. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6064-6066 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optimum junction resistance and minimum tunnel magnetoresistance (TMR) ratio required for high density and high performance magnetoresistive random access memory (MRAM) devices with a TMR cell plus field effect transistor (FET) switch architecture are discussed by taking into account the variation of FET resistance causing noise. This implies that a TMR ratio over 25% at a 400 mV bias voltage and junction resistance of several tens of kilo-ohms for TMR cells are required with a signal voltage of 30 mV and a sense current of 10 μA, which leads to about 10 ns read time. This large magnetoresistance ratio at the elevated bias voltage requires low bias voltage dependence of TMR for the MRAM devices. In order to try to meet this requirement, double tunnel junctions were fabricated which possess the central ferromagnetic layer consisting of a thin discontinuous layer of hard ferromagnetic Co80Pt20 nanoparticles and insulating Al2O3 prepared by alternate sputtering of Co80Pt20 and Al2O3 targets. The maximum TMR obtained was 20.5% at room temperature for FeCo top and bottom electrodes without annealing. Bias voltage dependence of the (NiFe/CoFe)/1.5 nm Al2O3/discontinuous CoPt/2.6 nm Al2O3/(CoFe/NiFe) double tunnel junctions were revealed to be small compared to that of single junctions, the barrier of which was also fabricated by sputtering of an Al2O3 target. © 2000 American Institute of Physics.
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The energy distribution of the ion beam extracted from the compact microwave ion source for extremely low voltage ion extraction was measured with Ar and CO as a discharge gas. The energy distribution was measured by the retarding field method, and changes with respect to the change in gas pressure were observed. The obtained data were arranged by the peak energy and the energy spread. For both gases, the peak energy and the energy spread decreased with an increase in the gas pressure. The energy spread of approximately 5 eV with the peak energy of 15 eV were obtained for Ar gas at the pressure of 10−2 Pa. For CO gas, the peak energy was higher than Ar and approximately 20 eV. The energy spread was 6 eV at the pressure of 10−2 Pa. These values agreed with the peak energy and energy spread that were estimated previously from the mass spectra analysis. Since the ion source was designed to be used in the researches of low energy ion-solid interaction, these characteristics satisfy the requirements for this purpose. © 2002 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2664-2666 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial anatase thin films were fabricated on lattice-matched (−0.2%) LaAlO3 (001) substrates in the layer-by-layer fashion by laser molecular-beam epitaxy. X-ray diffraction and transmission electron microscope show the films to exhibit high crystallinity and atomically defined interfaces. By virtue of the adoption of LaAlO3 substrate, which is transparent to photoexcitation of TiO2, optical band gaps could be determined to be 3.3 eV at room temperature. A photoluminescence band due to recombination of self-trapped excitons was observed at 5 K to give the peak maximum at 2.2 eV. As a result of the high degree of orientation of the epitaxial films, anisotropic optical absorption was clearly observed. © 2001 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3565-3567 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SiGe bulk crystal fabricated by a multicomponent zone-melting method was used as a substrate for epitaxial growth of GaAs. Compared with conventional GaAs/Ge heterostructure, the lattice mismatch of GaAs/Si0.022Ge0.978 was confirmed to be reduced by a decrease of the peak separation of (400) x-ray diffraction from the epitaxial GaAs layer and the substrate. Furthermore, the linewidth of the rocking curve of GaAs on SiGe was found to be narrower than that of GaAs on Ge. These results show that SiGe is promising material as an alternative substrate to Ge for realization of exactly lattice-matched GaAs/SiGe solar cells. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 707-709 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using high-Tc Josephson junctions made of YBa2Cu3O7−δ deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction's dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency. © 1997 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3693-3695 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With a 10 μm×10 μm mesa patterned on Bi2Sr2CaCu2O8 single crystals, we measure the current–voltage (I–V) curves of a stack of intrinsic Josephson junctions. Current steps are observed at an equal voltage spacing of 4 mV when the sample is subjected to microwave radiation at around 7 GHz. With increase of the microwave power, more steps occur while the spacing between neighboring steps does not seem to change. The magnitude of each step depends on the microwave power in an oscillating way. Tuning the microwave frequency causes such steps to occur over separate frequency ranges, and each range is quite narrow. A temperature rise from 4.2 to 14.3 K completely quenches the step structures. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2436-2438 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter describes the relationship between electron mobility and Si-hydrogen bonding configurations in poly-Si thin films after plasma-hydrogenation treatment. A 50-nm-thick amorphous-Si film was crystallized by excimer laser irradiation followed by plasma hydrogenation. Measurements of the Hall effect and Raman scattering demonstrated that mobility increased under the Si-H dominant state and decreased under the Si-H2 dominant state, which were respectively caused by adjusted and excessive hydrogenation times. Mobility degradation was recovered by dissociation of excess H atoms by annealing. The origin of the correlation is discussed in terms of imperfections such as grain boundaries and in-grain defects.© 1998 American Institute of Physics.
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