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  • Articles  (54)
  • 1990-1994  (54)
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  • Articles  (54)
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Year
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2840-2845 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial growth of BaTiO3 and SrTiO3 films by the reactive evaporation method was investigated using reflection high-energy electron diffraction (RHEED). The investigations were carried out using two growth methods: coevaporation and alternate evaporation of the metal elements in an oxygen atmosphere. Atomic layer growth was achieved by the alternate supply of Ba or Sr and Ti on the growing surface. In the case of coevaporation, epitaxial growth occurred in a two-dimensional unit-cell-by-unit-cell mode. The surface of each unit cell is terminated by a (TiO2) layer. Artificial superlattices of BaTiO3/SrTiO3 were fabricated by monitoring the film thickness with the RHEED oscillations.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7833-7838 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of BaTiO3 have been epitaxially grown on Pt(001)/MgO(100) substrates by reactive evaporation. Structural and electrical properties were investigated as a function of film thickness. In situ reflection high-energy electron diffraction and cross-sectional transmission electron microscope observations have revealed that the BaTiO3 films are epitaxially grown on Pt/MgO substrates from the initial stage without any other phase formation. From the images of an atomic force microscope, it has been found that islands of BaTiO3 are present on the bare Pt surface at the initial stage of deposition; the island structure changes to a continuous layer above 1.2 nm in thickness and BaTiO3 grows in a two-dimensional mode. The lattice parameters and the dielectric properties are dependent on the film thickness. Thermodynamic theory was introduced to explain the thickness dependence of the relative dielectric constant εr. Good agreement between the experimental results and the theoretical calculations leads to the conclusion that the thickness dependencies of the lattice parameters and the dielectric constants are caused by the two-dimensional stress due to the lattice mismatch between Pt and BaTiO3 and/or the difference in the thermal expansion coefficients of BaTiO3 and the MgO substrate. © 1994 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3653-3662 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin YBa2Cu3O7−δ epitaxial films were successfully grown in situ on (001) SrTiO3 and MgO substrates by means of ozone-incorporating activated reactive evaporation. The x-ray-diffraction study was carefully examined to determine the structural properties of the grown films. Excellent crystallinity with no interfacial disorders was revealed by the appearance of the Laue oscillations. It was found that in a well lattice-matched YBa2Cu3O7−δ/SrTiO3 system, the crystallinity was deteriorated due to defect introduction at the critical layer thickness hc ( ∼ 130 A(ring)). Interestingly, also in a poorly lattice-matched YBa2Cu3O7−δ/MgO system, excellent crystallinity was revealed even at above hc ( 〈 24 A(ring)). This implies that an anomalous misfit relaxation process exists in the YBa2Cu3O7−δ/MgO system. In such a system, no crystal imperfection of the MgO substrate caused by defect introduction was elucidated by the grazing incidence x-ray scattering, which indicated that the MgO substrate did not contribute to the anomalous misfit relaxation. The anomalous growth manner was also found in YBa2Cu3O7−δ/MgO according to surface morphology investigations. Below 40 A(ring)( (approximately-greater-than) hc), island nucleation growth was found. Above 40 A(ring), it was observed that an atomically smooth surface was obtained and the crystallinity was simultaneously improved. It is suggested that YBa2Cu3O7−δ possesses an anomalous misfit relaxation mechanism, and that especially in the growth on MgO, it couples with the characteristic growth behavior at the initial stage.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1735-1740 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several (111) oriented 56Fe3O4 films containing a 5-A(ring)-thick 57Fe3O4 probe layer at or below the surface were grown epitaxially on the α-Al2O3 (0001) surface by a reactive vapor deposition method. Conversion electron Mössbauer spectroscopy was applied at 6, 78, and 300 K by using a recently developed helium-filled proportional counter. The well-crystallized surface has been found to be surprisingly stable even in air as characterized by the Mössbauer parameters that are almost the same as for the bulk. Moreover, the Verwey transition was detected clearly even in the 5-A(ring)-thick surface layer. However, the ferrous components seem to have changed their Mössbauer parameters probably because of their sensitivity to any crystalline field modifications in the surface. Generally speaking, the quality of epitaxial Fe3O4 films is very high: Any unusual surface state, if present, is confined in a shallow depth of ≤ 5 A(ring).
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 677-679 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting Nd-Ce-Cu-O thin films were epitaxially grown on SrTiO3 (100) by activated reactive evaporation. As-grown films showed the metallic temperature dependence of the resistivity and superconducting transition at 12.5 K (R=0). The remarkable parallel shift of the onset temperature of the resistive transition in the magnetic fields was observed. Ginzburg–Landau coherence lengths along the c axis and in the basal plane are 7 and 96 A(ring), respectively.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 527-529 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferroelectric BaTiO3 thin films were directly and epitaxially grown on SrTiO3 single crystal and epitaxial Pt film substrates by activated reactive evaporation. The substrate temperature was around 600 °C. For (100) oriented as-grown films, a typical ferroelectric hysteresis loop and a maximum of dielectric constant at about 115 °C were observed. The resistivity was as high as 109 Ω cm and the breakdown voltage was 2.7 MV/cm for as-grown BaTiO3 films.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 683-685 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have, for the first time, made quasi-particle tunneling measurements on a YBa2Cu3O7−x(001)/Y2O3 (001)/YBa2 Cu3 O7−x (001)junction, which was epitaxially grown on a MgO(100) substrate in an in-situ process. Both layers of YBa2 Cu3 O7−x showed the same superconducting transition of Tc end =86 K with ΔT(R=10–90%)=1.5 K. Quasi-particle tunneling in the direction perpendicular to the Cu-O planes was measured. A gap parameter Δ(4.5 K) of 9.0±0.2 meV and a value of 2Δ/kTc of 3.5+0.4−0.6 were obtained.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 9 (1990), S. 1376-1378 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 775-776 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Samples were prepared starting from metallic compositions of Cal_xSrx:Cu=l-iy:l with 0.4^x^0.7 and O^^^O.l. Typically, a gold capsule was filled with an intimate mixture of Ca0 3Sr0 7CuO2 (low-pressure phase) and fine powder of CuO, pressed almost isostatically up to 6 GPa using a classical ...
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 28 (1993), S. 4223-4228 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A study was carried out of the induction plasma melting of alumina powders (particle mean diameter, ¯d p=24.5 μm), (Ar/H2 or Ar/N2 plasma, plate power, 40 kW) under reduced pressure conditions (400 torr). The results reveal that in the process, partial vaporization of the alumina powders takes place in the hot region of the discharge. As the molten particles cool down and solidify, the deposits from the vapour phase was formed with the spheroidized particles. In all treatments with the Ar/H2 and Ar/N2 plasmas, a condensate of ultrafine alumina fume (d p〈200 nm) was obtained. The fine particles consisted essentially of metastable γ-, δ- and θ-phases. Needle-like crystals(0.1–0.3 μm diameter, by 5–15 μm long) were observed when operating with an Ar/N2 plasma at powder feed rates exceeding 10 g min−1. Electron diffraction analysis revealed that the needles were whiskers, whose structure was very similar to κ- or χ-aluminas with an hexagonal close-packed oxygen lattice. The change of morphology is related to the degree of supersaturation in the vapour phase.
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